“We have made great progress in the field of plasma acceleration,” says Andreas Maier, DESY’s lead scientist for plasma acceleration, “but this is an endeavour that has only just started, and we still have a bit of homework to do to get the system integrated with the injector complexes of a synchrotron, which is our final goal.”

Riding a wave

PWA has the potential to radically miniaturise particle accelerators. Plasma waves are generated when a laser pulse or particle beam ploughs through a millimetres-long hydrogen-filled capillary, displacing electrons and creating a wake of alternating positive and negative charge regions behind it. The process is akin to flotsam and jetsam being accelerated in the wake of a speedboat, and the plasma “wakefields” can be thousands of times stronger than the electric fields in conventional accelerators, allowing particles to gain hundreds of MeV in just a few millimetres. But beam quality and intensity are significant challenges in such narrow confines.

In a first study, a team from the LUX experiment at DESY and the University of Hamburg demonstrated, for the first time, a two-stage correction system to dramatically reduce the energy spread of accelerated electron beams. The first stage stretches the longitudinal extent of the beam from a few femtoseconds to several picoseconds using a series of four zigzagging bending magnets called a magnetic chicane. Next, a radio-frequency cavity reduces the energy variation to below 0.1%, bringing the beam quality in line with conventional accelerators.

“We basically trade beam current for energy stability,” explains Paul Winkler, lead author of a recent publication on active energy compression. “But for the intended application of a synchrotron injector, we would need to stretch the electron bunches anyway. As a result, we achieved performance levels so far only associated with conventional accelerators.”

But producing high-quality beams is only half the battle. To make laser-driven PWA a practical proposition, bunches must be accelerated not just once a second, like at LUX, but hundreds or thousands of times per second. This has now been demonstrated by KALDERA, DESY’s new high-power laser system (see “Beam quality and bunch rate” image).

“Already, on the first try, we were able to accelerate 100 electron bunches per second,” says principal investigator Manuel Kirchen, who emphasises the complementarity of the two advances. The team now plans to scale up the energy and deploy “active stabilisation” to improve beam quality. “The next major goal is to demonstrate that we can contin­uously run the plasma accelerators with high stability,” he says.

With the exception of CERN’s AWAKE experiment (CERN Courier May/June 2024 p25), almost all plasma-wakefield accelerators are designed with medical or industrial applications in mind. Medical applications are particularly promising as they require lower beam energies and place less demanding constraints on beam quality. Advances such as those reported by LUX and KALDERA raise confidence in this new technology and could eventually open the door to cheaper and more portable X-ray equipment, allowing medical imaging and cancer therapy to take place in university labs and hospitals.

The post Double plasma progress at DESY appeared first on CERN Courier.

CERN Director-General Fabiola Gianotti estimated the integral FCC programme to offer unparalleled opportunities to explore physics at the shortest distances, and noted growing support and enthusiasm for the programme within the community. That enthusiasm is reflected in the growing collaboration: the FCC collaboration now includes 162 institutes from 38 countries, with 28 new Memoranda of Understanding signed in the past year. These include new partnerships in Latin America, Asia and Ukraine, as well as Statements of Intent from the US and Canada. The FCC vision has also gained visibility in high-level policy dialogues, including the Draghi report on European competitiveness. Scientific plenaries and parallel sessions highlighted updates on simulation tools, rare-process searches and strategies to probe beyond the Standard Model. Detector R&D has progressed significantly, with prototyping, software development and AI-driven simulations advancing rapidly.

In accelerator design, developments included updated lattice and optics concepts involving global “head-on” compensation (using opposing beam interactions) and local chromaticity corrections (to the dependence of beam optics on particle energy). Refinements were also presented to injection schemes, beam collimation and the mitigation of collective effects. A central tool in these efforts is the Xsuite simulation platform, whose capabilities now include spin tracking and modelling based on real collider environments such as SuperKEKB.

Technical innovations also came to the fore. The superconducting RF system for FCC-ee includes 400 MHz Nb/Cu cavities for low-energy operation and 800 MHz Nb cavities for higher-energy modes. The introduction of reverse-phase operation and new RF source concepts – such as the tristron, with energy efficiencies above 90% (CERN Courier May/June 2025 p30) – represent major design advances.

Design developments

Vacuum technologies based on ultrathin NEG coating and discrete photon stops, as well as industrialisation strategies for cost control, are under active development. For FCC-hh, high-field magnet R&D continues on both Nb₃Sn prototypes and high-temperature superconductors.

Sessions on technical infrastructure explored everything from grid design, cryogenics and RF power to heat recovery, robotics and safety systems. Sustainability concepts, including renewable energy integration and hydrogen storage, showcased the project’s interdisciplinary scope and long-term environmental planning.

FCC Week 2025 extended well beyond the conference venue, turning Vienna into a vibrant hub for public science outreach

The Early Career Researchers forum drew nearly 100 participants for discussions on sustainability, governance and societal impact. The session culminated in a commitment to inclusive collaboration, echoed by the quote from Austrian-born artist, architect and environmentalist Friedensreich Hundertwasser (1928–2000): “Those who do not honour the past lose the future. Those who destroy their roots cannot grow.”

This spirit of openness and public connection also defined the week’s city-wide engagement. FCC Week 2025 extended well beyond the conference venue, turning Vienna into a vibrant hub for public science outreach. In particular, the “Big Science, Big Impact” session – co-organised with the Austrian Federal Economic Chamber (WKO) – highlighted CERN’s broader role in economic development. Daniel Pawel Zawarczynski (WKO) shared examples of small and medium enterprise growth and technology transfer, noting that CERN participation can open new markets, from tunnelling to aerospace. Economist Gabriel Felbermayr referred to a recent WIFO analysis indicating a benefit-to-cost ratio for the FCC greater than 1.2 under conservative assumptions. The FCC is not only a tool for discovery, observed Johannes Gutleber (CERN), but also a platform enabling technology development, open software innovation and workforce training.

The FCC awards celebrate the creativity, rigour and passion that early-career researchers bring to the programme. This year, Tsz Hong Kwok (University of Zürich) and Audrey Piccini (CERN) won poster prizes, Sara Aumiller (TU München) and Elaf Musa (DESY) received innovation awards, and Ivan Karpov (CERN) and Nicolas Vallis (PSI) were honoured with paper prizes sponsored by Physical Review Accelerators and Beams. As CERN Council President Costas Fountas reminded participants, the FCC is not only about pushing the frontiers of knowledge, but also about enabling a new generation of ideas, collaborations and societal progress.

The post A new phase for the FCC appeared first on CERN Courier.

Particle accelerators can be surprisingly temperamental machines. Expertise, specialisation and experience is needed to maintain their performance. Nonlinear and resonant effects keep accelerator engineers and physicists up late into the night. With so many variables to juggle and fine-tune, even the most seasoned experts will be stretched by future colliders. Can artificial intelligence (AI) help?

Proposed solutions take inspiration from space telescopes. The two fields have been jockeying to innovate since the Hubble Space Telescope launched with minimal automation in 1990. In the 2000s, multiple space missions tested AI for fault detection and onboard decision-making, before the LHC took a notable step forward for colliders in the 2010s by incorporating machine learning (ML) in trigger decisions. Most recently, the James Webb Space Telescope launched in 2021 using AI-driven autonomous control systems for mirror alignment, thermal balancing and scheduling science operations with minimal intervention from the ground. The new Efficient Particle Accelerators project at CERN, which I have led since its approval in 2023, is now rolling out AI at scale across CERN’s accelerator complex (see “Dynamic and adaptive” image.

AI-driven automation will only become more necessary in the future. As well as being unprecedented in size and complexity, future accelerators will also have to navigate new constraints such as fluctuating energy availability from intermittent sources like wind and solar power, requiring highly adaptive and dynamic machine operation. This would represent a step change in complexity and scale. A new equipment integration paradigm would automate accelerator operation, equipment maintenance, fault analysis and recovery. Every item of equipment will need to be fully digitalised and able to auto-configure, auto-stabilise, auto-analyse and auto-recover. Like a driverless car, instrumentation and software layers must also be added for safe and efficient performance.

On-site human intervention of the LHC could be treated as a last resort – or perhaps designed out entirely

The final consideration is full virtualisation. While space telescopes are famously inaccessible once deployed, a machine like the Future Circular Collider (FCC) would present similar challenges. Given the scale and number of components, on-site human intervention should be treated as a last resort – or perhaps designed out entirely. This requires a new approach: equipment must be engineered for autonomy from the outset – with built-in margins, high reliability, modular designs and redundancy. Emerging technologies like robotic inspection, automated recovery systems and digital twins will play a central role in enabling this. A digital twin – a real-time, data-driven virtual replica of the accelerator – can be used to train and constrain control algorithms, test scenarios safely and support predictive diagnostics. Combined with differentiable simulations and layered instrumentation, these tools will make autonomous operation not just feasible, but optimal.

The field is moving fast. Recent advances allow us to rethink how humans interact with complex machines – not by tweaking hardware parameters, but by expressing intent at a higher level. Generative pre-trained transformers, a class of large language models, open the door to prompting machines with concepts rather than step-by-step instructions. While further R&D is needed for robust AI copilots, tailor-made ML models have already become standard tools for parameter optimisation, virtual diagnostics and anomaly detection across CERN’s accelerator landscape.

Progress is diverse. AI can reconstruct LHC bunch profiles using signals from wall current monitors, analyse camera images to spot anomalies in the “dump kickers” that safely remove beams, or even identify malfunctioning beam-position monitors. In the following, I identify four different types of AI that have been successfully deployed across CERN’s accelerator complex. They are merely the harbingers of a whole new way of operating CERN’s accelerators.

1. Beam steering with reinforcement learning

In 2020, LINAC4 became the new first link in the LHC’s modernised proton accelerator chain – and quickly became an early success story for AI-assisted control in particle accelerators.

Small deviations in a particle beam’s path within the vacuum chamber can have a significant impact, including beam loss, equipment damage or degraded beam quality. Beams must stay precisely centred in the beampipe to maintain stability and efficiency. But their trajectory is sensitive to small variations in magnet strength, temperature, radiofrequency phase and even ground vibrations. Worse still, errors typically accumulate along the accelerator, compounding the problem. Beam-position monitors (BPMs) provide measurements at discrete points – often noisy – while steering corrections are applied via small dipole corrector magnets, typically using model-based correction algorithms.

In 2019, the reinforcement learning (RL) algorithm normalised advantage function (NAF) was trained online to steer the H^– beam in the horizontal plane of LINAC4 during commissioning. In RL, an agent learns by interacting with its environment and receiving rewards that guide it toward better decisions. NAF uses a neural network to model the so-called Q-function that estimates rewards in RL and uses this to continuously refine its control policy.

Initially, the algorithm required many attempts to find an effective strategy, and in early iterations it occasionally worsened the beam trajectory, but as training progressed, performance improved rapidly. Eventually, the agent achieved a final trajectory better aligned than the goal of an RMS of 1 mm (see “Beam steering” figure).

This experiment demonstrated that RL can learn effective control policies for accelerator-physics problems within a reasonable amount of time. The agent was fully trained after about 300 iterations, or 30 minutes of beam time, making online training feasible. Since 2019, the use of AI techniques has expanded significantly across accelerator labs worldwide, targeting more and more problems that don’t have any classical solution. At CERN, tools such as GeOFF (Generic Optimisation Framework and Front­end) have been developed to standardise and scale these approaches throughout the accelerator complex.

2. Efficient injection with Bayesian optimisation

Bayesian optimisation (BO) is a global optimisation technique that uses a probabilistic model to find the optimal parameters of a system by balancing exploration and exploitation, making it ideal for expensive or noisy evaluations. A game-changing example of its use is the record-breaking LHC ion run in 2024. BO was extensively used all along the ion chain, and made a significant difference in LEIR (the low-energy ion ring, the first synchrotron in the chain) and in the Super Proton Synchrotron (SPS, the last accelerator before the LHC). In LEIR, most processes are no longer manually optimised, but the multi-turn injection process is still non-trivial and depends on various longitudinal and transverse parameters from its injector LINAC3.

In heavy-ion accelerators, particles are injected in a partially stripped charge state and must be converted to higher charge states at different stages for efficient acceleration. In the LHC ion injector chain, the stripping foil between LINAC3 and LEIR raises the charge of the lead ions from Pb²⁷⁺ to Pb⁵⁴⁺. A second stripping foil, between the PS and SPS, fully ionises the beam to Pb⁸²⁺ ions for final acceleration toward the LHC. These foils degrade over time due to thermal stress, radiation damage and sputtering, and must be remotely exchanged using a rotating wheel mechanism. Because each new foil has slightly different stripping efficiency and scattering properties, beam transmission must be re-optimised – a task that traditionally required expert manual tuning.

In 2024 it was successfully demonstrated that BO with embedded physics constraints can efficiently optimise the 21 most important parameters between LEIR and the LINAC3 injector. Following a stripping foil exchange, the algorithm restored the accumulated beam intensity in LEIR to better than nominal levels within just a few dozen iterations (see “Quick recovery” figure).

This example shows how AI can now match or outperform expert human tuning, significantly reducing recovery time, freeing up operator bandwidth and improving overall machine availability.

3. Adaptively correcting the 50 Hz ripple

In high-precision accelerator systems, even tiny perturbations can have significant effects. One such disturbance is the 50 Hz ripple in power supplies – small periodic fluctuations in current that originate from the electrical grid. While these ripples were historically only a concern for slow-extracted proton beams sent to fixed-target experiments, 2024 revealed a broader impact.

In the SPS, adaptive Bayesian optimisation (ABO) was deployed to control this ripple in real time. ABO extends BO by learning the objective not only as a function of the control parameters, but also as a function of time, which then allows continuous control through forecasting.

The algorithm generated shot-by-shot feed-forward corrections to inject precise counter-noise into the voltage regulation of one of the quadrupole magnet circuits. This approach was already in use for the North Area proton beams, but in summer 2024 it was discovered that even for high-intensity proton beams bound for the LHC, the same ripple could contribute to beam losses at low energy.

Thanks to existing ML frameworks, prior experience with ripple compensation and available hardware for active noise injection, the fix could be implemented quickly. While the gains for protons were modest – around 1% improvement in losses – the impact for LHC ion beams was far more dramatic. Correcting the 50 Hz ripple increased ion transmission by more than 15%. ABO is therefore now active whenever ions are accelerated, improving transmission and supporting the record beam intensity achieved in 2024 (see “SPS intensity” figure).

4. Predicting hysteresis with transformers

Another outstanding issue in today’s multi-cycling synchrotrons with iron-dominated electromagnets is correcting for magnetic hysteresis – a phenomenon where the magnetic field depends not only on the current but also on its cycling history. Cumbersome mitigation strategies include playing dummy cycles and manually re-tuning parameters after each change in magnetic history.

While phenomenological hysteresis models exist, their accuracy is typically insufficient for precise beam control. ML offers a path forward, especially when supported by high-quality field measurement data. Recent work using temporal fusion transformers – a deep-learning architecture designed for multivariate time-series prediction – has demonstrated that ML-based models can accurately predict field deviations from the programmed transfer function across different SPS magnetic cycles (see “SPS hysteresis” figure). This hysteresis model is now used in the SPS control room to provide feed-forward corrections – pre-emptive adjustments to magnet currents based on the predicted magnetic state – ensuring field stability without waiting for feedback from beam measurements and manual adjustments.

A blueprint for the future

With the Efficient Particle Accelerators project, CERN is developing a blueprint for the next generation of autonomous equipment. This includes concepts for continuous self-analysis, anomaly detection and new layers of “Internet of Things” instrumentation that support auto-configuration and predictive maintenance. The focus is on making it easier to integrate smart software layers. Full results are expected by the end of LHC Run 3, with robust frameworks ready for deployment in Run 4.

AI can now match or outperform expert human tuning, significantly reducing recovery time and improving overall machine availability

The goal is ambitious: to reduce maintenance effort by at least 50% wherever these frameworks are applied. This is based on a realistic assumption – already today, about half of all interventions across the CERN accelerator complex are performed remotely, a number that continues to grow. With current technologies, many of these could be fully automated.

Together, these developments will not only improve the operability and resilience of today’s accelerators, but also lay the foundation for CERN’s future machines, where human intervention during operation may become the exception rather than the rule. AI is set to transform how we design, build and operate accelerators – and how we do science itself. It opens the door to new models of R&D, innovation and deep collaboration with industry. 

The post Accelerators on autopilot appeared first on CERN Courier.

The klystron was invented in 1937 by two American brothers, Russell and Sigurd Varian. The Varians wanted to improve aircraft radar systems. At the time, there was a growing need for better high-frequency amplification to detect objects at a distance using radar, a critical technology in the lead-up to World War II.

The Varian’s RF source operated around 3.2 GHz, or a wavelength of about 9.4 cm, in the microwave region of the electromagnetic spectrum. At the time, this was an extraordinarily high frequency – conventional vacuum tubes struggled beyond 300 MHz. Microwave wavelengths promised better resolution, less noise, and the ability to penetrate rain and fog. Crucially, antennas could be small enough to fit on ships and planes. But the source was far too weak for radar.

Klystrons are ubiquitous in medical, industrial and research accelerators – and not least in the next generation of Higgs factories

The Varians’ genius was to invent a way to amplify the electromagnetic signal by up to 30 dB, or a factor of 1000. The US and British military used the klystron for airborne radar, submarine detection of U-boats in the Atlantic and naval gun targeting beyond visual range. Radar helped win the Battle of Britain, the Battle of the Atlantic and Pacific naval battles, making surprise attacks harder by giving advance warning. Winston Churchill called radar “the secret weapon of WWII”, and the klystron was one of its enabling technologies.

With its high gain and narrow bandwidth, the klystron was the first practical microwave amplifier and became foundational in radio-frequency (RF) technology. This was the first time anyone had efficiently amplified microwaves with stability and directionality. Klystrons have since been used in satellite communication, broadcasting and particle accelerators, where they power the resonant RF cavities that accelerate the beams. Klystrons are therefore ubiquitous in medical, industrial and research accelerators – and not least in the next generation of Higgs factories, which are central to the future of high-energy physics.

Klystrons and the Higgs

Hadron colliders like the LHC tend to be circular. Their fundamental energy limit is given by the maximum strength of the bending magnets and the circumference of the tunnel. A handful of RF cavities repeatedly accelerate beams of protons or ions after hundreds or thousands of bending magnets force the beams to loop back through them.

Thanks to their clean and precisely controllable collisions, all Higgs factories under consideration are electron–positron colliders. Electron–positron colliders can be either circular or linear in construction. The dynamics of circular electron–positron colliders are radically different as the particles are 2000 times lighter than protons. The strength required from the bending magnets is relatively low for any practical circumference, however, the energy of the particles must be continually replenished, as they radiate away energy in the bends through synchrotron radiation, requiring hundreds of RF cavities. RF cavities are equally important in the linear case. Here, all the energy must be imparted in a single pass, with each cavity accelerating the beam only once, requiring either hundreds or even thousands of RF cavities.

Either way, 50 to 60% of the total energy consumed by an electron-positron collider is used for RF acceleration, compared to a relatively small fraction in a hadron collider. Efficiently powering the RF cavities is of paramount importance to the energy efficiency and cost effectiveness of the facility as a whole. RF acceleration is therefore of far greater significance at electron–positron colliders than at hadron colliders.

From a pen to a mid-size car

RF cavities cannot simply be plugged into the wall. These finely tuned resonant structures must be excited by RF power – an alternating microwave electromagnetic field that is supplied through waveguides at the appropriate frequency. Due to the geometry of resonant cavities, this excites an on-axis oscillating electrical field. Particles that arrive when the electrical field has the right direction are accelerated. For this reason, particles in an accelerator travel in bunches separated by a long distance, during which the RF field is not optimised for acceleration.

Despite the development of modern solid-state amplifiers, the Varians’ klystron is still the most practical technology to generate RF when the power required is in the MW level. They can be as small as a pen or as large and heavy as a mid-size car, depending on the frequency and power required. Linear colliders use higher frequency because they also come with higher gradients and make the linac shorter, whereas a circular collider does not need high gradients as the energy to be given each turn is smaller.

Klystrons fall under the general classification of vacuum tubes – fully enclosed miniature electron accelerators with their own source, accelerating path and “interaction region” where the RF field is produced. Their name is derived from the Greek verb describing the action of waves crashing against the seashore. In a klystron, RF power is generated when electrons crash against a decelerating electric field.

Every klystron contains at least two cavities: an input and an output. The input cavity is powered by a weak RF source that must be amplified. The output cavity generates the strongly amplified RF signal generated by the klystron. All this comes encapsulated in an ultra-high vacuum volume inside the field of a solenoid for focusing (see “Operating principle” figure).

Thanks to the efforts made in recent years, high-efficiency klystrons are now approaching the ultimate theoretical limit

Inside the klystron, electrons leave a heated cathode and are accelerated by a high voltage applied between the cathode and the anode. As they are being pushed forward, a small input RF signal is applied to the input cavity, either accelerating or decelerating the electrons according to their time of arrival. After a long drift, late-emitted accelerated electrons catch up with early-emitted decelerated electrons, intersecting with those that did not see any net accelerating force. This is called velocity bunching.

A second, passive accelerating cavity is placed at the location where maximum bunching occurs. Though of a comparable design, this cavity behaves in an inverse fashion to those used in particle accelerators. Rather than converting the energy of an electromagnetic field into the kinetic energy of particles, the kinetic energy of particles is converted into RF electromagnetic waves. This process can be enhanced by the presence of other passive cavities in between the already mentioned two, as well as by several iterations of bunching and de-bunching before reaching the output cavity. Once decelerated, the spent beam finishes its life in a dump or a water-cooled collector.

Optimising efficiency

Klystrons are ultimately RF amplifiers with a very high gain of the order of 30 to 60 dB and a very narrow bandwidth. They can be built at any frequency from a few hundred MHz to tens of GHz, but each operates within a very small range of frequencies called the bandwidth. After broadcasting became reliant on wider bandwidth vacuum tubes, their application in particle accelerators turned into a small market for high-power klystrons. Most klystrons for science are manufactured by a handful of companies which offer a limited number of models that have been in operation for decades. Their frequency, power and duty cycle may not correspond to the specifications of a new accelerator being considered – and in most cases, little or no thought has been given to energy efficiency or carbon footprint.

When searching for suitable solutions for the next particle-physics collider, however, optimising the energy efficiency of klystrons and other devices that will determine the final energy bill and CO₂ emissions is a task of the utmost importance. Therefore, nearly a decade ago, RF experts at CERN and the University of Lancaster began the High-Efficiency Klystron (HEK) project to maximise beam-to-RF efficiency: the fraction of the power contained in the klystron’s electron beam that is converted into RF power by the output cavity.

The complexity of klystrons resides on the very nonlinear fields to which the electrons are subjected. In the cathode and the first stages of electrostatic acceleration, the collective effect of “space-charge” forces between the electrons determines the strongly nonlinear dynamics of the beam. The same is true when the bunching tightens along the tube, with mutual repulsion between the electrons preventing optimal bunching at the output cavity.

For this reason, designing klystrons is not susceptible to simple analytical calculations. Since 2017, CERN has developed a code called KlyC that simulates the beam along the klystron channel and optimises parameters such as frequency and distance between cavities 100 to 1000 times faster than commercial 3D codes. KlyC is available in the public domain and is being used by an ever-growing list of labs and industrial partners.

Perveance

The main characteristic of a klystron is an obscure magnitude inherited from electron-gun design called perveance. For small perveances, space-charge forces are small, due to either high energy or low intensity, making bunching easy. For large perveances, space-charge forces oppose bunching, lowering beam-to-RF efficiency. High-power klystrons require large currents and therefore high perveances. One way to produce highly efficient, high-power klystrons is therefore for multiple cathodes to generate multiple low-perveance electron beams in a “multi-beam” (MB) klystron.

Overall, there is an almost linear dependence between perveance and efficiency. Thanks to the efforts made in recent years, high-efficiency klystrons are now outperforming industrial klystrons by 10% in efficiency for all values of perveance, and approaching the ultimate theoretical limit (see “Battling space charge” figure).

One of the first designs to be brought to life was based on the E37113, a pulsed klystron with 6 MW peak power working in the X-band at 12 GHz, commercialised by CANON ETD. This klystron is currently used in the test facility at CERN for validating CLIC RF prototypes, which could greatly benefit from a larger power. As part of a collaboration with CERN, CANON ETD built a new tube, according to the design optimised at CERN, to reach a beam-to-RF efficiency of 57% instead of the original 42% (see “CLIC klystron” image and CERN Courier September/October 2022 p9).

As its interfaces with the high-voltage (HV) source and solenoid were kept identical, one can now benefit from 8 MW of RF power for the same energy consumption as before. As changes in the manufacturing of the tube channel are just a small fraction of the manufacture of the instrument, its price should not increase considerably, even if more accurate production methods are required.

In pursuit of power

Another successful example of re-designing a tube for high efficiency is the TH2167 – the klystron behind the LHC, which is manufactured by Thales. Originally exhibiting a beam-to-RF efficiency of 60%, it was re-designed by the CERN team to gain 10% and reach 70% efficiency, while again using the same HV source and solenoid. The tube prototype has been built and is currently at CERN, where it has demonstrated the capacity to generate 350 kW of RF power with the same input energy as previously required to produce 300 kW. This power will be decisive when dealing with the higher intensity beam expected after the LHC luminosity upgrade. And all this again for a price comparable to previous models (see “High-luminosity gains” image).

The quest for the highest efficiency is not over yet. The CERN team is currently working on a design that could power the proposed Future Circular collider (FCC). Using about a hundred accelerating cavities, the electron and positron beams will need to be replenished with 100 MW of RF power, and energy efficiency is imperative.

The quest for the highest efficiency is not over yet

Although the same tube in use for the LHC, now boosted to 70% efficiency, could be used to power the FCC, CERN is working towards a vacuum tube that could reach an efficiency over 80%. A two-stage multi-beam klystron was initially designed that was capable of reaching 86% efficiency and generating 1 MW of continuous-wave power (see “Towards an FCC klystron” figure).

Motivated by recent changes in FCC parameters, we have rediscovered an old device called a tristron, which is not a conventional klystron but a “gridded tube” where the electron beam bunching mechanism is different. Tristons have a lower power gain but much greater flexibility. Simulations have confirmed that they can reach efficiencies as high as 90%. This could be a disruptive technology with applications well beyond accelerators. Manufacturing a prototype is an excellent opportunity for knowledge transfer from fundamental research to industrial applications.

The post Powering into the future appeared first on CERN Courier.

The deadline for submitting inputs to the 2026 update of the European Strategy for Particle Physics (ESPP) passed on 31 March. A total of 263 submissions, ranging from individual to national perspectives, express the priorities of the high-energy physics community (see “Community inputs” figure). These inputs will be distilled by expert panels in preparation for an Open Symposium that will be held in Venice from 23 to 27 June (CERN Courier March/April 2025 p11).

Launched by the CERN Council in March 2024, the stated aim of the 2026 update to the ESPP is to develop a visionary and concrete plan that greatly advances human knowledge in fundamental physics, in particular through the realisation of the next flagship project at CERN. The community-wide process, which is due to submit recom­mendations to Council by the end of the year, is also expected to prioritise alternative options to be pursued if the preferred project turns out not to be feasible or competitive.

“We are heartened to see so many rich and varied contributions, in particular the national input and the various proposals for the next large-scale accelerator project at CERN,” says strategy secretary Karl Jakobs of the University of Freiburg, speaking on behalf of the European Strategy Group (ESG). “We thank everyone for their hard work and rigour.”

Two proposals for flagship colliders are at an advanced stage: a Future Circular Collider (FCC) and a Linear Collider Facility (LCF). As recommended in the 2020 strategy update, a feasibility study for the FCC was released on 31 March, describing a 91 km-circumference infrastructure that could host an electron–positron Higgs and electroweak factory followed by an energy-frontier hadron collider at a later stage. Inputs for an electron–positron LCF cover potential starting configurations based on Compact Linear Collider (CLIC) or International Linear Collider (ILC) technologies. It is proposed that the latter LCF could be upgraded using CLIC, Cool Copper Collider, plasma-wakefield or energy-recovery technologies and designs. Other proposals outline a muon collider and a possible plasma-wakefield collider, as well as potential “bridging” projects to a future flagship collider. Among the latter are LEP3 and LHeC, which would site an electron–positron and an electron–proton collider, respectively, in the existing LHC tunnel. For the LHeC, an additional energy-recovery linac would need to be added to CERN’s accelerator complex.

Future choices

In probing beyond the Standard Model and more deeply studying the Higgs boson and its electroweak domain, next-generation colliders will pick up where the High-Luminosity LHC (HL-LHC) leaves off. In a joint submission, the ATLAS and CMS collaborations presented physics projections which suggest that the HL-LHC will be able to: observe the H → µ⁺µ^– and H → Zγ decays of the Higgs boson; observe Standard Model di-Higgs production; and measure the Higgs’ trilinear self-coupling with a precision better than 30%. The joint document also highlights the need for further progress in high-precision theoretical calculations aligned with the demands of the HL-LHC and serves as important input to the discussion on the choice of a future collider at CERN.

Neutrinos and cosmic messengers, dark matter and the dark sector, strong interactions and flavour physics also attracted many inputs, allowing priorities in non-collider physics to complement collider programmes. Underpinning the community’s physics aspirations are numerous submissions in the categories of accelerator science and technology, detector instrumentation and computing. Progress in these technologies is vital for the realisation of a post-LHC collider, which was also reflected by the recommendation of the 2020 strategy update to define R&D roadmaps. The scientific and technical inputs will be reviewed by the Physics Preparatory Group (PPG), which will conduct comparative assessments of the scientific potential of various proposed projects against defined physics benchmarks.

We are heartened to see so many rich and varied contributions

Key to the ESPP 2026 update are 57 national and national-laboratory submissions, including some from outside Europe. Most identify the FCC as the preferred project to succeed the LHC. If the FCC is found to be unfeasible, many national communities propose that a linear collider at CERN should be pursued, while taking into account the global context: a 250 GeV linear collider may not be competitive if China decides to proceed with a Circular Electron Positron Collider at a comparable energy on the anticipated timescale, potentially motivating a higher energy electron–positron machine or a proton–proton collider instead.

Complex process

In its review, the ESG will take the physics reach of proposed colliders as well as other factors into account. This complex process will be undertaken by seven working groups, addressing: national inputs; diversity in European particle physics; project comparison; implementation of the strategy and deliverability of large projects; relations with other fields of physics; sustainability and environmental impact; public engagement, education, communication and social and career aspects for the next generation; and knowledge and technology transfer. “The ESG and the PPG have their work cut out and we look forward to further strong participation by the full community, in particular at the Open Symposium,” says Jakobs.

A briefing book prepared by the PPG based on the community input and discussions at the Open Symposium will be submitted to the ESG by the end of September for consideration during a five-day-long drafting session, which is scheduled to take place from 1 to 5 December. The CERN Council will then review the final ESG recommendations ahead of a special session to be held in Budapest in May 2026.

The post European strategy update: the community speaks appeared first on CERN Courier.

The FCC is a proposed collider infrastructure that could succeed the LHC in the 2040s. Its scientific motivation stems from the discovery in 2012 of the final particle of the Standard Model (SM), the Higgs boson, with a mass of just 125 GeV, and the wealth of precision measurements and exploratory searches during 15 years of LHC operations that have excluded many signatures of new physics at the TeV scale. The report argues that the FCC is particularly well equipped to study the Higgs and associated electroweak sectors in detail and that it provides a broad and powerful exploratory tool that would push the limits of the unknown as far as possible.

The report describes how the FCC will seek to address key domains formulated in the 2013 and 2020 ESPP updates, including: mapping the properties of the Higgs and electroweak gauge bosons with accuracies orders of magnitude better than today to probe the processes that led to the emergence of the Brout–Englert–Higgs field’s nonzero vacuum expectation value; ensuring a comprehensive and accurate campaign of precision electroweak, quantum chromodynamics, flavour and top-quark measurements sensitive to tiny deviations from the SM, probing energy scales far beyond the direct kinematic reach; improving by orders of magnitude the sensitivity to rare and elusive phenomena at low energies, including the possible discovery of light particles with very small couplings such as those relevant to the search for dark matter; and increasing by at least an order of magnitude the direct discovery reach for new particles at the energy frontier.

This technology has significant potential for industrial and societal applications

The FCC research programme outlines two possible stages: an electron–positron collider (FCC-ee) running at several centre-of-mass energies to serve as a Higgs, electroweak and top-quark factory, followed at a later stage by a proton–proton collider (FCC-hh) operating at an unprecedented collision energy. An FCC-ee with four detectors is judged to be “the electroweak, Higgs and top factory project with the highest luminosity proposed to date”, able to produce 6 × 10¹² Z bosons, 2.4 × 10⁸ W pairs, almost 3 × 10⁶ Higgs bosons, and 2 × 10⁶ top-quark pairs over 15 years of operations. Its versatile RF system would enable flexibility in the running sequence, states the report, allowing experimenters to move between physics programmes and scan through energies at ease. The report also outlines how the FCC-ee injector offers opportunities for other branches of science, including the production of spatially coherent photon beams with a brightness several orders of magnitude higher than any existing or planned light source.

The estimated cost of the construction of the FCC-ee is CHF 15.3 billion. This investment, which would be distributed over a period of about 15 years starting from the early 2030s, includes civil engineering, technical infrastructure, electron and positron accelerators, and four detectors.

Ready for construction

The report describes how key FCC-ee design approaches, such as a double-ring layout, top-up injection with a full-energy booster, a crab-waist collision scheme, and precise energy calibration, have been demonstrated at several previous or presently operating colliders. The FCC-ee is thus “technically ready for construction” and is projected to deliver four-to-five orders of magnitude higher luminosity per unit electrical power than LEP. During operation, its energy consumption is estimated to vary
from 1.1 to 1.8 TWh/y depending on the operation mode compared to CERN’s current consumption of about 1.3 TWh/y. Decarbonised energy including an ever-growing contribution from renewable sources would be the main source of energy for the FCC. Ongoing technology R&D aims at further increasing FCC-ee’s energy efficiency (see “Powering into the future”).

Assuming 14 T Nb₃Sn magnet technology as a baseline design, a subsequent hadron collider with a centre-of-mass energy of 85 TeV entering operation in the early 2070s would extend the energy frontier by a factor six and provide an integrated luminosity five to 10 times higher than that of the HL-LHC during 25 years of operation. With four detectors, FCC-hh would increase the mass reach of direct searches for new particles to several tens of TeV, probing a broad spectrum of beyond-the-SM theories and potentially identifying the sources of any deviations found in precision measurements at FCC-ee, especially those involving the Higgs boson. An estimated sample of more than 20 billion Higgs bosons would allow the absolute determination of its couplings to muons, to photons, to the top quark and to Zγ below the percent level, while di-Higgs production would bring the uncertainty on the Higgs self-coupling below the 5% level. FCC-hh would also significantly advance understanding of the hot QCD medium by enabling lead–lead and other heavy-ion collisions at unprecedented energies, and could be configured to provide electron–proton and electron–ion collisions, says the report.

The FCC-hh design is based on LHC experience and would leverage a substantial amount of the technical infrastructure built for the first FCC stage. Two hadron injector options are under study involving a superconducting machine in either the LHC or SPS tunnel. For the purpose of a technical feasibility analysis, a reference scenario based on 14 T Nb₃Sn magnets cooled to 1.9 K was considered, yielding 2.4 MW of synchrotron radiation and a power consumption of 360 MW or 2.3 TWh/y – a comparable power consumption to FCC-ee.

FCC-hh’s power consumption might be reduced below 300 MW if the magnet temperature can be raised to 4.5 K. Outlining the potential use of high-
temperature superconductors for 14 to 20 T dipole magnets operating at temperatures between 4.5 K and 20 K, the report notes that such technology could either extend the centre-of-mass energy of FCC-hh to 120 TeV or lead to significantly improved operational sustainability at the same collision energy. “The time window of more than 25 years opened by the lepton-collider stage is long enough to bring that technology to market maturity,” says FCC study leader Michael Benedikt  (CERN). “High-temperature superconductors have significant potential for industrial and societal applications, and particle accelerators can serve as pilots for market uptake, as was the case with the Tevatron and the LHC for NbTi technology.”

Society and sustainability

The report details the concepts and paths to keep the FCC’s environmental footprint low while boosting new technologies to benefit society and developing territorial synergies such as energy reuse. The civil construction process for FCC-ee, which would also serve FCC-hh, is estimated to result in about 500,000 tCO2(eq) over a period of 10 years, which the authors say corresponds to approximately one-third of the carbon budget of the Paris Olympic Games. A socio-economic impact assessment of the FCC integrating environmental aspects throughout its entire lifecycle reveals a positive cost–benefit ratio, even under conservative assumptions and adverse implementation conditions.

The actual journey towards the realisation of the FCC starts now

A major achievement of the FCC feasibility study has been the development of the layout and placement of the collider ring and related infrastructure, which have been optimised for scientific benefit while taking into account territorial compatibility, environmental and construction constraints, and cost. No fewer than 100 scenarios were developed and analysed before settling on the preferred option: a ring circumference of 90.7 km with shaft depths ranging between 200 and 400 m, with eight surface sites and four experiments. Throughout the study, CERN has been accompanied by its host states, France and Switzerland, working with entities at the local, regional and national levels to ensure a constructive dialogue with territorial stakeholders.

The final report of the FCC feasibility study together with numerous referenced technical documents have been submitted to the ongoing ESPP 2026 update, along with studies of alternative projects proposed by the community. The CERN Council may take a decision around 2028.

“After four years of effort, perseverance and creativity, the FCC feasibility study was concluded on 31 March 2025,” says Benedikt. “The actual journey towards the realisation of the FCC starts now and promises to be at least as fascinating as the successive steps that brought us to the present state.”

The post FCC feasibility study complete appeared first on CERN Courier.

Particle-beam technology has wide applications in science and industry. Specifically, high-energy x-ray prod­uction is being investigated for FLASH radiotherapy, 14 MeV neutrons are being produced for fusion energy production, and compact electron accelerators are being built for medical-device sterilisation. In each instance it is critical to guarantee that the particle beam is delivered to the end user with the correct makeup, and also to ensure that secondary particles created from scattering interactions are shielded from technicians and sensitive equipment. There is no precise way to predict the random walk of any individual particle as it encounters materials and alloys of different shapes within a complicated apparatus. Monte Carlo methods simulate the random paths of many millions of independent particles, revealing the tendencies of these particles in aggregate. Assessing shielding effectiveness is particularly challenging computationally, as the very nature of shielding means simulations produce low particle rate.

A common technique for shielding calculations takes these random walk simulations a step further by applying variance reduction techniques. Variance reduction techniques are a way of introducing biases in the simulation in a smart way to increase the number of particles emerging from the shielding, while still staying true to the total conservation of matter. In some regions within the shielding, particles are split into independent “daughter” particles with independent pathways but some common history. They are given a weight value, so the overall flux of particles is kept constant. In this way, it is possible to predict the behaviour of a one-in-a-million event without having to simulate one million particle trajectories. The performance of these techniques is shown in figure 2.

These kinds of simulations take on new importance with the global race to develop fusion reactors for energy production. Materials will be exposed to conditions they’ve never seen before, mere feet from the fusion reactions that sustain stars. It is imperative to understand the neutron flux from fusion reactions and how they affect critical components in the sustained operation of fusion facilities if they are going to operate to meet our ever-growing energy needs. Monte Carlo simulation packages are capable of both distributed memory (MPI) and shared memory (OpenMP) parallel computation on the world’s largest supercomputers, engaging hundreds of thousands of cores at once. This enables simulations of billions of particle histories. Together with variance reduction, these powerful simulation tools enable precise estimation of particle fluxes in even the most deeply shielded regions.

RadiaSoft offers browser-based modelling of neutron radiation transport with parallel computation and variance reduction capabilities running on Sirepo, their browser-based interface. Examples of fusion tokamak simulations can be seen above. RadiaSoft is also available for comprehensive consultation in x-ray production, radiation shielding and dose-delivery simulations across a wide range of applications.

The post Leading the industry in Monte Carlo simulations for accelerator applications appeared first on CERN Courier.

“ELISA gives people who visit CERN a chance to really see how the LHC works,” says Science Gateway’s project leader Patrick Geeraert. “This gives visitors a unique experience: they can actually see a proton beam in real time. It then means they can begin to conceptualise the experiments we do at CERN.”

The model accelerator is inspired by a component of LINAC 4 – the first stage in the chain of accelerators used to prepare beams of protons for experiments at the LHC. Hydrogen is injected into a low-pressure chamber and ionised; a one-metre-long RF cavity accelerates the protons to 2 MeV, which then pass through a thin vacuum-sealed window. In dim light, the protons in the air ionise the gas molecules, producing visible light, allowing members of the public to see the beam’s progress before their very eyes (see “Accelerating education” figure).

ELISA – the Experimental Linac for Surface Analysis – will also be used to analyse the composition of cultural artefacts, geological samples and objects brought in by members of the public. This is an established application of low-energy proton accelerators: for example, a particle accelerator is hidden 15 m below the famous glass pyramids of the Louvre in Paris, though it is almost 40 m long and not freely accessible to the public.

“The proton-beam technique is very effective because it has higher sensitivity and lower backgrounds than electron beams,” explains applied physicist and lead designer Serge Mathot. “You can also perform the analysis in the ambient air, instead of in a vacuum, making it more flexible and better suited to fragile objects.”

For ELISA’s first experiment, researchers from the Australian Nuclear Science Technology Organisation and from Oxford’s Ashmolean Museum have proposed a joint research project about the optimisation of ELISA’s analysis of paint samples designed to mimic ancient cave art. The ultimate goal is to work towards a portable accelerator that can be taken to regions of the world that don’t have access to proton beams.

The post Educational accelerator open to the public appeared first on CERN Courier.

The workshop opened with a review of accelerator operations, supported by input from December’s Joint Accelerator Performance Workshop. Maintaining current performance levels requires an extraordinary effort across all the facilities. Performance data from the ongoing Run 3 shows steady improvements in availability and beam delivery. These results are driven by dedicated efforts from system experts, operations teams and accelerator physicists, all working to ensure excellent performance and high availability across the complex.

Electron clouds parting

Attention is now turning to Run 4 and the High-Luminosity LHC (HL-LHC) era. Several challenges have been identified, including the demand for high-intensity beams, radiofrequency (RF) power limitations and electron-cloud effects. In the latter case, synchrotron-radiation photons strike the beam-pipe walls, releasing electrons which are then accelerated by proton bunches, triggering a cascading electron-cloud buildup. Measures to address these issues will be implemented during Long Shutdown 3 (LS3), ensuring CERN’s accelerators continue to meet the demands of its diverse physics community.

LS3 will be a crucial period for CERN. In addition to the deployment of the HL-LHC and major upgrades to the ATLAS and CMS experiments, it will see a widespread programme of consolidation, maintenance and improvements across the accelerator complex to secure future exploitation over the coming decades.

Progress on the HL-LHC upgrade was reviewed in detail, with a focus on key systems – magnets, cryogenics and beam instrumentation – and on the construction of critical components such as crab cavities. The next two years will be decisive, with significant system testing scheduled to ensure that these technologies meet ambitious performance targets.

Planning for LS3 is already well advan­ced. Coordination between all stakeholders has been key to aligning complex interdependencies, and the experienced teams are making strong progress in shaping a resource-loaded plan. The scale of LS3 will require meticulous coordination, but it also represents a unique opportunity to build a more robust and adaptable accelerator complex for the future. Looking beyond LS3, CERN’s unique accelerator complex is well positioned to support an increasingly diverse physics programme. This diversity is one of CERN’s greatest strengths, offering complementary opportunities across a wide range of fields.

The high demand for beam time at ISOLDE, n_TOF, AD-ELENA and the North and East Areas underscores the need for a well-balanced approach that supports a broad range of physics. The discussions highlighted the importance of balancing these demands while ensuring that the full potential of the accelerator complex is realised.

Future opportunities such as those highlighted by the Physics Beyond Colliders study will be shaped by discussions being held as part of the update of the European Strategy for Particle Physics (ESPP). Defining the next generation of physics programmes entails striking a careful balance between continuity and innovation, and the accelerator community will play a central role in setting the priorities.

A forward-looking session at the workshop focused on the Future Circular Collider (FCC) Feasibility Study and the next steps. The physics case was presented alongside updates on territorial implementation and civil-engineering investigations and plans. How the FCC-ee injector complex would fit into the broader strategic picture was examined in detail, along with the goals and deliverables of the pre-technical design report (pre-TDR) phase that is planned to follow the Feasibility Study’s conclusion.

While the FCC remains a central focus, other future projects were also discussed in the context of the ESPP update. These include mature linear-collider proposals, the potential of a muon collider and plasma wakefield acceleration. Development of key technologies, such as high-field magnets and superconducting RF systems, will underpin the realisation of future accelerator-based facilities.

The next steps – preparing for Run 4, implementing the LS3 upgrade programmes and laying the groundwork for future projects – are ambitious but essential. CERN’s future will be shaped by how well we seize these opportunities.

The shared expertise and dedication of CERN’s personnel, combined with a clear strategic vision, provide a solid foundation for success. The path ahead is challenging, but with careful planning, collaboration and innovation, CERN’s accelerator complex will remain at the heart of discovery for decades to come.

The post Chamonix looks to CERN’s future appeared first on CERN Courier.

On the accelerator side, one of the most impactful upgrades will be the brand-new final focusing systems just before the proton or ion beams arrive at the interaction points. In the new “inner triplets”, particles will slalom in a more focused and compacted way than ever before towards collisions inside the detectors.

To achieve the required focusing strength, the new quadrupole magnets will use Nb₃Sn conductors for the first time in an accelerator. Nb₃Sn will allow fields as high as 11.5 T, compared to 8.5 T for the conventional NbTi bending magnets used elsewhere in the LHC. As they are a new technology, an integrated test stand of the full 60 m-long inner-triplet assembly is essential – and work is now in full swing.

Learning opportunity

“The main challenge at this stage is the interconnections between the magnets, particularly the interfaces between the magnets and the cryogenic line,” explains Marta Bajko, who leads work on the inner-triplet-string test facility. “During this process, we have encountered nonconformities, out-of-tolerance components, and other difficulties – expected challenges given that these connections are being made for the first time. This phase is a learning opportunity for everyone involved, allowing us to refine the installation process.”

The last magnet – one of two built in the US – is expected to be installed in May. Before then, the so-called N lines, which enable the electrical connections between the different magnets, will be pulled through the entire magnet chain to prepare for splicing the cables together. Individual system tests and short-circuit tests have already been successfully performed and a novel alignment system developed for the HL-LHC is being installed on each magnet. Mechanical transfer function measurements of some magnets are ongoing, while electrical integrity tests in a helium environment have been successfully completed, along with the pressure and leak test of the superconducting link.

“Training the teams is at the core of our focus, as this setup provides the most comprehensive and realistic mock-up before the installations are to be done in the tunnel,” says Bajko. “The surface installation, located in a closed and easily accessible building near the teams’ workshops and laboratories, offers an invaluable opportunity for them to learn how to perform their tasks effectively. This training often takes place alongside other teams, under real installation constraints, allowing them to gain hands-on experience in a controlled yet authentic environment.”

The inner triplet string is composed of a separation and recombination dipole, a corrector-package assembly and a quadrupole triplet. The dipole combines the two counter-rotating beams into a single channel; the corrector package fine-tunes beam parameters; and the quadrupole triplet focuses the beam onto the interaction point.

Quadrupole triplets have been a staple of accelerator physics since they were first implemented in the early 1950s at synchrotrons such as the Brookhaven Cosmotron and CERN’s Proton Synchrotron. Quadrupole magnets are like lenses that are convex (focusing) in one transverse plane and concave (defocusing) in the other, transporting charged particles like beams of light on an optician’s bench. In a quadrupole triplet, the focusing plane alternates with each quadrupole magnet. The effect is to precisely focus the particle beams onto tight spots within the LHC experiments, maximising the number of particles that interact, and increasing the statistical power available to experimental analyses.

Nb₃Sn is strategically important because it lays the foundation for future high-energy colliders

Though quadrupole triplets are a time-honoured technique, Nb₃Sn brings new challenges. The HL-LHC magnets are the first accelerator magnets to be built at lengths of up to 7 m, and the technical teams at CERN and in the US collaboration – each of which is responsible for half the total “cold mass” production – have decided to produce two variants, primarily driven by differences in available production and testing infrastructure.

Since 2011, engineers and accelerator physicists have been hard at work designing and testing the new magnets and their associated powering, vacuum, alignment, cryogenic, cooling and protection systems. Each component of the HL-LHC will be individually tested before installation in the LHC tunnel, however, this is only half the story as all components must be integrated and operated within the machine, where they will all share a common electrical and cooling circuit. Throughout the rest of 2025, the inner-triplet string will test the integration of all these components, evaluating them in terms of their collective behaviour, in preparation for hardware commissioning and nominal operation.

“We aim to replicate the operational processes of the inner-triplet string using the same tools planned for the HL-LHC machine,” says Bajko. “The control systems and software packages are in an advanced stage of development, prepared through extensive collaboration across CERN, involving three departments and nine equipment groups. The inner-triplet-string team is coordinating these efforts and testing them as if operating from the control room – launching tests in short-circuit mode and verifying system performance to provide feedback to the technical teams and software developers. The test programme has been integrated into a sequencer, and testing procedures are being approved by the relevant stakeholders.”

Return on investment

While Nb₃Sn offers significant advantages over NbTi, manufacturing magnets with it presents several challenges. It requires high-temperature heat treatment after winding, and is brittle and fragile, making it more difficult to handle than the ductile NbTi. As the HL-LHC Nb₃Sn magnets operate at higher current and energy densities, quench protection is more challenging, and the possibility of a sudden loss of superconductivity requires a faster and more robust protection system.

The R&D required to meet these challenges will provide returns long into the future, says Susana Izquierdo Bermudez, who is responsible at CERN for the new HL-LHC magnets.

“CERN’s investment in R&D for Nb₃Sn is strategically important because it lays the foundation for future high-energy colliders. Its increased field strength is crucial for enabling more powerful focusing and bending magnets, allowing for higher beam energies and more compact accelerator designs. This R&D also strengthens CERN’s expertise in advanced superconducting materials and technology, benefitting applications in medical imaging, energy systems and industrial technologies.”

The inner-triplet string will remain an installation on the surface at CERN and is expected to operate until early 2027. Four identical assemblies will be installed underground in the LHC tunnel from 2028 to 2029, during Long Shutdown 3. They will be located 20 m away on either side of the ATLAS and CMS interaction points.

The post CERN gears up for tighter focusing appeared first on CERN Courier.

What motivates you to be CERN’s next Director-General?

CERN is an incredibly important organisation. I believe my deep passion for particle physics, coupled with the experience I have accumulated in recent years, including leading the Deep Underground Neutrino Experiment, DUNE, through a formative phase, and running the Science and Technology Facilities Council in the UK, has equipped me with the right skill set to lead CERN though a particularly important period.

How would you describe your management style?

That’s a good question. My overarching approach is built around delegating and trusting my team. This has two advantages. First, it builds an empowering culture, which in my experience provides the right environment for people to thrive. Second, it frees me up to focus on strategic planning and engagement with numerous key stakeholders. I like to focus on transparency and openness, to build trust both internally and externally.

How will you spend your familiarisation year before you take over in 2026?

First, by getting a deep understanding of CERN “from within”, to plan how I want to approach my mandate. Second, by lending my voice to the scientific discussion that will underpin the third update to the European strategy for particle physics. The European strategy process is a key opportunity for the particle-physics community to provide genuine bottom-up input and shape the future. This is going to be a really varied and exciting year.

What open question in fundamental physics would you most like to see answered in your lifetime?

I am going to have to pick two. I would really like to understand the nature of dark matter. There are a wide range of possibilities, and we are addressing this question from multiple angles; the search for dark matter is an area where the collider and non-collider experiments can both contribute enormously. The second question is the nature of the Higgs field. The Higgs boson is just so different from anything else we’ve ever seen. It’s not just unique – it’s unique and very strange. There are just so many deep questions, such as whether it is fundamental or composite. I am confident that we will make progress in the coming years. I believe the High-Luminosity LHC will be able to make meaningful measurements of the self-coupling at the heart of the Higgs potential. If you’d asked me five years ago whether this was possible, I would have been doubtful. But today I am very optimistic because of the rapid progress with advanced analysis techniques being developed by the brilliant scientists on the LHC experiments.

What areas of R&D are most in need of innovation to meet our science goals?

Artificial intelligence is changing how we look at data in all areas of science. Particle physics is the ideal testing ground for artificial intelligence, because our data is complex there are none of the issues around the sensitive nature of the data that exist in other fields. Complex multidimensional datasets are where you’ll benefit the most from artificial intelligence. I’m also excited by the emergence of new quantum technologies, which will open up fresh opportunities for our detector systems and also new ways of doing experiments in fundamental physics. We’ve only scratched the surface of what can be achieved with entangled quantum systems.

How about in accelerator R&D?

There are two areas that I would like to highlight: making our current technologies more sustainable, and the development of high-field magnets based on high-temperature superconductivity. This connects to the question of innovation more broadly. To quote one example among many, high-temperature superconducting magnets are likely to be an important component of fusion reactors just as much as particle accelerators, making this a very exciting area where CERN can deploy its engineering expertise and really push that programme forward. That’s not just a benefit for particle physics, but a benefit for wider society.

How has CERN changed since you were a fellow back in 1994?

The biggest change is that the collider experiments are larger and more complex, and the scientific and technical skills required have become more specialised. When I first came to CERN, I worked on the OPAL experiment at LEP – a collaboration of less than 400 people. Everybody knew everybody, and it was relatively easy to understand the science of the whole experiment.

My overarching approach is built around delegating and trusting my team

But I don’t think the scientific culture of CERN and the particle-physics community has changed much. When I visit CERN and meet with the younger scientists, I see the same levels of excitement and enthusiasm. People are driven by the wonderful mission of discovery. When planning the future, we need to ensure that early-career researchers can see a clear way forward with opportunities in all periods of their career. This is essential for the long-term health of particle physics. Today we have an amazing machine that’s running beautifully: the LHC. I also don’t think it is possible to overstate the excitement of the High-Luminosity LHC. So there’s a clear and exciting future out to the early 2040s for today’s early-career researchers. The question is what happens beyond that? This is one reason to ensure that there is not a large gap between the end of the High-Luminosity LHC and the start of whatever comes next.

Should the world be aligning on a single project?

Given the increasing scale of investment, we do have to focus as a global community, but that doesn’t necessarily mean a single project. We saw something similar about 10 years ago when the global neutrino community decided to focus its efforts on two complementary long-baseline projects, DUNE and Hyper-Kamiokande. From the perspective of today’s European strategy, the Future Circular Collider (FCC) is an extremely appealing project that would map out an exciting future for CERN for many decades. I think we’ll see this come through strongly in an open and science-driven European strategy process.

How do you see the scientific case for the FCC?

For me, there are two key points. First, gaining a deep understanding of the Higgs boson is the natural next step in our field. We have discovered something truly unique, and we should now explore its properties to gain deeper insights into fundamental physics. Scientifically, the FCC provides everything you want from a Higgs factory, both in terms of luminosity and the opportunity to support multiple experiments.

Second, investment in the FCC tunnel will provide a route to hadron–hadron collisions at the 100 TeV scale. I find it difficult to foresee a future where we will not want this capability.

These two aspects make the FCC a very attractive proposition.

How successful do you believe particle physics is in communicating science and societal impacts to the public and to policymakers?

I think we communicate science well. After all, we’ve got a great story. People get the idea that we work to understand the universe at its most basic level. It’s a simple and profound message.

Going beyond the science, the way we communicate the wider industrial and societal impact is probably equally important. Here we also have a good story. In our experiments we are always pushing beyond the limits of current technology, doing things that have not been done before. The technologies we develop to do this almost always find their way back into something that will have wider applications. Of course, when we start, we don’t know what the impact will be. That’s the strength and beauty of pushing the boundaries of technology for science.

Would the FCC give a strong return on investment to the member states?

Absolutely. Part of the return is the science, part is the investment in technology, and we should not underestimate the importance of the training opportunities for young people across Europe. CERN provides such an amazing and inspiring environment for young people. The scale of the FCC will provide a huge number of opportunities for young scientists and engineers.

We need to ensure that early-career researchers can see a clear way forward with opportunities in all periods of their career. This is essential for the long-term health of particle physics

In terms of technology development, the detectors for the electron–positron collider will provide an opportunity for pushing forward and deploying new, advanced technologies to deliver the precision required for the science programme. In parallel, the development of the magnet technologies for the future hadron collider will be really exciting, particularly the potential use of high-temperature superconductors, as I said before.

It is always difficult to predict the specific “return on investment” on the technologies for big scientific research infrastructure. Part of this challenge is that some of that benefits might be 20, 30, 40 years down the line. Nevertheless, every retrospective that has tried, has demonstrated that you get a huge downstream benefit.

Do we reward technical innovation well enough in high-energy physics?

There needs to be a bit of a culture shift within our community. Engineering and technology innovation are critical to the future of science and critical to the prosperity of Europe. We should be striving to reward individuals working in these areas.

Should the field make it more flexible for physicists and engineers to work in industry and return to the field having worked there?

This is an important question. I actually think things are changing. The fluidity between academia and industry is increasing in both directions. For example, an early-career researcher in particle physics with a background in deep artificial-intelligence techniques is valued incredibly highly by industry. It also works the other way around, and I experienced this myself in my career when one of my post-doctoral researchers joined from an industry background after a PhD in particle physics. The software skills they picked up from industry were incredibly impactful.

I don’t think there is much we need to do to directly increase flexibility – it’s more about culture change, to recognise that fluidity between industry and academia is important and beneficial. Career trajectories are evolving across many sectors. People move around much more than they did in the past.

Does CERN have a future as a global laboratory?

CERN already is a global laboratory. The amazing range of nationalities working here is both inspiring and a huge benefit to CERN.

How can we open up opportunities in low- and middle-income countries?

I am really passionate about the importance of diversity in all its forms and this includes national and regional inclusivity. It is an agenda that I pursued in my last two positions. At the Deep Underground Neutrino Experiment, I was really keen to engage the scientific community from Latin America, and I believe this has been mutually beneficial. At STFC, we used physics as a way to provide opportunities for people across Africa to gain high-tech skills. Going beyond the training, one of the challenges is to ensure that people use these skills in their home nations. Otherwise, you’re not really helping low- and middle-income countries to develop.

What message would you like to leave with readers?

That we have really only just started the LHC programme. With more than a factor of 10 increase in data to come, coupled with new data tools and upgraded detectors, the High-Luminosity LHC represents a major opportunity for a new discovery. Its nature could be a complete surprise. That’s the whole point of exploring the unknown: you don’t know what’s out there. This alone is incredibly exciting, and it is just a part of CERN’s amazing future.

The post A word with CERN’s next Director-General appeared first on CERN Courier.

The International Muon Collider Collaboration (IMCC), supported by the EU MuCol study, is working to assess the potential of a muon collider as a future facility, along with the R&D needed to make it a reality. European engagement in this effort crystalised following the 2020 update to the European Strategy for Particle Physics (ESPPU), which identified the development of bright muon beams as a high-priority initiative. Worldwide interest in a muon collider is quickly growing: the 2023 Particle Physics Project Prioritization Panel (P5) recently identified it as an important future possibility for the US particle-physics community; Japanese colleagues have proposed a muon-collider concept, muTRISTAN (CERN Courier July/August 2024 p8); and Chinese colleagues have actively contributed to IMCC efforts as collaboration members.

Lighting the way

The workshop focused on reviewing the scope and design progress of a muon-cooling demonstrator facility, identifying potential host sites and timelines, and exploring science programmes that could be developed alongside it. Diktys Stratakis (Fermilab) began by reviewing the requirements and challenges of muon cooling. Delivering a high-brightness muon beam will be essential to achieving the luminosity needed for a muon collider. The technique proposed for this is ionisation cooling, wherein the phase-space volume of the muon beam decreases as it traverses a sequence of cells, each containing an energy- absorbing mat­erial and accelerating radiofrequency (RF) cavities.

Roberto Losito (CERN) called for a careful balance between ambition and practicality – the programme must be executed in a timely way if a muon collider is to be a viable next-generation facility. The Muon Cooling Demonstrator programme was conceived to prove that this technology can be developed, built and reliably operated. This is a critical step for any muon-collider programme, as highlighted in the ESPPU–LDG Accelerator R&D Roadmap published in 2022. The plan is to pursue a staged approach, starting with the development of the magnet, RF and absorber technology, and demonstrating the robust operation of high-gradient RF cavities in high magnetic fields. The components will then be integrated into a prototype cooling cell. The programme will conclude with a demonstration of the operation of a multi-cell cooling system with a beam, building on the cooling proof of principle made by the Muon Ionisation Cooling Experiment.

Chris Rogers (STFC RAL) summarised an emerging consensus that it is critical to demonstrate the reliable operation of a cooling lattice formed of multiple cells. While the technological complexity of the cooling-cell prototype will undergo further review, the preliminary choice presents a moderately challenging performance that could be achieved within five to seven years with reasonable investment. The target cooling performance of a whole cooling lattice remains to be established and depends on future funding levels. However, delegates agreed that a timely demonstration is more important than an ambitious cooling target.

Worldwide interest in a muon collider is quickly growing

The workshop also provided an opportunity to assess progress in designing the cooling-cell prototype. Given that the muon beam originates from hadron decays and is initially the size of a watermelon, solenoid magnets were chosen as they can contain large beams in a compact lattice and provide focusing in both horizontal and vertical planes simultaneously. Marco Statera (INFN LASA) presented preliminary solutions for the solenoid coil configuration based on high-temperature superconductors operating at 20 K: the challenge is to deliver the target magnetic field profile given axial forces, coil stresses and compact integration.

In ionisation cooling, low-Z absorbers are used to reduce the transverse momenta of the muons while keeping the multiple scattering at manageable levels. Candidate materials are lithium hydride and liquid hydrogen. Chris Rogers discussed the need to test absorbers and containment windows at the highest intensities. The potential for performance tests using muons or intensity tests using another particle species such as protons was considered to verify understanding of the collective interaction between the beam and the absorber. RF cavities are required to replace longitudinal energy lost in the absorbers.  Dario Giove (INFN LASA) introduced the prototype of an RF structure based on three coupled 704 MHz cavities and presented a proposal to use existing INFN capabilities to carry out a test programme for materials and cavities in magnetic fields. The use of cavity windows was also discussed, as it would enable greater accelerating gradients, though at the cost of beam degradation, increased thermal loads and possible cavity detuning. The first steps in integ­rating these latest hardware designs into a compact cooling cell were presented by Lucio Rossi (INFN LASA and UMIL). Future work needs to address the management of the axial forces and cryogenic heat loads, Rossi observed.

Many institutes presented a strong interest in contributing to the programme, both in the hardware R&D and hosting the eventual demonstrator. The final sessions of the workshop focused on potential host laboratories.

The event underscored the critical need for sustained innovation, timely implementation and global cooperation

At CERN, two potential sites were discussed, with ongoing studies focusing on the TT7 tunnel, where a moderate-power 10 kW proton beam from the Proton Synchrotron could be used for muon production. Preliminary beam physics studies of muon beam production and transport are already underway. Lukasz Krzempek (CERN) and Paul Jurj (Imperial College London) presented the first integration and beam-physics studies of the demonstrator facility in the TT7 tunnel, highlighting civil engineering and beamline design requirements, logistical challenges and safety considerations, finding no apparent showstoppers.

Jeff Eldred (Fermilab) gave an overview of Fermilab’s broad range of candidate sites and proton-beam energies. While further feasibility studies are required, Eldred highlighted that using 8 GeV protons from the Booster is an attractive option due to the favourable existing infrastructure and its alignment with Fermilab’s muon-collider scenario, which envisions a proton driver based on the same Booster proton energy.

The Fermilab workshop represented a significant milestone in advancing the Muon Cooling Demonstrator, highlighting enthusiasm from the US community to join forces with the IMCC and growing interest in Asia. As Mark Palmer (BNL) observed in his closing remarks, the event underscored the critical need for sustained innovation, timely implementation and global cooperation to make the muon collider a reality.

The post Muon cooling kickoff at Fermilab appeared first on CERN Courier.

Out of more than 30 presentations, a significant number featured pulsed, high-peak-power RF sources working at frequencies above 3 GHz in the S, C and X bands. These involve high-efficiency klystrons that are being designed, built and tested for the KEK e^–/e⁺ Injector, the new EuPRAXIA@SPARC_LAB linac, the CLIC testing facilities, muon collider R&D, the CEPC injector linac and the C³ project. Reported increases in beam-to-RF power efficiency range from 15 percentage points for the retro­fit prototype for CLIC to more than 25 points (expected) for a new greenfield klystron design that can be used across most new projects.

A very dynamic area for R&D is the search of efficient sources for the continuous wave (CW) and long-pulse RF needed for circular accelerators. Typically working in the L-band, existing devices deliver less than 3 MW in peak power. Solid-state amplifiers, inductive output tubes, klystrons, magnetrons, triodes and exotic newly rediscovered vacuum tubes called “tristrons” compete in this arena. Successful prototypes have been built for the High-Luminosity LHC and CEPC with power efficiency gains of 10 to 20 points. In the case of the LHC, this will allow 15% more power without an impact on the electricity bill; in the case of a circular Higgs factory, this will allow a 30% reduction. CERN and SLAC are also investigating very-high-efficiency vacuum tubes for the Future Circular Collider with a potential reduction of close to 50% on the final electricity bill. A collaboration between academia and industry would certainly be required to bring this exciting new technology to light.

Besides the astounding advances in vacuum-tube technology, solid-state amplifiers based on cheap transistors are undergoing a major transformation thanks to the adoption of gallium-nitride technology. Commercial amplifiers are now capable of delivering kilowatts of power at low duty cycles with a power efficiency of 80%, while Uppsala University and the European Spallation Source have demonstrated the same efficiency for combined systems working in CW.

The search for energy efficiency does not stop at designing and building more efficient RF sources. All aspects of operation, power combination and using permanent magnets and efficient modulators need to be folded in, as described by many concrete examples during the workshop. The field is thriving.

The post Unprecedented progress in energy-efficient RF appeared first on CERN Courier.

The committee heard extensive reports from the leading HEP laboratories and various world regions on their recent activities and plans, including a presentation by Paris Sphicas, the chair of the European Committee for Future Accelerators (ECFA), on the process for the update of the European strategy for particle physics (ESPP). Launched by CERN Council in March 2024, the ESPP update is charged with recommending the next collider project at CERN after HL-LHC operation.

A global task

The ESPP update is also of high interest to non-European institutions and projects. Consequently, in addition to the expected inputs to the strategy from European HEP communities, those from non-European HEP communities are also welcome. Moreover, the recent US P5 report and the Chinese plans for CEPC, with a potential positive decision in 2025/2026, and discussions about the ILC project in Japan, will be important elements of the work to be carried out in the context of the ESPP update. They also emphasise the global nature of high-energy physics.

An integral part of the work of ICFA is carried out within its panels, which have been very active. Presentations were given from the new panel on the Data Lifecycle (chair Kati Lassila-Perini, Helsinki), the Beam Dynamics panel (new chair Yuan He, IMPCAS) and the Advanced and Novel Accelerators panel (new chair Patric Muggli, Max Planck Munich, proxied at the meeting by Brigitte Cros, Paris-Saclay). The Instrumentation and Innovation Development panel (chair Ian Shipsey, Oxford) is setting an example with its numerous schools, the ICFA instrumentation awards and centrally sponsored instrumentation studentships for early-career researchers from underserved world regions. Finally, the chair of the ILC International Development Team panel (Tatsuya Nakada, EPFL) summarised the latest status of the ILC Technological Network, and the proposed ILC collider project in Japan.

ICFA noted interesting structural developments in the global organisation of HEP

A special session was devoted to the sustainability of HEP accelerator infrastructures, considering the need to invest efforts into guidelines that enable better comparison of the environmental reports of labs and infrastructures, in particular for future facilities. It was therefore natural for ICFA to also hear reports not only from the panel on Sustainable Accelerators and Colliders led by Thomas Roser (BNL), but also from the European Lab Directors Working Group on Sustainability. This group, chaired by Caterina Bloise (INFN) and Maxim Titov (CEA), is mandated to develop a set of key indicators and a methodology for the reporting on future HEP projects, to be delivered in time for the ESPP update.

Finally, ICFA noted some very interesting structural developments in the global organisation of HEP. In the Asia-Oceania region, ACFA-HEP was recently formed as a sub-panel under the Asian Committee for Future Accelerators (ACFA), aiming for a better coordination of HEP activities in this particular region of the world. Hopefully, this will encourage other world regions to organise themselves in a similar way in order to strengthen their voice in the global HEP community – for example in Latin America. Here, a meeting was organised in August by the Latin American Association for High Energy, Cosmology and Astroparticle Physics (LAA-HECAP) to bring together scientists, institutions and funding agencies from across Latin America to coordinate actions for jointly funding research projects across the continent.

The next in-person ICFA meeting will be held during the Lepton–Photon conference in Madison, Wisconsin (USA), in August 2025.

The post ICFA talks strategy and sustainability in Prague appeared first on CERN Courier.

Brüning and Rossi’s book offers a comprehensive overview of this work across 31 chapters authored by more than 150 contributors. Due to the mentioned complexity of the HL-LHC, it is advisable to read the excellent introductory chapter first to obtain an overview on the various physics aspects, different components and project structure. After coverage of the physics case and the upgrades to the LHC experiments, the operational experiences with the LHC and its performance development are described.

The LHC’s upgrade is a significant project, as evidenced by the involvement of nine collaborating countries including China and the US, a materials budget that exceeds one billion Swiss Francs, more than 2200 years of integrated work, and the complexity of the physics and engineering. The safe operation of the enormous beam intensity represented a major challenge for the original LHC, and will be even more challenging with the upgraded beam parameters. For example, the instantaneous power carried by the circulating beam will be 7.6 TW, while the total beam energy is then 680 MJ – enough energy to boil two tonnes of water. Such numbers should be compared with the extremely low power density of 30 mW/cm³, which is sufficient to quench a superconducting magnet coil and interrupt the operation of the entire facility.

The book continues with descriptions of the two subsystems of greatest importance for the luminosity increase: the superconducting magnets and the RF systems including the crab cavities.

Besides the increase in intensity, the primary factor for instantaneous luminosity gain is obtained by a reduction in beam size at the interaction points (IPs), partly through a smaller emittance but mainly through improved beam optics. This change results in a larger beam in the superconducting quadrupoles beside the IP. To accommodate the upgraded beam and to shield the magnet coils from radiation, the aperture of these magnets is increased by more than a factor of two to 150 mm. New quadrupoles have been developed, utilising the superconductor material Nb₃Sn, allowing higher fields at the location of the coils. Further measures include the cancellation of the beam crossing angle during collision by dynamic tilting of the bunch orientation using the superconducting crab cavities that were designed for this special application in the LHC. The authors make fascinating observations, for example regarding the enhanced sensitivity to errors due to the extreme beam demagnification at the IPs: a typical relative error of 10^–4 in the strength of the IP quadrupoles results in a significant distortion in beam optics, a so-called beta-beat of 7%.

Chapter eight describes the upgrade to the beam-collimation system, which is of particular importance for the safe operation of high-intensity beams. For ion collimation, halo particles are extracted most efficiently using collimators made from bent crystals.

The book continues with a description of the magnet-powering circuits. For the new superconducting magnets CERN is using “superconducting links” for the first time: cable sets made of a high-temperature superconductor that can carry enormous currents on many circuits in parallel in a small cross section; it suffices to cool them to temperatures of around 20 to 30K with gaseous helium by evaporating some of the liquid helium that is used for cooling the superconducting magnets in the accelerator.

Magnetic efforts

The next chapters cover machine protection, the interface with the detectors and the cryogenic system. Chapter 15 is dedicated to the effects of beam-induced stray radiation, in particular on electronics – an effect that has become quite important at high intensities in recent years. Another chapter covers the development of an 11 Tesla dipole magnet that was intended to replace a regular superconducting magnet, thereby gaining space for additional collimators in the arc of the ring. Despite considerable effort, this programme was eventually dropped from the project because the new magnet technology could not be mastered with the required reliability for routine operation; and, most importantly, alternative collimation solutions were identified.

Other chapters describe virtually all the remaining technical subsystems and beam-dynamics aspects of the collider, as well as the extensive test infrastructure required before installation in the LHC. A whole chapter is dedicated to high-field-magnet R&D – a field of utmost importance to the development of a next-generation hadron collider beyond the LHC.

Brüning and Rossi’s book will interest accelerator physicists in that it describes many outstanding beam-physics aspects of the HL-LHC. Engineers and readers with an interest in technology will also find many technical details on its subsystems.

The post Intensely focused on physics appeared first on CERN Courier.

SLAC and LBNL directors John Sarrao and Mike Witherell opened the meeting by emphasising the vital roles of international collaboration between national laboratories in advancing scientific discovery. Sarrao highlighted SLAC’s historical contributions to high-energy physics and expressed enthusiasm for the FCC’s scientific potential. Witherell reflected on the legacy of particle accelerators in fundamental science and the importance of continued innovation.

CERN Director-General Fabiola Gianotti identified three pillars of her vision for the laboratory: flagship projects like the LHC; a diverse complementary scientific programme; and preparations for future projects. She identified the FCC as the best future match for this vision, asserting that it has unparalleled potential for discovering new physics and can accommodate a large and diverse scientific community. “It is crucial to design a facility that offers a broad scientific programme, many experiments and exciting physics to attract young talents,” she said.

International collaboration, especially with the US, is important in ensuring the project’s success

FCC-ee would operate at several centre-of-mass energies corresponding to the Z-boson pole, W-boson pair-production, Higgs-boson pole or top-quark pair production. The beam current at each of these points would be determined by the design value of 50 MW synchrotron-radiation power per beam. At lower energies, the machine could accommodate more bunches, achieving 1.3 amperes and a luminosity in excess of 10³⁶ cm^–2 s^–1 at the Z pole. Measurements of electroweak observables and Higgs-boson couplings would be improved by a factor of between 10 and 50. Remarkably, FCC-ee would also provide 10 times the ambitious design statistics of SuperKEKB/Belle II for bottom and charm quarks, making it the world-leading machine at the intensity frontier. Along with other measurements of electroweak observables, FCC-ee will indirectly probe energies up to 70 TeV for weakly interacting particles. Unlike at proposed linear colliders, four interaction points would increase scientific robustness, reduce systematic uncertainties and allow for specialised experiments, maximising the collider’s physics output.

For FCC-hh, two approaches are being pursued for the necessary high-field superconducting magnets. The first involves advancing niobium–tin technology, which is currently mastered at 11–12 T for the High-Luminosity LHC, with the goal of reaching operational fields of 14 T. The second focuses on high-temperature superconductors (HTS) such as REBCO and iron-based superconductors (IBS). REBCO comes mainly in tape form (CERN Courier May/June 2023 p37), whereas IBS comes in both tape and wire form. With niobium-tin, 14 T would allow proton–proton collision energies of 80 TeV in a 90 km ring. HTS-based magnets could potentially reach fields up to 20 T, and centre-of-mass energies proportionally higher, in the vicinity of 120 TeV. If HTS magnets prove technically feasible, they could greatly decrease the cryogenic power. The development of such technologies also holds great promise beyond fundamental research, for example in transportation and electricity transmission.

FCC study leader Michael Benedikt (CERN) outlined the status of the ongoing feasibility study, which is set to be completed by March 2025. No technical showstoppers have yet been found, paving the way for the next phase of detailed technical and environmental impact studies and critical site investigations. Benedikt stressed the importance of international collaboration, especially with the US, in ensuring the project’s success.

The next step for the FCC project is to provide information to the CERN Council, via the upcoming update of the European strategy for particle physics, to facilitate a decision on whether to pursue the FCC by the end of 2027 or in early 2028. This includes further developing the civil engineering and technical design of major systems and components to present a more detailed cost estimate, continuing technical R&D activities, and working with CERN’s host states on regional implementation development and authorisation processes along with the launch of an environmental impact study. FCC would intersect 31 municipalities in France and 10 in Switzerland. Detailed work is ongoing to identify and reserve plots of land for surface sites, address site-specific design aspects, and explore socio-economic and ecological opportunities such as waste-heat utilisation.

The post FCC builds momentum in San Francisco appeared first on CERN Courier.

“The decision to shift the start of the HL-LHC by approximately one year and increase the length of the shutdown reflects a consensus supported by our scientific committees,” explains Mike Lamont, CERN director for accelerators and technology. “The delayed start of LS3 is primarily due to significant challenges encountered during the Phase II upgrades of the ATLAS and CMS experiments, which have led to the erosion of contingency time and introduced considerable schedule risks. The challenges faced by the experiment teams included COVID-19 and the impact of the Russian invasion of Ukraine.”

LS3 represents a pivotal phase in enhancing CERN’s capabilities. During the shutdown, ATLAS and CMS will replace many of their detectors and a large part of their electronics. Schedule contingencies have been insufficient for the new inner tracker for ATLAS, and for the HGCAL and new tracker for CMS. The delayed start of LS3 will allow the collaborations more time to develop and build these highly sophisticated detectors and systems.

On the machine side, a key activity during LS3 is the drilling of 28 vertical cores to link the new HL-LHC technical galleries to the LHC tunnel. Initially expected to take six months, this timeframe was reduced to two months in 2021 to optimise the schedule. However, challenges encountered during the tendering process and in subsequent consultations with specialists necessitated a return to the original six-month timeline for core excavation.

In addition to high-luminosity enhancements, LS3 will involve a major programme of work across the accelerator complex. This includes the North Area consolidation project and the transformation of the ECN3 cavern into a high-intensity fixed-target facility; the dismantling of the CNGS target to make way for the next phase of wakefield-acceleration research at AWAKE; improvements to ISOLDE to boost the facility’s nuclear-studies potential; and extensive maintenance and consolidation across all machines and facilities to ensure operational safety, longevity and availability.

“All these activities are essential to ensuring the medium-term future of the laboratory and allowing full exploitation of its remarkable potential in the coming decades,” says Lamont.

The post Revised schedule for the High-Luminosity LHC appeared first on CERN Courier.

The committee heard extensive reports from the leading HEP laboratories and various world regions on their recent activities and plans, including a presentation by Paris Sphicas, the chair of the European Committee for Future Accelerators (ECFA), on the process for the update of the European strategy for particle physics (ESPP). Launched by CERN Council in March 2024, the ESPP update is charged with recommending the next collider project at CERN after HL-LHC operation.

A global task

The ESPP update is also of high interest to non-European institutions and projects. Consequently, in addition to the expected inputs to the strategy from European HEP communities, those from non-European HEP communities are also welcome. Moreover, the recent US P5 report and the Chinese plans for CEPC, with a potential positive decision in 2025/2026, and discussions about the ILC project in Japan, will be important elements of the work to be carried out in the context of the ESPP update. They also emphasise the global nature of high-energy physics.

An integral part of the work of ICFA is carried out within its panels, which have been very active. Presentations were given from the new panel on the Data Lifecycle (chair Kati Lassila-Perini, Helsinki), the Beam Dynamics panel (new chair Yuan He, IMPCAS) and the Advanced and Novel Accelerators panel (new chair Patric Muggli, Max Planck Munich, proxied at the meeting by Brigitte Cros, Paris-Saclay). The Instrumentation and Innovation Development panel (chair Ian Shipsey, Oxford) is setting an example with its numerous schools, the ICFA instrumentation awards and centrally sponsored instrumentation studentships for early-career researchers from underserved world regions. Finally, the chair of the ILC International Development Team panel (Tatsuya Nakada, EPFL) summarised the latest status of the ILC Technological Network, and the proposed ILC collider project in Japan.

ICFA noted interesting structural developments in the global organisation of HEP

A special session was devoted to the sustainability of HEP accelerator infrastructures, considering the need to invest efforts into guidelines that enable better comparison of the environmental reports of labs and infrastructures, in particular for future facilities. It was therefore natural for ICFA to also hear reports not only from the panel on Sustainable Accelerators and Colliders led by Thomas Roser (BNL), but also from the European Lab Directors Working Group on Sustainability. This group, chaired by Caterina Bloise (INFN) and Maxim Titov (CEA), is mandated to develop a set of key indicators and a methodology for the reporting on future HEP projects, to be delivered in time for the ESPP update.

Finally, ICFA noted some very interesting structural developments in the global organisation of HEP. In the Asia-Oceania region, ACFA-HEP was recently formed as a sub-panel under the Asian Committee for Future Accelerators (ACFA), aiming for a better coordination of HEP activities in this particular region of the world. Hopefully, this will encourage other world regions to organise themselves in a similar way in order to strengthen their voice in the global HEP community – for example in Latin America. Here, a meeting was organised in August by the Latin American Association for High Energy, Cosmology and Astroparticle Physics (LAA-HECAP) to bring together scientists, institutions and funding agencies from across Latin America to coordinate actions for jointly funding research projects across the continent.

The next in-person ICFA meeting will be held during the Lepton–Photon conference in Madison, Wisconsin (USA), in August 2025.

The post ICFA talks strategy and sustainability in Prague appeared first on CERN Courier.

The sole material suitable for the beam pipes at the heart of the LHC experiments is beryllium — a substance used in only few other domains, such as the aerospace industry. Its low atomic number (Z = 4) leads to minimal interaction with high-energy particles, reducing scattering and energy loss. The only solid element with a lower atomic number is lithium (Z = 3), but it cannot be used as it oxidizes rapidly and reacts violently with moisture, producing flammable hydrogen gas. Despite being less dense than aluminium, beryllium is six times stronger than steel, and can withstand the mechanical stresses and thermal loads encountered during collider operations. Beryllium also has good thermal conductivity, which helps dissipate the heat generated during beam collisions, preventing the beam pipe from overheating.

But beryllium also has drawbacks. It is expensive to procure as it comes in the form of a powder that must be compressed at very high pressure to obtain metal rods, and as beryllium is toxic, all manufacturing steps require strict safety procedures.

By bringing beam-pipe production in-house, CERN will acquire unique expertise

The last supplier worldwide able to machine and weld beryllium beam pipes within the strict tolerances required by the LHC experiments decided to discontinue their production in 2023. Given the need for multiple new beam pipes as part of the forthcoming high-luminosity upgrade to the LHC (HL-LHC), CERN has decided to build a new facility to manufacture vacuum pipes on site, including parts made of beryllium. A 650 m² workshop is scheduled to begin operations on CERN’s Prévessin site next year.

By insourcing beryllium beam-pipe production, CERN will gain direct control of the manufacturing process, allowing stricter quality assurance and greater flexibility to meet changing experimental requirements. The new facility will include several spaces to perform metallurgical analysis, machining of components, surface treatments, final assembly by electron-beam welding, and quality control steps such as metrology and non-destructive tests. As soon as beryllium beampipes are fabricated, they will follow the usual steps for ultra-high vacuum conditioning that are already available in CERN’s facilities. These include helium leak tests, non-evaporable-getter thin-film coatings, the installation of bakeout equipment, and final vacuum assessments.

Once the new workshop is operational, the validation of the different manufacturing processes will continue until mid-2026. Production will then begin for new beam pipes for the ALICE, ATLAS and CMS experiments in time for the HL-LHC, as each experiment will replace their pixel tracker – the sub-detector closest to the beam – and therefore require a new vacuum chamber. With stricter manufacturing requirements, never accomplishment before now, and a conical section designed to maximise transparency in the forward regions where particles pass through at smaller angles, ALICE’s vacuum chamber will pose a particular challenge. Together totalling 21 m in length, the first three beam pipes to be constructed at CERN will be installed in the detectors during the LHC’s Long Shutdown 3 from 2027 to 2028.

By bringing beam-pipe production in-house, CERN will acquire unique expertise that will be useful not only for the HL-LHC experiments, but also for future projects and other accelerators around the world, and preserve a fundamental technology for experimental beam pipes.

The post CERN to insource beam-pipe production appeared first on CERN Courier.

Today, around 5000 accelerator scientists and engineers work in more than 50 countries, collaborating with a pool of technical experts three to four times that size. While most are deeply involved in operations and upgrades, their careers also include designing and constructing new facilities, beam-physics research, developing critical technical components, and project leadership. Their work often involves technology transfer, industrial applications, education and training of future experts, and public and academic outreach.

A global field

The need for regular meetings of the entire field has long been recognised. Historically, regional conferences like the biannual particle-accelerator conferences (PACs) in the US (1965–2009), the biannual EPACs in Europe (1988–2008) and the triannual APACs in Asia (1998–2007) served this purpose. These gatherings covered all types of accelerators, particles and use-cases. As the field became truly global, leaders established the series of international PACs (IPACs), which rotate through the regions in a three-year cycle, convening about 1500 attendees. The 15th IPAC took place from 19 to 24 May in Nashville, Tennessee, with almost 200 registrants from Asia, more than 400 from Europe and nearly 700 from the US.

The “beef” of the conference was in the reports from facilities, but no one person can summarise all the progress, and I must restrict myself to personal highlights in fields that are close to my heart. Fascinating progress was reported on energy-recovery linacs (ERLs) and associated technologies such as superconducting RF and fixed-field-alternating-gradient accelerators, following the recent success of the CBETA accelerator test facility at Cornell. Another hot topic in my eyes was design work and experimental studies towards strong hadron cooling for the Electron–Ion Collider. This year’s progress in industrial and medical accelerators is also impressive, with noteworthy presentations on radioisotope production and radiotherapy (Oliver Kester, TRIUMF and Michael Galonska, GSI), light sources for semiconductor manufacturing (Bruce Dunham, SLAC), accelerator-driven fusion (Richard Magee, TAE Technologies), and 96 exhibitions from companies and institutions worldwide.

CERN’s FCC-ee project was discussed in several sessions. Nuria Catalan-Lasheras (CERN) gave a memorable talk demonstrating impressive progress on high-power klystrons (RF sources). At present, klystrons have about 55% efficiency – RF power divided by wall-plug power – but she noted that they have the potential to go to as high as about 85% efficiency. The path is clear: increase voltage and decrease current, thereby reducing the “microperveance” of the klystrons. This will be crucial at FCC-ee, which must continuously replenish 100 MW of synchrotron radiation losses with 100 MW of RF power. The klystron efficiency improvement alone can save more than 60 MW – fully a third of the current power consumption of the CERN accelerator complex.

The “beef” of the conference was in the reports from facilities, but no one person can summarise all the progress

Muon colliders were presented as a unique opportunity to achieve a substantial energy increase compared to hadrons (Diktys Stratakis, Fermilab). Due to the point-like nature of the muon, the full centre-of-mass energy is available for probing new physics processes in every collision. Therefore, a 10 TeV muon collider can provide comparable high-energy-physics breakthroughs to a 100 TeV proton–proton collider, where colliding partons only carry a fraction of the proton’s energy. Due to its compactness, the cost of a 10 TeV muon collider compares to that of the FCC-ee and is likely to be many times lower than any other alternative concept that can achieve 10 pCM (parton centre-of-mass) energies (T Roser et al. 2023 JINST 18 P05018). The challenge lies in developing technologies for muon production, cooling and acceleration in the next two decades. In the upcoming 19 to 25 years it should be technically feasible for the accelerator community to demonstrate the technologies of a) high-intensity and short proton bunches; b) high-power proton targets; c) muon cooling; d) fast muon acceleration; e) 10 to 12 T superconducting magnets lined with tungsten inserts to protect coils from the muon decay products, and; f) effective spreading of the narrow cones of ultra-high-energy neutrinos by wiggling the beams, to avoid damage caused by the chargeless neutrinos when the muons decay.

In the conference’s closing talk, I reviewed three dozen future-collider proposals, analysed the ultimate energies potentially attainable in all types of colliding beams and accelerators within reasonable cost and power consumption limits, and laid out arguments that energies beyond a PeV (thousands of TeV) can be achieved, concluding that muons are the particles of the future for high-energy physics.

I can attest to IPAC’s success in fostering real-life interactions in the global accelerator landscape

The prize session was a highlight, with acceptance speeches from KEK’s Kaoru Yokoya (APS Wilson Prize) and SLAC’s Gennady Stupakov (IEEE NPSS PAST Award). Yokoya outlined his participation in various electron–positron machines and proposals such as the TRISTAN e⁺e^– collider and the ILC. Stupakov emphasised the importance of beam-dynamics theory in the age of computer modelling and simulations.

Ever since the first edition in Kyoto in 2010, I can attest to IPAC’s success in fostering real-life interactions in the global accelerator landscape. After the conference, I counted more than a hundred encounters of 5 minutes or more – something that would be difficult to achieve at a smaller or more specialised conference. It was pleasing to see many Chinese colleagues attend this US-based conference, but I did not identify any participants from Russia – a concerning development for our science’s international spirit. I hope political barriers will not interfere with next year’s IPAC’25 in Taiwan.

On a personal note, I would like to thank the organisers for putting together great scientific and social programmes, and the dedicated Joint Accelerator Conferences Website team, whose tireless efforts ensured that virtually all conference proceedings – papers, talks and posters – were available online by the final day, setting a standard that other fields of high-energy physics could greatly benefit from.

The post Music city tunes in to accelerators appeared first on CERN Courier.

Immense effort

Analysing the performance of CERN’s accelerator complex, speakers noted the impressive progress to date, examined limitations in the LHC and injectors and discussed improvements for optimal performance in upcoming runs. It’s difficult to do justice to the immense technical effort made by all systems, operations and technical infrastructure teams that underpins the exploitation of the complex. Machine availability emerged as a crucial theme, recognised as critical for both maximising the potential of existing facilities and ensuring the success of the HL-LHC. Fault tracking, dedicated maintenance efforts and targeted infrastructure improvements across the complex were highlighted as key contributors to achieving and maintaining optimal uptime.

As the HL-LHC project moves into full series production, the technical challenges associated with magnets, cold powering and crab cavities are being addressed (CERN Courier January/February 2024 p37). Looking beyond Long Shutdown 3 (LS3), potential limitations are already being targeted now, with, for example, electron-cloud mitigation measures planned to be deployed in LS3. The transition to the high-luminosity era will involve a huge programme of work that requires meticulous preparation and a well-coordinated effort across the complex during LS3, which will see the deployment of the HL-LHC, a widespread consolidation effort, and other upgrades such as that planned for the ECN3 cavern at CERN’s North Area.

The vision for the next decades of these facilities is diverse, imaginative and well-motivated from a physics perspective

The breadth and depth of the physics being performed at CERN facilities is quite remarkable, and the Chamonix workshop reconfirmed the high demand from experimentalists across the board. The unique capabilities of ISOLDE, n_TOF, AD-ELENA, and the East and North Areas were recognised. The North Area, for example, provides protons, hadrons, electrons and ion beams for detector R&D, experiments, the CERN neutrino platform, irradiation facilities and counts more than 2000 users. The vision for the next decades of these facilities is diverse, imaginative and well-motivated from a physics perspective. The potential for long-term exploitation and leveraging fully the capabilities of the LHC and other facilities is considerable, demanding continued support and development.

In the longer term, CERN is exploring the potential construction of the FCC via a dedicated feasibility study that has just delivered a mid-term report – a summary of which was presented at Chamonix. The initiative is accompanied by R&D on key accelerator technologies. The physics case for FCC-ee was well made for an audience of mostly non-particle physicists, concluding that the FCC is the only proposed collider that covers each key area in the field – electroweak, QCD, flavour, Higgs and searches for phenomena beyond the Standard Model – in paradigm-shifting depth.

Environmental consciousness

Sustainability was another focus of the Chamonix workshop. Building and operating future facilities with environmental consciousness is a top priority, and full life-cycle analyses will be performed for any options to help ensure a low-carbon future.

Interesting times, lots to do. To quote former CERN Director-General Herwig Schopper from 1983: “It is therefore clear that, for some time to come, there will be interesting work to do and I doubt whether accelerator experts will find themselves without a job.”

The post Building on success, planning for the future appeared first on CERN Courier.

The key is to reduce the wavelength of the radiation powering the structure down to the optical scale of lasers. By combining solid-state lasers and modern nanofabrication, accelerating structures can be as small as a single micron wide. Though miniaturisation will never allow bunch charges as large as in today’s science accelerators, field strengths can be much higher before structure damage sets in. The trick is to replace highly conductive structures with dielectrics like silicon, fused silica and diamond, which have a much higher damage threshold at optical wavelengths. The length of accelerators can thereby be reduced by orders of magnitude, with millions to billions of particle pulses accelerated per second, depending on the repetition rate of the laser.

Recent progress with “on chip” accelerators promises powerful, high-energy and high-repetition-rate particle sources that are accessible to academic laboratories. Applications may range from localised particle or X-ray irradiation in medical facilities to quantum communication and computation using ultrasmall bunches of electrons as qubits.

Laser focused

The inspiration for on-chip accelerators dates back to 1962, when Koichi Shimoda of the University of Tokyo proposed using early lasers – then called optical masers – as a way to accelerate charged particles. The first experiments were conducted by shining light onto an open metal grating, generating an optical surface mode that could accelerate electrons passing above the surface. This technique was proposed by Yasutugu Takeda and Isao Matsui in 1968 and experimentally demonstrated by Koichi Mizuno in 1987 using terahertz radiation. In the 1980s, accelerator physicist Robert Palmer of Brookhaven National Laboratory proposed using rows of free-standing pillars of subwavelength separation illuminated by a laser – an idea that has propagated to modern devices.

In the 1990s, the groups of John Rosenzweig and Claudio Pellegrini at UCLA and Robert Byer at Stanford began to use dielectric materials, which offer low power absorption at optical frequencies. For femtosecond laser pulses, a simple dielectric such as silica glass can withstand optical field strengths exceeding 10 GV/m. It became clear that combining lasers with on-chip fabrication using dielectric materials could subject particles to accelerating forces 10 to 100 times higher than in conventional accelerators.

In the intervening decades, the dream of realising a laser-driven micro-accelerator has been enabled by major technological advances in the silicon-microchip industry and solid-state lasers. These industrial technologies have paved the way to fabricate and test particle accelerators made from silicon and other dielectric materials driven by ultrashort pulses of laser light. The dielectric laser accelerator (DLA) has been born.

Accelerator on a chip

Colloquially called an accelerator on a chip, a DLA is a miniature microwave accelerator reinvented at the micron scale using the methods of optical photonics rather
than microwave engineering. In both cases, the wavelength of the driving field determines the typical transverse structure dimensions: centimetres for today’s microwave accelerators, but between one and 10 μm for optically powered devices.

Other laser-based approaches to miniaturisation are available. In plasma-wakefield accelerators, particles gain energy from electromagnetic fields excited in an ionised gas by a high-power drive laser (CERN Courier May/June 2024 p25). But the details are starkly different. DLAs are powered by lasers with thousands to millions of times lower peak energy. They operate with more than a million times lower electron charges, but at millions of pulses per second. And unlike plasma accelerators, but similarly to their microwave counterparts, DLAs use a solid material structure with a vacuum channel in which an electromagnetic mode continuously imparts energy to the accelerated particles.

This mode can be created by a single laser pulse perpendicular to the electron trajectory, two pulses from opposite sides, or a single pulse directed downwards into the plane of the chip. The latter two options offer better field symmetry.

As the laser impinges on the structure, its electrons experience an electromagnetic force that oscillates at the laser frequency. Particles that are correctly matched in phase and velocity experience a forward accelerating force (see “Continuous acceleration” image). Just as the imparted force begins to change sign, the particles enter the next accelerating cycle, leading to continuous energy gain.

In 2013, two early experiments attracted international attention by demonstrating the acceleration of electrons using structured dielectric devices. Peter Hommelhoff’s group in Germany accelerated 28 keV electrons inside a modified electron microscope using a single-sided glass grating (see “Evolution” image, left panel). In parallel, at SLAC, the groups of Robert Byer and Joel England accelerated relativistic 60 MeV electrons using a dual-sided grating structure, achieving an acceleration gradient of 310 MeV/m and 120 keV of energy gain (see “Evolution” image, middle panel).

Teaming up

Encouraged by the experimental demonstration of accelerating gradients of hundreds of MeV/m, and the power efficiency and compactness of modern solid-state fibre lasers, in 2015 the Gordon and Betty Moore Foundation funded an international collaboration of six universities, three government laboratories and two industry partners to form the Accelerator on a Chip International Program (ACHIP). The central goal is to demonstrate a compact tabletop accelerator based on DLA technology. ACHIP has since developed “shoebox” accelerators on both sides of the Atlantic and used them to demonstrate nanophotonics-based particle control, staging, bunching, focusing and full on-chip electron acceleration by laser-driven microchip devices.

Silicon’s compatibility with established nanofabrication processes makes it convenient, but reaching gradients of GeV/m requires materials with higher damage thresholds such as fused silica or diamond. In 2018, ACHIP research at UCLA accelerated electrons from a conventional microwave linac in a dual-sided fused silica structure powered by ultrashort (45 fs) pulses of 800 nm wavelength laser light. The result was an average energy gain of 850 MeV/m and accelerating fields up to 1.8 GV/m – more than double the prior world best in a DLA, and still a world record.

Since DLA structures are non-resonant, the interaction time and energy gain of the particles is limited by the duration of the laser pulse. However, by tilting the laser’s pulse front, the interaction time can be arbitrarily increased. In a separate experiment at UCLA, using a laser pulse tilted by 45˚, the interaction distance was increased to more than 700 µm – or 877 structure periods – with an energy gain of 0.315 MeV. The UCLA group has further extended this approach using a spatial light modulator to “imprint” the phase information onto the laser pulse, achieving more than 3 mm of interaction at 800 nm, or 3761 structure periods.

Under ACHIP, the structure design has evolved in several directions, from single-sided and double-sided gratings etched onto substrates to more recent designs with colonnades of free-standing silicon pillars forming the sides of the accelerating channel, as originally proposed by Robert Palmer some 30 years earlier. At present, these dual-pillar structures (see “Evolution” image, right panel) have proven to be the optimal trade-off between cleanroom fabrication complexity and experimental technicalities. However, due to the lower damage threshold of silicon as compared with fused silica, researchers have yet to demonstrate gradients above 350 MeV/m in silicon-based devices.

With the dual-pillar colonnade chosen as the fundamental nanophotonic building block, research has turned to making DLAs into viable accelerators with much longer acceleration lengths. To achieve this, we need to be able to control the beam and manipulate it in space and time, or electrons quickly diverge inside the narrow acceleration channel and are lost on impact with the accelerating structure. The ACHIP collaboration has made substantial progress here in recent years.

Focusing on nanophotonics

In conventional accelerators, quadrupole magnets focus electron beams in a near perfect analogy to how concave and convex lens arrays transport beams of light in optics. In laser-driven nanostructures it is necessary to harness the intrinsic focusing forces that are already present in the accelerating field itself.

On-chip accelerators promise powerful, high-energy and high-repetition-rate particle sources that are accessible to academic laboratories

In 2021, the Hommelhoff group guided an electron pulse through a 200 nm-wide and 80 µm-long structure based on a theoretical lattice designed by ACHIP colleagues at TU Darmstadt three years earlier. The lattice’s alternating-phase focusing (APF) periodically exchanges an electron bunch’s phase-space volume between the transverse dimension across the narrow width of the accelerating channel and the longitudinal dimension along the propagation direction of the electron pulse. In principle this technique could allow electrons to be guided through arbitrarily long structures.

Guiding is achieved by adding gaps between repeating sets of dual-pillar building-blocks (see “Beam control” image). Combined guiding and acceleration has been demonstrated within the past year. To achieve this, we select a design gradient and optimise the position of each pillar pair relative to the expected electron energy at that position in the structure. Initial electron energies are up to 30 keV in the Hommelhoff group, supplied by electron microscopes, and from 60 to 90 keV in the Byer group, using laser-assisted field emission from silicon nanotips. When accelerated, the electrons’ velocities change dramatically from 0.3 to 0.7 times the speed of light or higher, requiring the periodicity of the structure to change by tens of nanometres to match the velocity of the accelerating wave to the speed of the particles.

Although focusing in the narrow dimension of the channel is the most critical requirement, an extension of this method to focus beams in the transverse vertical dimension out of plane of the chip has been proposed, which varies the geometry of the pillars along the out-of-plane dimension. Without it, the natural divergence of the beam in the vertical direction eventually becomes dominant. This approach is awaiting experimental realisation.

Acceleration gradients can be improved by optimising material choice, pillar dimensions, peak optical field strength and the duration of the laser pulses. In recent demonstrations, both the Byer and Hommelhoff groups have kept pillar dimensions constant to ease difficulties in uniformly etching the structures during nanofabrication. The complete structure is then a series of APF cells with tapered cell lengths and tapered dual-pillar periodicity. The combination of tapers accommodates both the changing size of the electron beam and the phase matching required due to the increasing electron energy.

In these proof-of-principle experiments, the Hommelhoff group has designed a nanophotonic dielectric laser accelerator for an injection energy of 28.4 keV and an average acceleration gradient of at least 22.7 MeV/m, demonstrating a 43% energy increase over a 500 µm-long structure. The Byer group recently demonstrated the acceleration of a 96 keV beam at average gradients of 35 to 50 MeV/m, reaching a 25% energy increase over 708 µm. The APF periods were in the range of tens of microns and were tapered along with the energy-gain design curve. The beams were not bunched, and by design only 4% of the electrons were captured and accelerated.

One final experimental point has important implications for the future use of DLAs as compact tabletop tools for ultrafast science. Upon interaction with the DLA, electron pulses have been observed to form trains of evenly spaced sub-wavelength attosecond-scale bunches. This effect was shown experimentally by both groups in 2019, with electron bunches measured down to 270 attoseconds, or roughly 4% of the optical cycle.

From demonstration to application

To date, researchers have demonstrated high gradient (GeV/m) acceleration, compatible nanotip electron sources, laser-driven focusing, interaction lengths up to several millimetres, the staging of multiple structures, and attosecond-level control and manipulation of electrons in nanophotonic accelerators. The most recent experiments combine these techniques, allowing the capture of an accelerated electron bunch with net acceleration and precise control of electron dynamics for the first time.

These milestone experiments demonstrate the viability of the nanophotonic dielectric electron accelerator as a scalable technology that can be extended to arbitrarily long structures and ever higher energy gains. But for most applications, beam currents need to increase.

A compelling idea proposes to “copy and paste” the accelerator design in the cleanroom and make a series of parallel accelerating channels on one chip. Another option is to increase the repetition rate of the driving laser by orders of magnitude to produce more electron pulses per second. Optimising the electron sources used by DLAs would also allow for more electrons per pulse, and parallel arrays of emitters on multi-channel devices promise tremendous advantages. Eventually, active nanophotonics can be employed to integrate the laser and electron sources on a single chip.

Once laser and electron sources are combined, we expect on-chip accelerators to become ubiquitous devices with wide-ranging and unexpected applications, much like the laser itself. Future applications will range from medical treatment tools to electron probes for ultrafast science. According to the International Atomic Energy Agency
statistics, 13% of major accelerator facilities around the world power light sources. On-chip accelerators may follow a similar path.

Illuminating concepts

A concept has been proposed for a dielectric laser-driven undulator (DLU) which uses laser light to generate deflecting forces that wiggle the electrons so that they emit coherent light. Combining a DLA and a DLU could take advantage of the unique time structure of DLA electrons to produce ultrafast pulses of coherent radiation (see “Compact light source” image). Such compact new light sources – small enough to be accessible to individual universities – could generate extremely short flashes of light in ultraviolet or even X-ray wavelength ranges, enabling tabletop instruments for the study of material dynamics on ultrafast time scales. Pulse trains of attosecond electron bunches generated by a DLA could provide excellent probes of transient molecular electronic structure.

The generation of intriguing quantum states of light might also be possible with nanophotonic devices

The generation of intriguing quantum states of light might also be possible with nanophotonic devices. This quantum light results from shaping electron wavepackets inside the accelerator and making them radiate, perhaps even leading to on-chip quantum-communication light sources.

In the realm of medicine, an ultracompact self-contained multi-MeV electron source based on integrated photonic particle accelerators could enable minimally invasive cancer treatments with improved dose control.

One day, instruments relying on high-energy electrons produced by DLA technology may bring the science of large facilities into academic-scale laboratories, making novel science endeavours accessible to researchers across various disciplines and minimally invasive medical treatments available to those in need. These visionary applications may take decades to be fully realised, but we should expect developments to continue to be rapid. The biggest challenges will be increasing beam power and transporting beams across greater energy gains. These need to be addressed to reach the stringent beam quality and machine requirements of longer term and higher energy applications.

The post Acceleration, but not as we know it appeared first on CERN Courier.

Manjit Fifty to 60% of cancer patients can benefit from radiation therapy for cure or palliation. Pain relief is also critical in low- and middle-income countries (LMICs) because by the time tumours are discovered it is often too late to cure them. Radiation therapy typically accounts for 10% of the cost of cancer treatment, but more than half of the cure, so it’s relatively inexpensive compared to chemotherapy, surgery or immunotherapy. Radiation therapy will be tremendously important for the foreseeable future.

What is the state of the art?

Manjit The most precise thing we have at the moment is hadron therapy with carbon ions, because the Bragg peak is very sharp. But there are only 14 facilities in the whole world. It’s also hugely expensive, with each machine costing around $150 million (M). Proton therapy is also attractive, with each proton delivering about a third of the radiobiological effect of a carbon ion. The first proton patient was treated at Berkeley in September 1954, in the same month CERN was founded. Seventy years later, we have about 130 machines and we’ve treated 350,000 patients. But the reality is that we have to make the machines more affordable and more widely available. Particle therapy with protons and hadrons probably accounts for less than 1% of radiation-therapy treatments whereas roughly 90 to 95% of patients are treated using electron linacs. These machines are much less expensive, costing between $1M and $5M, depending on the model and how good you are at negotiating.

Most radiation therapy in the developing world is delivered by cobalt-60 machines. How do they work?

Manjit A cobalt-60 machine treats patients using a radioactive source. Cobalt has a half-life of just over five years, so patients have to be treated longer and longer to be given the same dose as the cobalt-60 gets older, which is a hardship for them, and slows the number of patients who can be treated. Linacs are superior because you can take advantage of advanced treatment options that target the tumour using focusing, multi-beams and imaging. You come in from different directions and energies, and you can paint the tumour with precision. To the best extent possible, you can avoid damaging healthy tissue. And the other thing about linacs is that once you turn it off there’s no radiation anymore, whereas cobalt machines present a security risk. One reason we’ve got funding from the US Department of Energy (DOE) is because our work supports their goal of reducing global reliance on high-activity radioactive sources through the promotion of non-radioisotopic technologies. The problem was highlighted by the ART (access to radiotherapy technologies) study I led for International Cancer Expert Corps (ICEC) on the state of radiation therapy in former Soviet Union countries. There, the legacy has always been cobalt. Only three of the 11 countries we studied have had the resources and knowledge to be able to go totally to linacs. Most still have more than 50% cobalt radiation therapy.

The kick-off meeting for STELLA took place at CERN from 29 to 30 May. How will the project work?

Manjit STELLA stands for Smart Technology to Extend Lives with Linear Accelerators. We are an international collaboration working to increase access to radiation therapy in LMICs, and in rural regions in high-income countries. We’re working to develop a linac that is less expensive, more robust and, in time, less costly to operate, service and maintain than currently available options.

Steinar $1.75M funding from the DOE has launched an 18 month “pre-design” study. ICEC and CERN will collaborate with the universities of Oxford, Cambridge and Lancaster, and a network of 28 LMICs who advise and guide us, providing vital input on their needs. We’re not going to build a radiation-therapy machine, but we will specify it to such a level that we can have informed discussions with industry partners, foundations, NGOs and governments who are interested in investing in developing lower cost and more robust solutions. The next steps, including prototype construction, will require a lot more funding.

What motivates the project?

Steinar The basic problem is that access to radiation therapy in LMICs is embarrassingly limited. Most technical developments are directed towards high-income countries, ultimately profiting the rich people in the world – in other words, ourselves. At present, only 10% of patients in LMICs have access to radiation therapy.

We’re working to develop a linac that is less expensive, more robust and less costly to operate, service and maintain than currently available options

Manjit The basic design of the linac hasn’t changed much in 70 years. Despite that, prices are going up, and the cost of service contracts and software upgrades is very high. Currently, we have around 420 machines in Africa, many of which are down for long intervals, which often impacts treatment outcomes. Often, a hospital can buy the linac but they can’t afford the service contract or repairs, or they don’t have staff with the skills to maintain them. I was born in a small village with no gas, electricity or water. I wasn’t supposed to go to school because girls didn’t. I was fortunate to have got an education that enabled me to have a better life with access to the healthcare treatments that I need. I look at this question from the perspective of how we can make radiation therapy available around the world in places such as where I’m originally from.

What’s your vision for the STELLA machine?

Steinar We want to get rid of the cobalt machines because they are not as effective as linacs for cancer treatment and they are a security risk. Hadron-therapy machines are more costly, but they are more precise, so we need to make them more affordable in the future. As Manjit said, globally 90 or 95% of radiation treatments are given by an electron linac, most often running at 6 MeV. In a modern radiation therapy facility today, such linacs are not developing so fast. Our challenge is to make them more reliable and serviceable. We want to develop a workhorse radiation therapy system that can do high-quality treatment. The other, perhaps more important, key parts are imaging and software. CERN has valuable experience here because we build and integrate a lot of detector systems including readout and data-analysis. From a certain perspective, STELLA will be an advanced detector system with an integrated linac.

Are any technical challenges common to both STELLA and to projects in fundamental physics?

Steinar The early and remote prediction of faults is one. This area is developing rapidly, and it would be very interesting for us to deploy this on a number of accelerators. On the detector and sensor side, we would like to make STELLA easily upgradeable, and some of these upgrades could be very much linked to what we want to do for our future detectors. This can increase the industrial base for developing these types of detectors as the medical market is very large. Software can also be interesting, for example for distributed monitoring and learning.

Where are the biggest challenges in bringing STELLA to market?

Steinar We must make medical linacs open in terms of hardware. Hospitals with local experts must be able to improve and repair the system. It must have a long lifetime. It needs to be upgradeable, particularly with regard to imaging, because detector R&D and imaging software are moving quickly. We want it to be open in terms of software, so that we can monitor the performance of the system, predict faults, and do treatment planning off site using artificial intelligence. Our biggest contribution will be to write a specification for a system where we “enforce” this type of open hardware and open software. Everything we do in our field relies on that open approach, which allows us to integrate the expertise of the community. That’s something we’re good at at CERN and in our community. A challenge for STELLA is to build in openness while ensuring that the machines can remain medically qualified and operational at all times.

How will STELLA disrupt the model of expensive service contracts and lower the cost of linacs?

Steinar This is quite a complex area, and we don’t know the solution yet. We need to develop a radically different service model so that developing countries can afford to maintain their machines. Deployment might also need a different approach. One of the work packages of this project is to look at different models and bring in expertise on new ideas. The challenges are not unique to radiation therapy. In the next 18 months we’ll get input from people who’ve done similar things.

Manjit Gavi, the global alliance for vaccines, was set up 24 years ago to save millions of children who died every year from vaccine-preventable diseases such as measles, TB, tetanus and rubella using vaccinations that were not available to millions of children in poorer parts of the world, especially Africa. Before, people were dying of these diseases, but now they get a vaccination and live. Vaccines and radiation therapy are totally different technologies, but we may need to think that way to really make a critical difference.

Steinar There are differences with respect to vaccine development. A vaccine is relatively cheap, whereas a linac costs millions of dollars. The diseases addressed by vaccines affect a lot of children, more so than cancer, so the patients have a different demographic. But nonetheless, the fact is that there was a group of countries and organisations who took this on as a challenge, and we can learn from their experiences.

Manjit We would like to work with the UN on their efforts to get rid of the disparities and focus on making radiation therapy available to the 70% of the world that doesn’t have access. To accomplish that, we need global buy-in, especially from the countries who are really suffering, and we need governmental, private and philanthropic support to do so.

What’s your message to policymakers reading this who say that they don’t have the resources to increase global access to radiation therapy?

Steinar Our message is that this is a solvable problem. The world needs roughly 5000 machines at $5M or less each. On a global scale this is absolutely solvable. We have to find a way to spread out the technology and make it available for the whole world. The problem is very concrete. And the solution is clear from a technical standpoint.

Manjit The International Atomic Energy Agency (IAEA) have said that the world needs one of these machines for every 200 to 250 thousand people. Globally, we have a population of 8 billion. This is therefore a huge opportunity for businesses and a huge opportunity for governments to improve the productivity of their workforces. If patients are sick they are not productive. Particularly in developing countries, patients are often of a working economic age. If you don’t have good machines and early treatment options for these people, not only are they not producing, but they’re going to have to be taken care of. That’s an economic burden on the health service and there is a knock-on effect on agriculture, food, the economy and the welfare of children. One example is cervical cancer. Nine out of 10 deaths from cervical cancer are in developing countries. For every 100 women affected, 20 to 30 children die because they don’t have family support.

How can you make STELLA attractive to investors?

Steinar Our goal is to be able to discuss the project with potential investor partners – and not only in industry but also governments and NGOs, because the next natural step will be to actually build a prototype. Ultimately, this has to be done by industry partners. We likely cannot rely on them to completely fund this out of their own pockets, because it’s a high-risk project from a business point of view. So we need to develop a good business model and find government and private partners who are willing to invest. The dream is to go into a five-year project after that.

We need to develop a good business model and find government and private partners who are willing to invest

Manjit It’s important to remember that this opportunity is not only linked to low-income countries. One in two UK citizens will get cancer in their lifetime, but according to a study that came out in February, only 25 to 28% of UK citizens have adequate access to radiation therapy. This is also an opportunity for young people to join an industrial system that could actually solve this problem. Radiation therapy is one of the most multidisciplinary fields there is, all the way from accelerators to radio-oncology and everything in between. The young generation is altruistic. This will capture their spirit and imagination.

Can STELLA help close the radiation-therapy gap?

Manjit When the IAEA first visualised radiation-therapy inequalities in 2012, it raised awareness, but it didn’t move the needle. That’s because it’s not enough to just train people. We also need more affordable and robust machines. If in 10 or 20 years people start getting treatment because they are sick, not because they’re dying, that would be a major achievement. We need to give people hope that they can recover from cancer.

The post How to democratise radiation therapy appeared first on CERN Courier.

The cooling method is ingenious – and completely different to ionisation cooling, where muons are focused in absorbers to reduce their transverse momentum. Instead, µ⁺ are slowed to 0.002% of the speed of light in a thin silica-aerogel target, capturing atomic electrons to form muonium, an atom-like compound of an antimatter muon and an electron. Experimenters then ionise the muonium using a laser to create a near monochromatic beam that is reaccelerated in radiofrequency (RF) cavities. The work builds on the acceleration of negative muonium ions – an antimatter muon bonded to two electrons – which the team demonstrated in 2017 (CERN Courier July/August 2018 p8).

Though the analysis is still to be finalised, with results due to be published soon, the cooling and acceleration effect is unmistakable. In accelerator physics, cooling is traditionally quantified by a reduction in beam emittance – an otherwise conserved quantity that reflects the volume occupied by the beam in the abstract space of orthogonal displacements and momenta. Estimates indicate a beam cooling effect of more than an order of magnitude, with the beam then accelerated from 25 meV to 100 keV. The main challenge is transmission. At present one antimatter muon emerges from the RF for every 10 million, which impact the aerogel. Muon decay is also a challenge given that the muonium is nearly stationary in the laboratory frame, with time dilation barely extending the muon’s 2.2 μs lifetime. Roughly a third of the µ⁺ decay before exiting the J-PARC apparatus.

The first application of this technology will be the muon g-2/EDM experiment at J-PARC, where data taking is due to start in 2028. The experiment will add valuable data points to measurements thought to have exceptional sensitivity to new physics (CERN Courier May/June 2021 p25). In the case of the anomalous magnetic moment (g-2) of the muon, theoretical showdowns later this year may either dissipate or reinforce intriguing hints of beyond-the-Standard-Model physics from the Muon g-2 experiment at Fermilab, potentially adding strong motivation to an independent test.

We are very impressed with the progress of our colleagues at J-PARC and congratulate them on their success

“Although our current focus is the muon g-2/EDM experiment, we are open to any possible applications of this technology in the future,” says spokesperson Tsutomu Mibe of KEK. “We are communicating with experts to understand if our technology is of any use in a muon collider, but note that our method cannot be adapted for negative muons.”

While proposals for a µ⁺µ⁺ or µ⁺e^– collider exist, a µ⁺µ^– collider remains the most strongly motivated machine. “Much of the physics interest in e⁺e^– and µ⁺µ^– colliders comes from the annihilations of the initial particles into a photon and/or a Z boson, or a Higgs boson in the case of µ⁺µ^–,” says John Ellis of CERN/KCL. “These possibilities are absent for a µ⁺e^– or µ⁺µ⁺ collider, making them less interesting in my opinion.” From an accelerator-physics perspective, it remains to be demonstrated that the technique can deliver the beam intensity needed for an energy-frontier collider – not least while keeping the emittance low.

“We are very impressed with the progress of our colleagues at J-PARC and congratulate them on their success, says International Muon Collider study leader Daniel Schulte of CERN. “This will profit the development of muon-beam technology and use. We are in contact to understand how we can collaborate.”

The post Muons cooled and accelerated in Japan appeared first on CERN Courier.

The study of the Higgs boson remains central to the LHC programme. ATLAS reported a new result on Standard Model (SM) Higgs-boson production with decays to tau leptons, achieving the most precise single-channel measurement of the vector-boson-fusion production mode to date. Determining the production modes of the Higgs boson precisely may shed light on the existence of new physics that would be observed as deviations from the SM predictions.

Beyond single Higgs production, the di-Higgs production (HH) search is one of the most exciting and fundamental topics for LHC physics in the coming years as it directly probes the Higgs potential (see “Homing in on the Higgs self-interaction“). ATLAS has combined results for HH production in multiple final states, providing the best-expected sensitivity to the HH production cross-section and Higgs-boson self-coupling, allowing κ_λ (the Higgs self-coupling with respect to the SM value) to be within the range –1.2 < κ_λ < 7.2.

The search for beyond-the-SM (BSM) physics to explain the many unresolved questions about our universe is being conducted with innovative ideas and methods. CMS has presented new searches involving signatures with two tau leptons, examining the hypotheses of an excited tau lepton and a heavy neutral spin-1 gauge boson (Z′) produced via Drell-Yan and, for the first time, via vector boson fusion. These results set stringent constraints on BSM models with enhanced couplings to third-generation fermions.

Other new-physics theoretical models propose additional BSM Higgs bosons. ATLAS presented a search for such particles being produced in association with top quarks, setting limits on their cross-section that significantly improve upon previous ATLAS  results. Additional BSM Higgs bosons could explain puzzles such as dark matter, neutrino oscillations and the observed matter–antimatter asymmetry in the universe.

The dark side

Some BSM models imply that dark-matter particles could arise as composite mesons or baryons of a new strongly-coupled theory that is an extension of the SM. ATLAS investigated this dark sector through searches for high-multiplicity hadronic final states, providing the first direct collider constraints on this model to complement direct dark-matter-detection experimental results.

CMS have used low-pileup inelastic proton–proton collisions to measure event-shape variables related to the overall distribution of charged particles. These measurements showed the particle distribution to be more isotropic than predicted by theoretical models.

The LHC experiments also presented multiple analyses of proton–lead (p–Pb) and pp collisions, exploring the potential production of quark–gluon plasma (QGP) – a hot and dense phase of deconfined quarks and gluons found in the early universe that is frequently studied in heavy-ion Pb–Pb collisions, among others, at the LHC. Whether it can be created in smaller collision systems is still inconclusive.

ALICE reported a high-precision measurement of the elliptic flow of anti-helium-3 in QGP using the first Run-3 Pb–Pb run. The much larger data sample compared to the previous Run 2 measurement allowed ALICE to distinguish production models for these rarely produced particles for the first time. ALICE also reported the first measurement of an impact-parameter-dependent angular anisotropy in the decay of coherently photo-produced ρ⁰ mesons in ultra-peripheral Pb–Pb collisions. In these collisions, quantum interference effects cause a decay asymmetry that is inversely proportional to the impact parameter.

CMS reported its first measurement of the complete set of optimised CP-averaged observables from the process B⁰ → K^*0μ⁺μ^–. These measurements are significant because they could reveal indirect signs of new physics or subtle effects induced by low-energy strong interactions. By matching the current best experimental precision, CMS contributes to the ongoing investigation of this process.

LHCb presented measurements of the local and non-local contributions across the full invariant-mass spectrum of B^0* → K^*0μ⁺μ^–, tests of lepton flavour universality in semileptonic b decays, and mixing and CP violation in D → Kπ decays.

The future of the field was discussed in a well-attended panel session, which emphasised exploring the full potential of the HL-LHC and engaging younger generations

From a theoretical perspective, progress in precision calculations has exceeded expectations. Many processes are now known to next-to-next-to-leading order or even next-to-next-to-next-to-leading order (N³LO) accuracy. The first parton distribution functions approximating N³LO accuracy have been released and reported at LHCP, and modern parton showers have set new standards in perturbative accuracy.

In addition to these advances, several new ideas and observables are being proposed. Jet substructure, for instance, is becoming a precision science and valuable tool due to its excellent theoretical properties. Effective field theory (EFT) methods are continuously refined and automated, serving as crucial bridges to new theories as many ultraviolet theories share the same EFT operators. Synergies between flavour physics, electroweak effects and high-transverse-momentum processes at colliders are particularly evident within this framework. The use of the LHC as a photon collider showcases the extraordinary versatility of LHC experiments and their synergy with theoretical advancements.

Discovery machine

The HL-LHC upgrade was thoroughly discussed, with several speakers highlighting the importance and uniqueness of its physics programme. This includes fundamental insights into the Higgs potential, vector-boson scattering, and precise measurements of the Higgs boson and other SM parameters. Thanks to the endless efforts by the four collaborations to improve their performances, the LHC already rivals historic lepton colliders for electroweak precision in many channels, despite the cleaner signatures of lepton collisions. The HL-LHC will be capable of providing extraordinarily precise measurements while also serving as a discovery machine for many years to come.

The future of the field was discussed in a well-attended panel session, which emphasised exploring the full potential of the HL-LHC and engaging younger generations. Preserving the unique expertise and knowledge cultivated within the CERN community is imperative. Next year’s LHCP conference will be held at National Taiwan University in Taipei from 5 to 10 June.

The post LHC physicists spill the beans in Boston appeared first on CERN Courier.

Going green

Based on state-of-the-art technology, the portfolio of current and future accelerator-driven RIs in Europe could develop to consume up to 1% of Germany’s annual electricity demand. With the ambition to maintain the attractiveness and competitiveness of European RIs, and enable Europe’s Green Deal, the Innovate for Sustainable Accelerating Systems (iSAS) project has been approved by Horizon Europe. Its aim is to establish an enhanced collaboration in the field to broaden, expedite and amplify the development and impact of novel energy-saving technologies to accelerate particles.

In general terms, a particle accelerator has a system to create the particles to be accelerated, a system preparing beams with these particles, an accelerating system that effectively accelerates the particle beams, a magnet system to steer the beam, an experimental facility using the particles, and finally a beam dump. In linear accelerating structures, most of the electrical power taken from the grid to operate the accelerator is used by the accelerating system itself.

The core of an accelerating system is a series of cavities that can deliver a high-gradient electric field. For many modern accelerators, these cavities are superconducting and therefore cryogenically cooled to about 2 K. They are powered with radio frequency (RF) power generators to deliver the field at a specific frequency and accordingly to provide energy to the particle beams as they traverse. These superconducting RF (SRF) systems are the enabling technology for frontier accelerators, but are energy-intensive devices where only a fraction of the power extracted from the grid is effectively transmitted to the accelerated particles. In addition, the beam energy is radiated by recirculating beams and ultimately dumped and lost. As an example, the European XFEL’s superconducting RF system uses 5–6 MW for 0.1 MW of average beam power, leading to a power conversion of less than 3%.

The objective of iSAS is to innovate those technologies that have been identified as being a common core of SRF accelerating systems and that have the largest leverage for energy savings with a view to minimising the intrinsic energy consumption in all phases of operation. In the landscape of accelerator-driven RIs, solutions are being developed to reuse the waste heat produced, develop energy-efficient magnets and RF power generators, and operate facilities on opportunistic schedules when energy is available on the grid. The iSAS project has a complementary focus on the energy efficiency of the SRF accelerating technologies themselves. This will contribute to the vital transition to sustain the tremendous 20th-century applications of accelerator technology in an energy-conscious 21st century.

Interconnected technologies

Based on a recently established European R&D roadmap for accelerator technology and based on a collaboration between leading European research institutions and industry, several interconnected technologies will be developed, prototyped and tested, each enabling significant energy savings on their own in accelerating particles. The collection of energy-saving technologies will be developed with a portfolio of forthcoming applications in mind, and to explore energy-saving improvements in accelerator-driven RIs. Considering the developments realised, the new technologies will be coherently integrated into the parametric design of a new accelerating system, a linac SRF cryomodule, optimised to achieve high beam-power in accelerators with an energy consumption that is as low as reasonably possible. This new cryomodule design will enable Europe to develop and build future energy-sustainable accelerators and particle colliders.

iSAS has been approved by Horizon Europe to help develop novel energy-saving technologies to accelerate particles

On 15 and 16 April, the iSAS kick-off meeting was organised at IJCLab (Orsay, France) with around 100 participants. Each of the working groups enthusiastically presented their impactful R&D plans and, in all cases, concrete work has begun. To save energy from RF power systems, novel fast-reacting tuners are being developed to compensate rapidly for detuning of the cavity’s frequency caused by mechanical vibrations, and methods are being invented to integrate them into smart digital control systems. To save energy from the cryogenics, and based on the ongoing Horizon Europe I.FAST project, superconducting cavities with thin films of Nb₃Sn are being further developed to operate with high performance at 4.2 K instead of 2 K, thereby reducing the grid-power to operate the cryogenic system. The cryogenic system requires three times less cooling power to maintain a 4.2 K bath at 4.2 K when heat is dissipated in the bath compared to maintaining a 2 K bath at 2 K. Finally, to save energy from the accelerated particle beam itself, the technology of energy recovery linacs (ERLs) is being improved to operate efficiently with high-current beams by developing novel higher-order mode dampers that significantly avoid heat loads in the cavities.

To address the engineering challenges related to the integration of the new energy-saving technologies, an existing ESS cryovessel will be equipped with new cavities and novel dampers, and the resulting linac SRF cryomodule will be tested in operation in the PERLE accelerator at IJCLab (Orsay, France). PERLE is a growing international collaboration to demonstrate the performance of ERLs with high-power beams that would enable applications in future particle colliders. Its first phase is being implemented at IJCLab with the objective to have initial beams in 2028.

The timescale to innovate, prototype and test new accelerator technologies is inherently long, in some cases longer than the typical duration of R&D projects. It is therefore essential to continue to collaborate and enhance the R&D process so that energy-sustainable technologies can be implemented without delay, to avoid hampering the scientific and industrial progress enabled by accelerators. Accordingly, iSAS plans co-development with industrial partners to jointly achieve a technology readiness level that will be sufficient to enter the large-scale production phase of these new technologies.

Empowering industry

While the readiness of several energy-saving technologies will be prepared towards industrialisation with impact on current RIs, iSAS is also a pathfinder for sustainable future SRF particle accelerators and colliders. Through inter- and multidisciplinary research that delivers and combines various technologies, it is the long-term ambition of iSAS to reduce the energy footprint of SRF accelerators in future RIs by half, and even more when the systems are integrated in ERLs. Accordingly, iSAS will help maintain Europe’s leadership for breakthroughs in fundamental sciences and enable high-energy collider technology to go beyond the current frontiers of energy and intensity in an energy-sustainable way. In parallel, the new sustainable technologies will empower and stimulate European industry to conceive a portfolio of new applications and take a leading role in, for example, the semiconductor, particle therapy, security and environmental sectors.

The post Sustainable accelerator project underway appeared first on CERN Courier.

A first-of-its-kind experiment performed at the European X-Ray Free-Electron Laser (European XFEL) in Hamburg, Germany, has placed new constraints on axion-like particles in a mass range that is relatively unconstrained by laboratory searches. While similar searches have been performed at advanced storage ring-based synchrotron X-ray sources, the new study exploits the higher brightness of the European XFEL’s beams to improve the sensitivity of axion searches in the 10^–3–10⁴ eV mass range.

The axion is predicted to arise from the breaking of Peccei–Quinn symmetry, proposed in the mid-1970s to explain the observed absence of CP violation in strong interactions. Indeed, axion-like particles (ALPs) appear in any quantum field theory with a spontaneously broken global symmetry and arise naturally in many models based on string theory. They are also a promising candidate for dark matter. As such, ALPs are the target of a growing number and variety of experiments worldwide. While not yet able to reach the sensitivity of astrophysical experiments, lab-based searches are less model-dependent as they enable direct control of the axion production process.

Most laboratory searches for axions exploit the Primakoff effect: photons in the presence of a strong external electric field convert into axions, which then convert back into photons after passing through an opaque wall. This “light shining through a wall” technique has been employed in experiments with optical lasers and external magnetic fields, such as ALPS (and now ALPS II) at DESY and OSQAR at CERN. Stringent bounds on heavy axions have also been placed by the CERN Axion Solar Telescope, which looked for the conversion of photons to axions in the strong magnetic field of an LHC dipole magnet pointed at the Sun, and constraints have been set by accelerator experiments such as Belle II at KEK and NA64 at CERN.

The use of X-rays can increase the detection sensitivity by exploiting the strong electric fields (up to 10¹¹ V m^–1, which corresponds to magnetic field strengths of order 1 kT) present in crystalline materials. Gianluca Gregori of the University of Oxford and co-workers used the European XFEL’s HED/HiBEF instrument, in which axion production and photon regeneration are expected to take place via the electric field within a pair of germanium crystals. Orienting the crystals such that their lattice planes are parallel to one another leads to a coherent effect analogous to Bragg scattering, while the much shorter duration and higher brightness of photon pulses from the European XFEL compared to previous synchrotron X-ray experiments allows for a more accurate discrimination of the signal against background.

Using three days of beam time, the team was able to improve on previous lab-based searches at several discrete axion masses. For masses greater than about 200 eV, the team claims to have surpassed the sensitivity of bounds from all previous searches for lab-generated axions except those at NA64. Further improvements in sensitivity – for example by enabling a higher X-ray flux and bunch-number, and by cooling the first crystal to extend the data-acquisition time – are possible, says the team, perhaps bringing the estimated bounds close to the expectation for QCD axions to be dark matter.

“This study shows the power of XFELs, alongside their principal role in more applied domains, to probe fundamental physics mysteries,” says Gregori. “This experiment required a difficult interpretation of a non-standard measurement, and it is hoped that further work will improve on these first limits.”

The post XFELs join hunt for axion-like particles appeared first on CERN Courier.

Plasma wakefield acceleration is a cutting-edge technology that promises to revolutionise the field of particle acceleration by paving the way for smaller and more cost-effective linear accelerators. The technique traces back to a seminal paper published in 1979 by Toshiki Tajima and John Dawson which laid the foundations for subsequent breakthroughs. At its core, the principle involves using a driver to generate wakefields in a plasma, upon which a witness beam surfs to undergo acceleration. Since the publication of the first paper, the field has demonstrated remarkable success in achieving large accelerating gradients.

Traditionally, only laser pulses and electron bunches have been used as drive beams. However, since 2016 the Advanced Wakefield Experiment (AWAKE) at CERN has used proton bunches from the Super Proton Synchrotron (SPS) as drive beams – an innovative approach with profound implications. Thanks to their high stored energy, proton bunches enable AWAKE to accelerate an electron bunch to energies relevant for high-energy physics in a single plasma, circumventing the need for the multiple accelerating stages that are required when using lasers or electron bunches.

Bridging the divide

Relevant to any accelerator concept based on plasma wakefields, AWAKE technology promises to bridge the gap between global developments at small scales and possible future electron–positron colliders. The experiment is therefore an integral component of the European strategy for particle physics’ plasma roadmap, aiming to advance the concept to a level of technological maturity that would allow their application to particle-physics experiments. An international collaboration of approximately 100 people across 22 institutes worldwide, AWAKE has already published more than 90 papers, many in high-impact journals, alongside significant efforts to train the next generation, culminating in the completion of over 28 doctoral theses to date.

In the experiment, a 400 GeV proton bunch from the SPS is sent into a 10 m-long plasma source containing rubidium vapour at a temperature of around 200 °C (see “Rubidium source” figure). A laser pulse accompanies the proton bunch, ionising the vapour and transforming it into a plasma.

To induce the necessary wakefields, the drive bunch length must be of the order of the plasma wavelength, which corresponds to the natural oscillation period of the plasma. However, the length of the SPS proton bunch is around 6 cm, significantly longer than the 1 mm plasma wavelength in AWAKE, and short wavelengths are required to reach large accelerating gradients.

The solution is to take advantage of a beam-plasma instability, which transforms long particle bunches into microbunches with the period of the plasma through a process known as self-modulation. In other words, as the long proton bunch traverses the plasma, it can be coaxed into splitting into a train of shorter “microbunches”. The bunch train resonantly excites the plasma wave, like a pendulum or a child on a swing, being pushed with small kicks at its natural oscillation interval or resonant frequency. If applied at the right time, each kick increases the oscillation amplitude or height of the wave. When the amplitude is sufficiently high, a witness electron bunch from an external source is injected into the plasma wakefields, to ride the wakefields and gain energy.

The first phase of AWAKE (Run 1, from 2016 to 2018) served as a proof-of-concept demonstration of the acceleration scheme. First, it was shown that a plasma can be used as a compact device to self-modulate a highly relativistic and highly energetic proton bunch (see “Self-modulation” figure). Second, it was shown that the resulting bunch train resonantly excites strong wakefields. Third – the most direct demonstration – it was shown that externally injected electrons can be captured, focused and accelerated to GeV energies by the wakefields. The addition of a percent-level positive gradient in density along the plasma led to 20% boosts in the energy gained by the accelerated electrons.

Based on these proof-of-principle experimental results and expertise at CERN and in the collaboration, AWAKE developed a well-defined programme for Run 2, which launched in 2021 following Long Shutdown 2, and which will run for several more years from now. The goal is to achieve electron acceleration with GeV/m energy gain and beam quality similar to a normalised emittance of 10 mm-mrad and a relative energy spread of a few per cent. In parallel, scalable plasma sources are being developed that can be extended up to hundreds of metres in length (see “Helicon plasma source” and “Discharge source” figures). Once these goals are reached, the concepts of AWAKE could be used in particle-physics applications such as using electron beams with energy between 40 and 200 GeV impinging on a fixed target to search for new phenomena related to dark matter.

Controlled instability

The first Run 2 milestone, on track for completion by the end of the year, is to complete the self-modulator – the plasma that transforms the long proton bunch into a train of microbunches. The demonstration has been staged in two experimental phases.

The first phase was completed in 2022. The results prove that wakefields driven by a full proton bunch can have a reproducible and tunable timing. This is not at all a trivial demonstration given that the experiment is based on an instability!

Techniques to tune the instability are similar to those used with free-electron lasers: provide a controlled initial signal for the instability to grow from and operate in the saturated regime, for example. In AWAKE, the self-modulation instability is initiated by the wakefields driven by an electron bunch placed ahead of the proton bunch. The wakefields from the electron bunch imprint themselves on the proton bunch right from the start, leading to a well defined bunch train. This electron bunch is distinct from the witness bunches, which are later accelerated.

The second experimental phase for the completion of the self-modulator is to demonstrate that high-amplitude wakefields can be maintained over long distances. Numerical simulations predict that self-modulation can be optimised by tailoring the plasma’s density profile. For example, introducing a step in the plasma density should lead to higher accelerating fields that can be maintained over long distances. First measurements are very encouraging, with density steps already leading to increased energy gains for externally injected electrons. Work is ongoing to globally optimise the self-modulator.

AWAKE technology promises to bridge the gap between global developments at small scales and possible future electron–positron colliders

The second experimental milestone of Run 2 will be the acceleration of an electron bunch while demonstrating its sustained beam quality. The experimental setup designed to reach this milestone includes two plasmas: a self-modulator that prepares the proton bunch train, and a second “accelerator plasma” into which an external electron bunch is injected (see “Modulation and acceleration” figure). To make space for the installation of the additional equipment, CERN will in 2025 and 2026 dismantle the CNGS (CERN Neutrinos to Gran Sasso) target area that is installed in a 100m-long tunnel cavern downstream from the AWAKE experimental facility.

Accelerate ahead

Two enabling technologies are needed to achieve high-quality electron acceleration. The first is a source and transport line to inject the electron bunch on-axis into the accelerator plasma. A radio-frequency (RF) injector source was chosen because of the maturity of the technology, though the combination of S-band and X-band structures is novel, and forms a compact accelerator with possible medical applications. It is followed by a transport line that preserves the parameters of the 150 MeV 100 pC bunch, and allows for its tight focusing (5 to 10 µm) at the entrance of the accelerator plasma. External injection into plasma-based accelerators is challenging because of the high frequency (about 235 GHz in AWAKE) and thus small structure size (roughly 200 µm) at which they operate. The main goal is to demonstrate that the electron bunch can be accelerated to 4 to 10 GeV, with a relative energy spread of 5 to 8%, and emerge with approximately the same normalised emittance as at the entrance of the plasma (2–30 mm mrad).

For these experiments, rubidium vapour sources will be used for both the self-modulator and accelerator plasmas, as they provide the uniformity, tunability and reproducibility required for the acceleration process. However, the laser-ionisation process of the rubidium vapour does not scale to lengths beyond 20 m. The alternative enabling technology is therefore a plasma source whose length can be scaled to the 50 to 100 metres required for the bunch to reach 50–100 GeV energies. To achieve this, a laboratory to develop discharge and helicon-plasma sources has been set up at CERN (see “Discharge source” figure). Multiple units can in principle be stacked to reach the desired plasma length. The challenge with such sources is to demonstrate that they can produce required plasma parameters other than length.

The third and final experimental milestone for Run 2 will then be to replace the 10 m-long accelerator plasma with a longer source and achieve proportionally larger energy gains. The AWAKE acceleration concept will then essentially be mature to propose particle-physics experiments, for example with bunches of a billion or so 50 GeV electrons.

The post How to surf to high energies appeared first on CERN Courier.

The LHC experiments have surpassed expectations in their ability to squeeze the most out of their large datasets, also demonstrating the wealth of scientific understanding to be gained from improvements to data-acquisition pipelines. Colliding proton bunches at a rate of 40 MHz, the LHC produces a huge quantity of data that must be filtered in real-time to levels that are manageable for offline computing and ensuing physics analysis. When the High-Luminosity LHC (HL-LHC) enters operation from 2029, the data rates and event complexity will further increase significantly.

To meet this challenge, the general-purpose LHC experiments ATLAS and CMS are preparing significant detector upgrades, which include improvements in the online filtering or trigger-selection processes. In view of the importance of this step, the collaborations seek to further enhance their trigger and analysis capabilities, and thus their scientific potential, beyond their currently projected scope.

Following a visit by a group of private donors, in 2023 CERN, in close collaboration with the ATLAS and CMS collaborations, submitted a proposal to the Eric and Wendy Schmidt Fund for Strategic Innovation, which resulted in the award of a $48 million grant. The donation laid the foundations of the Next Generation Triggers project, which kicked off in January 2024. The five-year-long project aims to accelerate novel computing, engineering and scientific ideas for the ATLAS and CMS upgrades, also taking advantage of advanced AI techniques, not only in large-scale data analysis and simulation but also embedded in front-end detector electronics. These include quantum-inspired algorithms to improve simulations, and heterogeneous computing architectures and new strategies to optimise the performance of GPU-accelerated experiment code. The project will also provide insight to detectors and data flows for future projects, such as experiments at the proposed Future Circular Collider, while the associated infrastructure will support the advancement of software and algorithms for simulations that are vital to the HL-LHC and future-collider physics programmes. Through the direct involvement of the CERN experimental physics, information technology and theory departments, it is expected that results from the project will bring benefits across the lab’s scientific programme.

The Next Generation Triggers project is broken down into four work packages: infrastructure, algorithms and theory (to improve machine learning-assisted simulation and data collection, develop common frameworks and tools, and better leverage available and new computing infrastructures and platforms); enhancing the ATLAS trigger and data acquisition (to focus on improved and accelerated filtering and exotic signature detection); rethinking the CMS real-time data processing (to extend the use of heterogeneous computing to the whole online reconstruction and to design a novel AI-powered real-time processing workflow to analyse every collision); and education programmes and outreach to engage the community, industry and academia in the ambitious goals of the project, foster and train computing skills in the next generation of high-energy physicists, and complement existing successful community programmes with multi-disciplinary subjects across physics, computing science and engineering.

“The Next Generation Triggers project builds upon and further enhances the ambitious trigger and data acquisition upgrades of the ATLAS and CMS experiments to unleash the full scientific potential of the HL-LHC,” says ATLAS spokesperson Andreas Hoecker.

“Its work packages also benefit other critical areas of the HL-LHC programme, and the results obtained will be valuable for future particle-physics experiments at the energy frontier,” adds Patricia McBride, CMS spokesperson.

CERN will have sole discretion over the implementation of the Next Generation Triggers scientific programme and how the project is delivered overall. In line with its Open Science Policy, CERN also pledges to release all IP generated as part of the project under appropriate open licences.

The post Next-generation triggers for HL-LHC and beyond appeared first on CERN Courier.

The Electron–Ion Collider (EIC), located at Brookhaven National Laboratory and being built in partnership with Jefferson Lab, has taken a step closer to construction. In April the US Department of Energy (DOE) approved “Critical Decision 3A”, which gives the formal go-ahead to purchase long-lead procurements for the facility.

The EIC will offer the unique ability to collide a beam of polarised high-energy electrons with polarised protons, polarised lightweight ions, or heavy ions. Its aim is to produce 3D snapshots or “nuclear femtography” of the inner structure of nucleons to gain a deeper understanding of how quarks and gluons give rise to properties such as spin and mass (CERN Courier October 2018 p31). The collider, which will make use of infrastructure currently used for the Relativistic Heavy Ion Collider and is costed at between $1.7 and 2.8 billion, is scheduled to enter construction in 2026 and to begin operations in the first half of the next decade.

By passing the latest DOE project milestone, the EIC project partners can now start ordering key components for the accelerator, detector and infrastructure. These include supercon­ducting wires and other materials, cryogenic equipment, the experimental solenoid, lead-tungstate crystals and scintillating fibres for detectors, electrical substations and support buildings. “The EIC project can now move forward with the execution of contracts with industrial partners that will significantly reduce project technical and schedule risk,” said EIC project director Jim Yeck.

More than 1500 physicists from nearly 300 laboratories and institutes worldwide are members of the EIC user group. Earlier this year the DOE and the CNRS signed a statement of interest concerning the contribution of researchers in France, while the UK announced that it will invest £58.8 million to develop the necessary detector and accelerator technologies.

The post EIC steps towards construction appeared first on CERN Courier.

The LHC’s dedicated heavy-ion experiment, ALICE, is to be equipped with an upgraded inner tracking system and a new forward calorimeter to extend its physics reach. The upgrades have been approved for installation during the next long shutdown from 2026 to 2028.

With 10 m² of active silicon and nearly 13 billion pixels, the current ALICE inner tracker, which has been in place since 2021, is the largest pixel detector ever built. It is also the first detector at the LHC to use monolithic active pixel sensors (MAPS) instead of the more traditional hybrid pixels and silicon microstrips. The new inner tracking system, ITS3, uses a novel stitching technology to construct MAPS of 50 µm thickness and up to 26 × 10 cm² in area that can be bent around the beampipe in a truly cylindrical shape. The first layer will be placed just 2 mm from the beampipe and 19 mm from the interaction point, with a much lighter support structure that significantly reduces the material volume and therefore its effect on particle trajectories. Overall, the new system will boost the pointing resolution of the tracks by a factor of two compared to the present ITS detector, strongly enhancing measurements of thermal radiation emitted by the quark–gluon plasma and enabling insights into the interactions of charm and beauty quarks as they propagate through it.

The new forward calorimeter, FoCal, is optimised for photon detection in the forward direction. It consists of a highly granular electromagnetic calorimeter, composed of 18 layers of 1 × 1 cm² silicon-pad sensors paired with tungsten converter plates and two additional layers of 30 × 30 μm² pixels, and a hadronic calorimeter made of copper capillary tubes and scintillating fibres. By measuring inclusive photons and their correlations with neutral mesons, as well as the production of jets and charmonia, FoCal will add new capabilities to explore the small Bjorken-x parton structure of nucleons and nuclei.

Technical design reports for the ITS3 and FoCal projects were endorsed by the relevant CERN review committees in March. The construction phase has now started, with the detectors due to be installed in early 2028 in order to be ready for data taking in 2029. The upgrades, in particular ITS3, are also an important step on the way to ALICE 3 – a major proposed upgrade of ALICE that, if approved, would enter operation in the mid-2030s.

The post New subdetectors to extend ALICE’s reach appeared first on CERN Courier.

These boundary conditions put large-scale science projects under pressure to reduce CO₂ emissions during construction, operation and potentially decommissioning. For context: given the current French energy mix, CERN’s annual 1.3 TWh electricity consumption (which is mostly used for accelerator operation) corresponds to roughly 50 kt CO₂e global warming potential (GWP), while recent estimates for the construction of tunnels for future colliders are in the multi-100 kt CO₂e GWP range.

Green realisation

To discuss potential ways forward, a Workshop on Sustainability for Future Accelerators (WSFA2023) took place on 25–27 September in Morioka, Japan within the framework of the recently started EU project EAJADE (Europe–America–Japan Accelerator Development and Exchange). Around 50 international experts discussed a slew of topics ranging from life-cycle assessments (LCAs) of accelerator technologies with carbon-reduction potential to funding initiatives towards sustainable accelerator R&D, and local initiatives aimed at the “green” realisation of future colliders. With the workshop being held in Japan, the proposed International Linear Collider (ILC) figured prominently as a reference project – attracting considerable attention from local media.

The general context of discussions was set by Beate Heinemann, DESY director for particle physics, on behalf of the European Laboratory Directors Group (LDG). The LDG recently created a working group to assess the sustainability of accelerators, with a mandate to develop guidelines and a minimum set of key indicators pertaining to the methodology and scope of reporting of sustainability aspects for future high-energy physics projects. Since LCAs are becoming the main tool to estimate GWP, a number of project representatives discussed their take on sustainability and steps towards performing LCAs. Starting with the much-cited ARUP study on linear colliders published in 2023 (edms.cern.ch/document/2917948/1), there were presentations on the ESS in Sweden, the ISIS-II neutron and muon source in the UK, the CERN sustainability forum, the Future Circular Collider, the Cool Copper Collider and other proposed colliders. Also discussed were R&D items for sustainable technologies, including CERN’s High Efficiency Klystron Project, the ZEPTO permanent-magnet project, thin film-coated SRF cavities and others.

A second big block in the workshop agenda was devoted to the “greening” of future accelerators and potential local and general construction measures towards achieving this goal. The focus was on Japanese efforts around the ILC, but numerous results can be re-interpreted in a more general way. Presentations were given on the potential of concrete to turn from a massive carbon source into a carbon sink with net negative CO₂e balance (a topic with huge industrial interest), on large-scale wooden construction (e.g. for experimental halls), and on the ILC connection with the agriculture, forestry and fisheries industries to reduce CO₂ emissions and offset them by increasing CO₂ absorption. The focus was on building an energy recycling society by the time the ILC would become operational.

What have we learnt on our way towards sustainable large-scale research infrastructures? First, that time might be our friend: energy mixes will include increasingly larger carbon-free components, making construction projects and operations more eco-friendly. Also, new and more sustainable technologies will be developed that help achieve global climate goals. Second, we as a community must consider the imprint our research leaves on the globe, along with as many indicators as possible. The GWP can be a beginning, but there are many other factors relating, for example, to rare-earth elements, toxicity and acidity. The LCA methodology provides the accelerator community with guidelines for the planning of more sustainable large-scale projects and needs to be further developed – including end-of-life, decommissioning and recycling steps – in an appropriate manner. Last but not least, it is clear that we need to be proactive in anticipating the changes happening in the energy markets and society with respect to sustainability-driven challenges at all levels.

The post Accelerator sustainability in focus appeared first on CERN Courier.

The first part of the workshop was devoted to dark-matter searches and dielectric laser acceleration (DLA). For dark-matter searches, multiple experiments are proposed across different classes (muons vs electrons and positrons, appearance vs disappearance experiments, etc), and an adequate background rejection is important. Promising advanced accelerator technologies are DLA for single electrons – perhaps also muons – and plasma-wakefield accelerators for muons and pions.

Some dark matter-experiments look for an appearance that requires a high flux of incoming particles. For electrons, the standard is set by BDX at JLab, for protons by the proposed SHiP experiment at CERN, and for photons by the proposed Gamma Factory at CERN. In addition, appearances could be seen at existing collider experiments such as the LHC. Other dark-matter experiments search for disappearance. They rely on DC-like electron beams, with prominent examples being LDMX at SLAC and the newly proposed DLA–DMX at PSI. A DC-like muon beam could be explored by the M3 experiment at Fermilab.

Paolo Crivelli (ETH Zürich) described the NA64 experiment as one of the most prominent examples of ongoing accelerator-based dark-matter searches, and presented the first results using a high-energy muon beam. The proposed LDMX experiment at SLAC, presented by Silke Möbius (University of Bern), may set a new standard for indirect dark-matter searches, while advanced concepts employing dielectric laser acceleration, in particular when integrating the accelerating structure with laser oscillator, could achieve many orders of magnitude higher rates of single high-energy electrons entering into an LDMX-type detector.

Uwe Niedermayer (TU Darmstadt), Stefanie Kraus (University Erlangen-Nürnberg) and Raziyeh Dadashi (PSI/EPFL) reviewed the state of the art in DLA plus future plans. Yves Bellouard (EPFL) discussed advances in high-repetition-rate lasers and micro/nano-structures, which suggests that the proposed combined laser-accelerator structures are within reach. Of course, the detector time resolution would also need to be improved tremendously to keep pace with the higher rate of the accelerator.

Acceleration and decay

The second part of the workshop was devoted to the plasma acceleration of non-ultra relativistic and rapidly decaying particles, such as muons and pions. Vladimir Shiltsev (Fermilab) and Daniel Schulte (CERN) presented tentative parameters and ongoing R&D efforts towards a muon collider. Shiltsev also discussed the intriguing possibility of low-emittance muon sources based on plasma-wakefield accelerators, while Alexander Pukhov (Heinrich Heine University Düsseldorf) and Chiara Badiali (IST Lisbon) discussed how plasma acceleration could bring slow particles, such as muons, to relativistic velocities.

The workshop fostered numerous heated discussions and uncovered unresolved issues, which included the “Bern controversy” regarding the ultimate limits of luminosity for PeV energies. Muons are considered particles of choice for future accelerators at the energy frontier. Both low- and high-energy muons have useful applications. Is there an Angstrom limit to the beam diameter? Are tiny beta functions possible? Can plasmas help to overcome such limitations? Understanding and modelling non-point-like particle luminosity is another important topic, also relevant for the Gamma Factory.

The workshop showed how advanced accelerator concepts can jump-start dark-sector searches

The final part of the workshop assembled a roadmap and perspective. DLA studies are to be maintained and, if possible, accelerated. A reasonable target is achieving a gradient of 500 MeV/m and an energy gain of 0.05 GeV in five years on a single wafer, while an integrated DLA laser oscillator could be foreseen five to seven years from now. Plasma-wakefield acceleration of muons could conceivably be tested either at CERN–AWAKE or PSI. It was proposed, as a first step, to put a solid target or tape into the AWAKE set up.

The gamma factory, presented by Witek Krasny (LPNHE), was recognised as an intense source of polarised muons and positrons. For muon-acceleration studies, the dephasing issue, linked to the muons’ non-ultrarelativistic energy, seems to be resolved. A demonstrator experiment for muon plasma acceleration is called for. Open questions include when and where?

Overall, the Bern workshop showed how advanced accelerator concepts can jump start dark-sector searches and muon/pion acceleration. High-repetition-rate acceleration of single electrons for dark-matter searches, using dielectric laser accelerators, and applying high-gradient plasma acceleration to muon and/or pion beams, are intriguing and far-forward looking topics.

The post Pushing accelerator frontiers in Bern appeared first on CERN Courier.

A significant fraction of ICFA’s work is carried out within a set of seven panels, which meet regularly and assemble expertise on more technical or detailed aspects of particular importance to the field. One is devoted to the International Linear Collider (ILC). For more than two decades, ICFA has promoted the realisation of the ILC, for which a global design effort was put in place in 2005. In parallel, an international collaboration under CERN’s leadership had been working on the Compact Linear Collider (CLIC). Recognising the synergies between the two concepts, ICFA established a single coordinating structure, the Linear Collider Collaboration (LCC), in 2012. Also that year, the Japanese high-energy physics community proposed to host the ILC in Japan as a global project.

The LCC mandate came to an end in 2020, when ICFA put in place the ILC International Development Team (IDT) and its working groups. In June 2021 the IDT developed a proposal for the “preparatory laboratory” as a first step towards the realisation of the ILC in Japan.

Evolving landscape

While the IDT is continuing its work, the global Higgs-factory landscape has evolved since the early days of the ILC: more – linear and circular – studies and proposals are on the table, not least as demonstrated by the P5 report in the US. ICFA will soon discuss in what way its discussions and structures need to be adapted to better reflect this evolving landscape.

In November 2023 ICFA established a new panel devoted to the “data lifecycle”, which involves everything from data acquisition, processing, distribution, storage, access, analysis, simulation and preservation, to management, software, workflows, computing and networking. The panel, which replaces two previous ones on related topics, was created in response to the growing importance of data management and open science in recent years. Its membership is currently being put together with the aim to develop ideas and strategies for workforce development and professional recognition mechanisms.

For more than two decades, ICFA has promoted the realisation of the ILC

ICFA’s farthest-reaching and most visible activity is the ICFA Seminar. The 13th ICFA seminar on “Future Perspectives in High-Energy Physics” took place at DESY from 28 November to 1 December 2023. For the first time in six years (the prior ICFA seminar had taken place in 2017 in Ottawa, Canada), this select crowd of scientists, lab directors and funding agency representatives could come together in person for updates and discussions. One highlight was the panel discussion between the directors of KEK, CERN, Fermilab and IHEP, in which views on a future global strategy were discussed. The seminar concluded on a festive note with the formal passing of the ICFA chair baton from Stuart Henderson (JLAB) to Pierluigi Campana (INFN), who will lead ICFA for the next three years.

ICFA is the only global representation of the particle-physics community, and the ideal discussion forum for global strategic developments, especially large international collider projects. In view of the current situation with numerous opportunities for future facilities – not least a future Higgs factory, but also smaller and more diverse projects – the committee and its panels look forward to serving the field of particle physics through continued advocacy, exploration, discussion and facilitation.    

The post A global forum for high-energy physics appeared first on CERN Courier.

The expectations for 2024 are high. For the LHC, the focus is on proton–proton luminosity production, aiming at an unprecedented accumulation of up to 90 fb^–1. This, together with the luminosity forecast for the 2025 run, should provide a sizeable analysis dataset to keep physicists busy during Long Shutdown 3. The 2024 LHC run will conclude with lead–lead collisions, scheduled from 6 to 28 October.

The injector chain also has an ambitious year ahead, serving a busy fixed-target programme. Physics is set to start in the PS East Area on 22 March, followed by the PS n_TOF facility on 25 March. Physics in ISOLDE, downstream of the PS Booster, will start on 8 April, followed by the SPS North Area on 10 April. The antimatter factory is set to start delivering antiprotons to its experiments on 22 April, while the AWAKE facility will run for 10 weeks and the SPS HiRadMat facility for four one-week runs.

Beyond this busy physics programme, many machine development studies and tests are planned in all the machines. One of these tests will take place between mid-March and early June to configure the Linac3 source to produce magnesium ions, which will be accelerated in Linac3, injected into LEIR, and possibly even into the PS. This test will help assess the feasibility and performance of magnesium beams in the accelerator complex, for potential future applications in the LHC and the SPS North Area.

As the countdown to 11 March continues, the operations and expert teams are working diligently to prepare the machines and the beams for another successful physics run.

The post Beams back for a bumper year appeared first on CERN Courier.

CERN has been burrowing beneath the French–Swiss border for half a century. Its first major underground project was the 7 km-circumference Super Proton Synchrotron (SPS), constructed at a depth of around 40 m by a single tunnel boring machine (TBM). This was followed by the Large Electron–Positron (LEP) collider at an average depth of around 100 m, for which the 27 km tunnel was constructed between 1983 and 1989 using three TBMs and a more traditional “drill and blast” method for the sector closest to the Jura mountain range. With a circumference of 90.7 km, weaving through the molasse and limestone beneath Lake Geneva and around Mont Salève, the proposed Future Circular Collider (FCC) would constitute the largest tunnel ever constructed at CERN and be considered a major global civil-engineering project in its own right.

Should the FCC be approved, civil engineering will be the first major on-site activity to take place. The mid-term review of the FCC feasibility study schedules ground-breaking for the first shafts to begin in 2033, after which it would take between six and eight years for each underground sector to be made available for the installation of the technical infrastructure, the machine and the experiments.

Evolving engineering

Since the completion of the FCC conceptual design report in 2018, several significant changes have been made to the civil engineering. These include a 7 km reduction in the overall circumference of the main tunnel, a reduction in the number of surface sites from 12 to eight, and a reduction in the number of permanent shafts from 18 to 12 (two at each of the four experiment sites, one at each of the four technical sites). A temporary shaft will also be required for the construction of the transfer tunnel connecting the injection system to the FCC tunnel, although it may be possible to re-use an existing but unused shaft for this purpose. Additional underground civil engineering for the RF systems will also be required. The diameter of the main tunnel (5.5 m) and its inclination (0.5%) remain unchanged, resulting in a tunnel depth that varies between approximately 50 m – where it passes under the Rhône River – and 500 m – where it passes beneath the Borne plateau on the eastern side of the study site.

The tunnel would be constructed using up to eight TBMs, which are able to excavate and install the tunnel lining in a single-pass operation. Desktop studies show that the geology that would be encountered during most of the underground construction would be favourable, since the molasse rock is usually watertight and can be easily supported using a range of standard rock-support measures. The main beam tunnel will, however, need to pass through about 4.4 km of limestone, which may require the drill-and-blast method to be utilised. These geological assumptions need to be confirmed via a major in situ site investigation campaign planned for 2024–2025.

Two sizes of experiment cavern complexes are envisaged, serving both the lepton and hadron FCC stages. One includes a cavern to house the largest planned FCC-hh detector with dimensions of 35 × 35 × 66 m (similar to the existing ATLAS cavern) and the other a 25 × 25 × 66 m cavern to house the smaller FCC-ee detectors (similar to the CMS cavern). A second cavern 25 m wide and up to 100 m long would be required at each experiment area to house various technical infrastructure, while a 50 m-thick rock pillar between the detector and the service caverns would provide electromagnetic shielding from the detector as well as the overall structural stability of the cavern complex. Numerous smaller caverns and interconnecting tunnels and galleries will be required to link the main structures, and these are expected to be excavated using road-header machines or rock breakers.

Conceptual layouts for two of the eight new surface sites have been prepared under a collaboration agreement with Fermilab, and studies of the experiment site at Ferney-Voltaire in France and the technical site at Choulex/Presinge in Switzerland have been undertaken. The requirements for other surface sites will be developed into preliminary designs in the second half of the feasibility study. In addition, several locations have been investigated for a new high-energy linac, which has been proposed as an alternative to using the SPS as a pre-injector for the FCC, with the most promising site located close to the existing CERN Prévessin site.

Feasibility campaign

As an essential step in demonstrating the feasibility of underground civil-engineering works for the FCC, CERN has been working with international consultants and the University of Geneva to develop a 3D geological model using information gathered from previous borehole and geophysical investigations. To improve this understanding, a targeted campaign of subsurface investigations using a combination of geophysical analyses and deep-borehole drilling has been planned in the areas of highest geological uncertainty. The campaign, which is currently being tendered with specialist companies, will commence in 2024 and continue into 2025 to ensure that the results are available before the end of the feasibility study. About 30 boreholes will be drilled and used in conjunction with 80 km of seismic lines to investigate the location of the molasse rock, in particular under Lake Geneva, the Rhône river and in those areas where limestone formations may be close to the planned tunnel horizon.

On the surface, there is scope for staging the construction of buildings. All the buildings that are only required for the FCC-hh phase would be postponed, but the land areas needed for them would be reserved and included in the overall site perimeter. Buried networks, roads and technical galleries would be designed and constructed such that they can be extended later to accommodate the FCC-hh structures.

With a total of around 15 million tonnes of rock and soil  to be excavated, sustainability is a major focus of the FCC civil-engineering studies. To this end, in the framework of the European Union co-funded FCC Innovation Study, CERN and the University of Leoben launched an international challenge-based competition, “Mining the Future”, in 2021 to identify credible and innovative ways to reuse the molasse. The results of the competition include the use of limestone for concrete production and stabilisation of constructions within the project, the re-use of excavated materials to back-fill quarries and mines, the transformation of sterile molasse into fertile soil for agriculture and forestry, the production of bricks from compressed molasse, and the development of novel construction materials with molasse ingredients for use in the project as far as technically suitable. The next step is the implementation of a pilot “Open Sky Laboratory” permitting the demonstration of the separation techniques of the winning consortium (led by BG engineering), and collaboration with CERN’s host states and other stakeholders to identify suitable locations for its use. In addition, the FCC feasibility study is working towards a full assessment to minimise the carbon footprint during construction.

The civil-engineering plans for the FCC project have been presented several times to the global tunnelling community, most recently at the 2023 World Tunnel Congress in Athens. The scale and technical complexity of the project is creating a great deal of interest from designers and contractors, and has even triggered a dedicated visit to CERN from the executive committee of the International Tunnelling Association, which reinforces the significant progress that has been made.

The post Tunnelling to the future appeared first on CERN Courier.

Vacuum system

The CERN vacuum group has been actively designing components for the FCC-ee vacuum system. Among them are 3D-printed synchrotron-radiation absorbers (SRAs), cold-sprayed copper “bosses”, which could be machined to obtain weld- and flange-free beam position monitor button electrodes (pictured), and plasma-sprayed thin titanium tracks to be used as a radiation-hard bake-out heating system. In parallel, a collaboration with a spin-off company from the University of Calabria is dealing with the implementation of shape-memory alloy flanges. The design of a 2 m-long vacuum chamber extrusion with one SRA is almost finalised, and a soon-to-be-built prototype will be tested at the KARA light source at KIT. We have also begun studying a vacuum chamber with a smaller inner diameter compared to the FCC-ee baseline, including its impact on the machine–detector interface and the booster. The length of the vacuum sectors has been optimised, and their integration in the overall tunnel design is under study. The vacuum group is also looking forward to prototyping the required NEG-coating set-up, as the vacuum chambers could be up to 12 m long and coating them in a vertical position, as is usually done, would be difficult, especially for industry when moving to mass production.

Robert Kersevan CERN.

Superconducting cavities

A key goal of R&D for the FCC superconducting radio-frequency (SRF) system, conducted by the CERN SY–RF, TE–VSC and EN–MME groups, is to optimise Nb/Cu technology for the fabrication of the cavities. Achieving high SRF performance in thin-film-coated cavities requires minimising substrate defects. Previous experiences show that imperfections located around electron beam welds in areas subjected to high magnetic field areas can constrain the quality factor of Nb/Cu cavities. To surpass the current limitations of Nb-coated cavities, a seamless configuration along with higher substrate quality and shape conformity is a promising alternative. Instead of traditional shaping methods such as deep-drawing or spinning, the ongoing use of techniques such as hydroforming and machining directly from the bulk material shows high potential for valuable results without altering the substrate. Moreover, it ensures effectiveness, repeatability and precision in the final shape of the cavity. Based on the impressive RF performance obtained from seamless Nb-coated 1.3 GHz cavities manufactured at CERN from bulk copper, the CERN teams are confident that such spectacular results will be repeated with a 400 MHz cavity (pictured) that is being machined as a preliminary prototype for the FCC RF study.

Said Atieh CERN.

HTS main arc magnets

At the end of 2023, the first demonstrator of a high-temperature superconductor (HTS) sextupole designed for the FCC-ee arcs was fabricated at CERN (pictured). Built using novel technology from a CERN spin-off company, the magnet adopts a “canted cosine theta” design and is the first such device to use HTS rare-earth barium copper oxide (ReBCO) tape as its conductor – something that was long considered technically challenging. The main advantage of such a magnet is that ohmic losses (a significant source of electric power consumption for a normal-conducting accelerator) are reduced to zero, whereas refrigeration losses are much reduced compared to low-temperature-superconductor devices. Other advantages include increased performance due to the possibility of “nesting” magnets together, which is not possible for normal-conducting magnets that use iron to shape their magnetic fields. The increase in performance is such that up to 40% of the cost of the system can be recovered from the lower required RF voltage and therefore a smaller number of accelerating RF cavities. The magnet is the fruit of a CERN–PSI collaboration called FCCee-HTS4, funded through the CHART consortium in Switzerland. Future plans include the winding of the magnet at CERN, followed by tests for magnetic performance and quality.

Mike Koratzinos PSI.

Machine–detector interface alignment

Designed to meet strict alignment requirements in the FCC-ee interaction points, the Machine Detector Interface (MDI) alignment system is a key element of the feasibility study. Challenging conditions – including extremely low temperatures, elevated radiation levels and limited space – hinder the deployment of standard survey equipment and sensors in this important region. New and exotic techniques and sensing systems have therefore been studied. The main solution, called in-lined multiplexed and distributed frequency scanning interferometry (IMD–FSI), uses an interferometer with a wavelength-sweeping laser source to measure multiple lengths along a single optical fibre, simultaneously and independently. A network of fibres can then be installed in a helical pattern to monitor the shape of components inside the MDI, such as the support of the screening solenoid. A prototype IMD–FSI system (pictured) has proved extremely promising, and the next step is a full fibre network implementation on a cylinder. This system could also be implemented in other regions of the collider, for example to monitor sensitive tunnel sections or other civil-engineering structures such as towers, dams and bridges.

Léonard Watrelot CERN.

The post Advancing hardware appeared first on CERN Courier.

Designing a next-generation collider with a performance that meets the scientific demands of the particle-physics community is one thing. Ensuring its territorial compatibility, technical feasibility and cost control is quite another. A core element of the FCC feasibility study is therefore the placement of the ring and the necessary surface sites, for which an iterative approach in collaboration with CERN’s host states, France and Switzerland, has been adopted from the outset.

Territorial compatibility requires numerous natural, technical, urban and cultural constraints to be identified and considered. The goal is to limit the consumption of land, keep the quantity of excavated materials to a minimum and re-use as much as possible, minimise the consumption of resources such as electricity and water, avoid visibility, noise and dust nuisances, and create synergies with future neighbours where possible. Following eight years of intense study, one configuration was identified out of some 100 variants as being particularly suitable. This scenario has a circumference of about 90.7 km, eight surface sites and permits the installation of up to four experiments.

During 2023 this reference scenario was reviewed with different regional stakeholders and now serves as the baseline for further design and optimisation activities. These include geophysical and geotechnical investigations to set the optimum depth of the tunnel, links to high voltage grids, access to water for cooling purposes, connections to major rail and road infrastructures, landscape integration and the development of sustainable mitigation measures.

Drill down

Working out how to place a 90.7 km-circumference research infrastructure in a densely populated region requires several dozens of criteria to be met. While initial investigations concerned observations at the square-kilometre level, the focus gradually moved to thousands of square metres and individual land-plot levels. Initial cartographic and database research has progressively been replaced with analysis in the field, working meetings with public administration services and eventually individuals with expert local knowledge. In addition to the scientific and technical requirements, the FCC implementation scenario takes into account  the project-implementation risks, cost impacts, access to resources (electricity, water, land), transport requirements, and estimates of the urban and demographic evolution. The study also analyses socio-economic benefits for the region.

The reference layout with only eight surface sites requires less than 50 ha of land use on the surface and constitutes a significant reduction in footprint with respect to the initial scenario drawn up in 2014. All sites are situated close to road infrastructure, with less than 5 km of new roads required, and several of the eight sites are located in the vicinity of 400 kV grid lines. The layout of the FCC is integrated geographically with the existing CERN accelerator complex, with beam transfer possible from either the LHC or via the SPS tunnel.

Throughout all studies, CERN has been accompanied by the services of the Swiss and French authorities at different levels

The feasibility study, carried out with relevant consultancy companies, confirms the technical feasibility of all eight surface sites and the underground works. Working meetings with all the municipalities affected in France and Switzerland have not revealed any showstoppers so far, even if decisions by municipalities and the host states are yet to be taken. Next steps include the detailed integration of the surface sites in the environment.

Timescales are critical to be able to continue with such studies. By the end of the feasibility study in 2025, all land plots that are required by the project need to be communicated to the host states. In addition, a formal environmental evaluation phase in both France and Switzerland is necessary for the authorisation procedures. These activities rely on an agreement between CERN and the host states on the steps to be made by each stakeholder, including the associated legal and regulatory conditions.

Throughout all studies, CERN has been accompanied by the services of the Swiss and French authorities at different levels. This dialogue concerns the more detailed expression of the needs and constraints of the local actors and the identification of potential co-development topics and compensatory measures. The findings are gradually being integrated into a process of project optimisation of the reference scenario to further improve its added value for the territory while keeping the science value high and the project implementation risks low.

The post Where and how? appeared first on CERN Courier.

Precise measurements of the Higgs boson’s properties serve as probes into the underlying fundamental physics principles of the SM and beyond. For this reason, in September 2012 Chinese scientists proposed the Circular Electron–Positron Collider (CEPC) and the Super proton–proton Collider (SppC) as an international, large science project hosted in China to match the grand goals of particle physics, complementary to linear and muon colliders. Around the same time, physicists at CERN proposed the Future Circular Collider (FCC) staged across electron-positron (e⁺e^–) and hadron-hadron operations.

Since then, the global high-energy physics community has reached consensus on the importance of an e⁺e^– Higgs factory as the next collider after the LHC. In Europe, the 2020 update of the European strategy for particle physics concluded that a Higgs factory is the highest priority, while the US Snowmass 2021 community study and subsequent P5 report released in December 2023 also stressed the importance of overseas Higgs factories. CEPC scientists have actively contributed to both exercises. Meanwhile in Japan, which proposed to host an International Linear Collider (ILC) Higgs factory in 2012, a new baseline design to start at a collision energy of 250 GeV instead of 500 GeV was presented in 2017.

In China, both the 464th and 572th Xiangshan Science Conferences in 2013 and 2016 concluded that “CEPC is the best approach and a major historical opportunity for the national development of an accelerator-based high-energy physics programme”. In 2023, CEPC was identified as the top future particle accelerator in the planning study conducted by the Chinese Academy of Sciences (CAS). This followed an April 2022 statement by the International Committee for Future Accelerators (ICFA) that “reconfirms the international consensus on the importance of a Higgs Factory as the highest priority for realising the scientific goals of particle physics” and expressed support for Higgs-factory proposals worldwide. Five years after the publication of a conceptual design report in November 2018, a technical design report (TDR) for the CEPC accelerator – numbering more than 1000 pages and representing the first such report for a Higgs factory based on a circular collider – has now been completed.

CEPC is a circular Higgs factory comprising four accelerators: a 30 GeV linac, a 1.1 GeV damping ring, a booster with an energy up to 180 GeV, and a collider operating at four different energy modes corresponding to ZH production (240 GeV), the Z-pole (91 GeV), the W⁺W^– threshold (160 GeV) and the tt threshold (360 GeV). The machines are connected by 10 transport lines. While the linac and damping ring would be constructed on the surface, the booster and collider would be situated in an underground ring with a circumference of 100 km, reserving space for a later hadron collider, SppC.

CEPC in focus

The CEPC collider features a double-ring structure, with electron and positron beams circulating in opposite directions in separate beam pipes and colliding at two interaction points where large detectors will be installed. The 100 km-circumference full-energy CEPC booster, positioned atop the collider in the same tunnel, functions as a synchrotron featuring a 30 GeV injection energy and an extraction energy equal to the beam collision energy. To maintain constant luminosity, top-up injection will be employed. The 1.8 km-long linac, which serves as an injector to the booster, accelerates both electrons and positrons using S- and C-band radio-frequency systems, equipped with a damping ring to reduce positron emittance. As an alternative option, polarisation schemes are also under study.

A follow-up to CEPC is SppC, a proton–proton collider with a centre-of-mass energy of up to 125 TeV. The tunnel, primarily consisting of hard rock that will be excavated using either a tunnel boring machine or drill-and-blast methods, allows the SppC to be installed without removing the CEPC. This unique layout opens exciting long-term possibilities for electron–proton and electron–ion physics in addition to the CEPC’s e⁺e^– and the SppC’s proton–proton and ion–ion physics operations. Furthermore, the CEPC would be configured to operate as a high-energy synchrotron-radiation light source with two gamma-ray beamlines, extending the usable synchrotron-radiation spectrum to unprecedented energy (from 100 keV to more than 100 MeV) and brightness ranges. The 30 GeV injection linac can also produce a high-energy X-ray free electron laser by adding an undulator.

Dedicated goals

The CEPC operation plan and physics goals follow a “10-2-1-5” scheme, dedicating 10 years as a Higgs factory, two years as a Z factory, one year as a W factory and possibly an additional five years’ operation at the tt threshold. The four collision modes (corresponding to H, Z, WW and tt production) have a baseline synchrotron radiation power of 30 MW per beam. Luminosity upgrades are also considered by increasing the synchrotron-radiation power per beam up to 50 MW, reaching a luminosity of 8 × 10³⁴ at 240 GeV. With the upgraded luminosity plan, 4.3 million Higgs bosons, 4.1 trillion Z bosons, 210 million W bosons and 0.6 million tt pairs would be produced in the two CEPC detectors.

After the completion of the CEPC conceptual design report, the accelerator entered a five-year-long TDR study during which the design was further optimised. The resulting report, released on 25 December 2023, emphasises the optimal luminosity, coverage of H, Z, W and tt energies, and the full spectrum of technology R&D, civil-engineering designs, industrial and international collaborations and participation.

Smaller emittances at the interaction points have been adopted to increase the luminosities, dynamic apertures including various errors for four energies match the design goals, beam–beam and collective effects have been verified, and the machine–detector interface has been optimized with a 20 cm-diameter central beryllium pipe at the interaction points. The booster has adopted a theoretical minimum emittance-like lattice design with an injection energy raised to 30 GeV and output energy of up to 180 GeV.

CEPC accelerator R&D has been conducted in synergy with the fourth-generation 6 GeV High Energy Photon Source project at IHEP in Beijing. These R&D activities cover the collider and booster magnets, superconducting quadrupoles for the insertion regions, NEG-coated vacuum chambers, superconducting cryomodules, cryogenic systems, continuous-wavelength high-efficiency klystrons, magnet power supplies, mechanics, S-band and C-band linac and positron source, damping ring, instrumentation and feedbacks, control system, survey and alignment, radiation protection and environmental aspects.

CEPC is the best approach and a major historical opportunity for the national development of an accelerator-based high-energy physics programme

As three examples, firstly the CEPC booster 1.3 GHz 8 × 9-cell cavity cryomodule has been shown to reach a quality factor/accelerating gradient of 3.4 × 10¹⁰/23 MVm^–1, surpassing the booster specification (see “CEPC technologies”, left image). Secondly, the CEPC 650 MHz one-cell cavity reached 2.3 × 10¹⁰/41.6 MVm^–1 at 2 K with electrical-polishing treatment and 6.3 × 10¹⁰/31 MVm^–1 with medium-temperature treatment. Thirdly, three collider-ring 650 MHz, 800 kW continuous-wavelength high-efficiency klystrons have been developed at IHEP, where the second klystron (see “CEPC technologies”, right image) has reached an efficiency of 77.2% at 849 kW in pulsed mode compared with the design value of 77% at 800 kW in CW mode. The third klystron is a multibeam klystron with a design goal of 80.5%, and its electron source is currently undergoing tests. The achievements of the CEPC accelerator TDR are also a result of strong industrial participation and contributions, via the CEPC industrial promotion consortium.

High-energy ambitions    

As part of future strategic technology R&D in high-energy physics and beyond, the CEPC team has proposed an alternative beam-driven plasma injector with beam energies from 10 to 30 GeV. To develop and demonstrate the necessary plasma technologies, such as positron acceleration, staged acceleration and high beam qualities for future linear colliders, IHEP initiated a plasma acceleration experimental programme in September 2023 using the injector linac of BEPCII (a 1.89 GeV e⁺e^– collider with a luminosity of 10³³ cm^–2s^–1) and experimental facilities funded by CAS to the tune of RMB 0.12 billion ($17 million). 

The SppC, in conjunction with the CEPC, would not only provide unprecedented precision on Higgs-boson measurements but explore a significantly larger region of the new-physics landscape, propelling our understanding of the physical world to new heights. A future hadron collider is both more costly than a Higgs factory and more technically challenging. Critical issues such as high-field (20 T or higher) superconducting magnets, synchrotron radiation in a cryogenic environment and a sophisticated beam-collimation system for quench protection must be adequately addressed before construction can begin.

High-field magnets based on high-temperature iron-based superconductors are proposed as the key development path for the SppC. This technology has a much higher magnetic field potential (>30 T) and lower cost than the NbTi/Nb₃Sn technologies used nowadays, and significant progress has been made, together with industry, during the past eight years. In 2016 more than 100 m of iron-based “7-core” tape was fabricated, reaching a current density of 450 A/mm² at 10 T and 4.2 K in 2022.

The SppC is expected to achieve a peak luminosity of 10³⁵ cm^–2s^–1 per interaction point and an integrated luminosity of approximately 30 ab^–1, assuming two interaction points and a runtime of 20–30 years. To further reduce the energy consumption of SppC and CEPC (which has a total power consumption of 262 MW at the ZH energy with a synchrotron-radiation power of 30 MW per beam), various countermeasures are under study.

From 2019 to 2022, CEPC accelerator activities were guided by an International Accelerator Review Committee. In June and September 2023, the CEPC accelerator international TDR and cost review were carried out at Hong Kong University of Science and Technology, while the civil-engineering cost was reviewed by a domestic committee in June 2023. The total CEPC cost is estimated at RMB 36.4 billion ($5.15 billion), with accelerator, infrastructure and experiments taking up RMB 19 billion, 10.1 billion and 4 billion, respectively. Among all the CEPC candidate sites, three – Qinhuangdao, Huzhou and Changsha – have been studied in the TDR.

At the end of October 2023, the CEPC international advisory committee supported the conclusion of the TDR review that the accelerator team is well prepared to enter an engineering design report (EDR) phase. The following month, CEPC–SppC proposals were presented at the ICFA Seminar at DESY, declaring the completion of the CEPC accelerator TDR.

Concerning the technology and status of the CEPC detectors, a full spectrum R&D programme has been carried out, spanning the pixel vertex detector, silicon tracker, time projection chamber and drift chamber, time-of-flight detector, calorimeters, high-temperature superconducting solenoid and mechanical design, among others. This R&D also benefits from past experiences with BESIII (in particular concerning the drift chamber and superconducting magnet) and from the High-Luminosity LHC upgrades for ATLAS and CMS (such as the silicon-strip detector and high-granularity calorimeter). The CEPC detector TDR reference design began in January 2024 and will be completed in mid-2025 within the EDR phase (2024–2027).

EDR and schedule

The aim is to present the CEPC proposal (including accelerator, detector and engineering) for selection by the Chinese government around 2025, with construction to start in around 2027 and to be completed around 2035. A preliminary accelerator EDR plan has been established and is to be reviewed by the International Accelerator Review Committee in 2024.

The SppC, in conjunction with the CEPC, would propel our understanding of the physical world to new heights

Concerning CEPC development towards construction, CAS is planning for China’s 15th “five-year plan” for large science projects, for which a steering committee chaired by the CAS president was established in 2022. High-energy physics and nuclear physics, one of eight fields in the plan, has selected nine proposals that have been reviewed in an open and international way. CEPC is ranked first, with the smallest uncertainties by every committee (including domestic committees and an international advisory committee). A final report has been submitted to CAS for consideration.

CEPC has always been envisioned as an international big-science project, and participation is warmly welcomed both in scientific and industrial ways. The CEPC accelerator TDR represents the efforts of thousands of domestic and overseas scientists and engineers. Such a facility would play an important role in future plans of the worldwide high-energy physics community, deepening our understanding of matter, energy and the universe to an unprecedented degree while facilitating extensive research and collaboration to explore the frontiersof technology.

The post China’s designs for a future circular collider appeared first on CERN Courier.

The physics landscape has changed. We have not seen signs of new particles above the Higgs-boson mass. Typical limits are now well above 1 TeV based on LHC data, which means we need to look for the new physics that we anticipate at higher energies. The consensus during the recent US Snowmass process was that we should aim for 10 TeV in the centre-of-mass. A muon collider has the feature that its expected wall-plug power scales very favourably as you go to the multi-TeV scale. While significant technology development is required to establish the overall feasibility, performance and cost of such a machine, our current performance estimates make it a very interesting candidate. This motivates an active R&D and design programme to validate this approach.

Why was the US Muon Accelerator Program (MAP) discontinued a decade ago?

MAP was approved in early 2011 to assess the feasibility of the technologies required. By 2014, the community had just discovered the Higgs boson and was focused on pursuing a Higgs factory. Mature concepts based on superconducting (ILC) and normal-conducting (CLIC) linear-collider technologies were at hand, and these approaches envisioned subsequent energy upgrades that would enable the exploration of a new-particle spectrum extending into the TeV scale. Because of the relatively low mass of the Higgs, work was also going into a large circular collider design that would represent minimal technical risk. A muon collider, a concept with much lower overall maturity level and with significantly different operating characteristics, did not appear to provide a timely path to realising the Higgs factory.

The other application of interest involving muon–accelerator technologies was the neutrino factory. However, the field concluded that a long-baseline neutrino experiment based on the “superbeam source” represented the best path forward. In a constrained budget environment, the concepts being pursued by MAP didn’t have sufficient priority and support to continue.

What do we know so far about the feasibility of a muon collider?

As the MAP effort concluded, several key R&D and design efforts were nearing completion and were subsequently published. These included demonstrations of normal-conducting RF cavities in multi-Tesla magnetic fields operating with >50 MV/m accelerating gradients, simulated 6D cooling-channel designs capable of achieving the necessary emittance cooling for collider applications, and a measurement of the cooling process at the international Muon Ionization Cooling Experiment (MICE). While MICE only characterised the performance of a partial cooling cell, the precise measurements provided by its tracking detector system confirmed that the muons behaved consistently with the cooling process as described in the simulation codes that were employed to design the cooling channel for a high-brightness muon source.

Any future collider operating at the energy frontier will have to be supported by a global development team

Another key advance was detailed simulations of the performance of a muon-collider detector in the lead-up to the last European strategy update. These efforts, utilising the beam-induced background samples prepared by MAP, demonstrated that useful physics results could be obtained with reasonable assumptions about the performance of the individual elements of the detector.

How are things going with the International Muon Collider Collaboration (IMCC)?

The IMCC, led by CERN with European funding support from the MuCol project, presently coordinates global activities towards R&D and design. The collaboration’s input has been crucial in developing the technically limited timeline towards a multi-TeV muon collider as outlined in the accelerator R&D roadmap commissioned by the European Laboratory Directors Group. The IMCC is making excellent progress towards a reference design for the muon-collider complex as well as defining a cooling demonstrator. An interim report is currently being prepared. However, current funding levels for the effort correspond to roughly half of the estimated levels required to achieve the technically limited timeline. With the strong support for pursuing an energy-frontier muon collider in the US, it is hoped that a fully global effort will be able to support the effort at levels that much more closely match the requirements of a technically limited timeline.

How does the IMCC relate to the P5 recommendations for reinvigorated muon collider R&D at Fermilab?

Any future collider operating at the energy frontier will have to be supported by a global development team, and the issue of where such a machine can be sited will depend on a complex set of circumstances that we certainly can’t predict now. The fundamental goal is to identify the technology and one or more sites where it can be deployed so that we are able to continue our exploration of the fundamental building blocks and processes in the universe for all humankind. Thus, the current IMCC activities are fully aligned with the aspiration expressed by P5 to explore the option for conducting muon collider R&D in the US and exploring the possibility of Fermilab as a host site for a future machine.

What are the key accelerator challenges to be overcome?

While there are a number of challenging subsystems to engineer, the most novel aspect of the machine remains the ionisation cooling channel. Demonstration of the beam operations of a cooling module at high beam intensity will be necessary to give us confidence that the technology is robust enough for high-energy physics applications. In addition to this absolutely unique subsystem of the muon collider, we require detailed end-to-end simulations of the overall machine performance, detailed engineering conceptual designs for all key components, and successful engineering demonstrations of suitable-scale prototypes for several critical systems. These include the target, the fast-ramping magnet system for the high-energy accelerator stages, the large-aperture collider ring magnets that must be adequately shielded against the decay products of the muon beams, and detector subsystems that can robustly operate in an environment with the beam-induced backgrounds from the muon decays.

And the detector challenges?

Tremendous progress in detector technology has resulted from the design and operation of the LHC detectors. Further progress in obtaining precision physics measurements in very high-occupancy environments as we prepare for the HL-LHC provides confidence for the detector requirements of a muon collider, which will have to deal with similar hit rates. While the details of the occupancy in the detectors for these two types of machine are not identical, the concepts being implemented for better time and spatial segmentation appear quite effective for both.

A particular feature of the muon collider detector is the “shielding nozzle” that was first introduced in MAP to protect the innermost detector elements. These nozzles impact the overall physics performance by limiting the near-axis coverage. However, with detailed detector performance studies underway, we are now in a position to carry out detailed detector and shielding studies to optimise these elements for overall physics performance.

How is the vast neutrino flux being addressed?

The very high-energy muon beams in a collider result in a narrow cone of neutrinos being produced in the forward direction as they circulate around the collider ring. When the beams are moving through dipoles, the constant change in transverse direction helps to dilute this flux, but any straight sections in the ring effectively act as a high-energy neutrino source that shines in a specific direction. The tremendous flux of neutrinos from a straight section of a TeV-scale collider are expected to create ionising radiation wherever they exit Earth’s surface. Thus, there are a set of mitigation strategies incorporated into the design effort to make sure that there are absolutely no risks. This includes minimising the number of straight sections, incorporating magnet-movers that allow the vertical trajectories of the beams to be changed slowly throughout the collider, and ensuring that the beams do not exit in populated areas. 

What does the timeline for a 10 TeV muon collider look like?

We need to deliver a complete end-to-end reference design in time for the next European strategy update and for the US interim panel review that was recommended in the P5 report. A conceptual design report (CDR) for a demonstrator facility then has to be completed such that construction could begin by around 2030. Over the course of the next decade, the engineering design concepts for each subsystem have to be prepared and prototyping R&D has to be carried out, while also producing a CDR for the high-energy facility, including detailed performance simulations. By the late 2030s, the demonstrator facility and prototyping programme would enable detailed technical specifications for all key systems. Upgrades to the demonstrator facility could be necessary to further clarify performance and technical specifications. The final steps would be to complete a technical design that incorporates results from the demonstrator programme and to develop site-specific plans for the labs that would like to be considered as potential hosts for the facility. The start of 10 TeV collider operations would then be guided by a physics-driven plan, including potential intermediate stages, but likely at least a decade after construction approval.

The current schedule puts physics operations of a high-energy muon collider about five years earlier than an FCC-ee. Is this realistic?

I would characterise these two timelines as being of different types. The FCC-ee timeline is based on an integrated plan for CERN, while the 3 TeV muon collider is explicitly a technically limited plan which assumes that a sufficient funding profile can be provided, and that there are no external constraints that could impact deployment. In other words, the muon-collider timeline remains an aspiration, whereas the FCC-ee timeline attempts to build-in actual deployment constraints.

What is the estimated cost of a 10 TeV muon collider?

At present, the cost estimates rely on broad extrapolations from existing collider systems. While these extrapolations suggest that a multi-TeV muon collider may well be one of the most cost-effective routes to the energy frontier, the uncertainties remain large. To deliver a “realistic” cost estimate, we will require a complete end-to-end reference design, engineering conceptual designs for all of the unique systems required, detailed cost estimates for the engineering conceptual designs and extrapolated cost estimates for the remaining “standard” accelerator systems. With the present technically limited schedule as prepared by the IMCC, this would suggest that a detailed and realistic cost estimate could be available around the end of this decade.

How does a high-energy muon collider fit into the global picture?

There are multiple ways this can fit. At present, we need to acknowledge that the R&D for the magnets for a high-energy proton–proton machine, such as those being pursued in Europe and China, still require an extensive R&D programme. This is likely a multi-decade effort in and of itself, and is commensurate with the timescales needed to carry out muon-collider R&D and design work. Having more than one technology option on the table to achieve our ultimate physics goals is a necessity. Furthermore, the complementarity between lepton- and hadron-collider paths may be needed to support our overarching scientific goals.

A detailed and realistic cost estimate could be available around the end of this decade

From a somewhat different point of view, the potential applications of a high-intensity muon source extend beyond colliders. The technology offers improved performance and new opportunities for other scientific goals such as a high-performance source for future neutrino and charged lepton flavour violation experiments, materials science and active interrogation of complex structures, among others. Clarifying the broader context for the technology is currently being pursued within the IMCC effort.

The post Shooting for a muon collider appeared first on CERN Courier.

Using multi-resolution propagation phase-contrast X-ray microtomography, a non-destructive technique widely used at the ESRF for palaeontology, the team was able to reconstruct a 3D image of the violin at the level of its cellular structure. In addition to revealing Il Cannone’s conservation status and structure, the results hint at the interventions made by luthiers throughout the instrument’s life.

In few months, we will be able to work on much larger instruments, up to the size of a double bass

Paul Tafforeau, ESRF

Inaugurated in 1994, the ESRF was the first “third generation” synchrotron, using periodic magnetic arrays called undulators to deliver the world’s brightest X-ray beams. It consists of a 844 m-circumference 6 GeV electron storage ring with almost 50 experimental stations serving around 5000 users per year across a wide range of disciplines. The study of Paganini’s violin was made possible by an EUR 330 million upgrade called the Extremely Brilliant Source, which came online in 2020. With an increased X-ray brightness and coherent flux 100 times higher than before, the facility allows complex materials to be imaged more quickly and in greater detail.

“We had to deal with some logistical and technical challenges, but the ESRF team did an incredible job to make this dream a reality,” says Paul Tafforeau, ESRF scientist in charge of BM18. “I hope that this experiment will be the first in a long series. In few months, we will be able to work on much larger instruments, up to the size of a double bass.”

The post Extremely Brilliant Source illuminates Paganini’s favourite violin appeared first on CERN Courier.

The workshop gathered almost 200 scientists and engineers in a hybrid format. Students, including undergraduates, and early-career researchers were strongly represented, as were key industry partners. A strong aim of the conference was to engage scientific communities outside particle physics to develop areas where the tools and techniques from particle physics could be game-changing.

The workshop focused on current and emerging techniques and scientific applications for deep learning and inference acceleration, including novel methods for efficient algorithm design, ultrafast on-detector inference and real-time systems. Acceleration as a service, hardware platforms, coprocessor technologies, distributed learning and hyper-parameter optimisation. The four-day event consisted of three workshop-style days with invited and contributed talks, and a final day dedicated to technical demonstrations and satellite meetings.

The tools and techniques from particle physics could be game-changing

The interdisciplinary nature of the workshop – which encompassed particle physics, free electron lasers, nuclear fusion, astrophysics, computer science and biology – made for a varied and interesting agenda. Attendees heard talks on how fast machine learning is being harnessed to speed up the identification of gravitational waves, and how it is needed to handle the high data rates and fast turnaround of experiments at free-electron lasers. In the medical arena, speakers addressed the need for faster image processing and data analysis for diagnosis and treatment, and the use of fast machine learning in biology to search for known and unknown features in large, heterogeneous datasets. The use of machine learning in control systems and simulations was discussed in the context of laser-driven accelerators and nuclear-fusion experiments, while in theoretical physics the application of machine learning to solve the electron wave equation in condensed matter, working towards a detailed and fundamental understanding of superconductivity, was presented.

Industry partners including AMD, Graphcore, Groq and Intel discussed current- and future-generation hardware platforms and architectures, and facilitated tutorials on their development toolchains. Researchers from Groq and Graphcore presented their latest dedicated chips for artificial-intelligence applications and showed that they have interesting applications to problems in particle physics, weather forecasting, protein folding, fluid dynamics, materials science and solving partial differential equations. AMD and Intel demonstrated the flexibility of their FPGA platforms and explained how to optimise them for scientific machine-learning applications.

A highlight of the social programme was a public lecture from Grammy Award-winning rapper Lupe Fiasco, who discussed his work with Google on large-language models. The workshop will return to the US next year, before landing in Zurich in 2025.

The post Machine-learning speedup for HL-LHC appeared first on CERN Courier.

The first ICFA Beam Dynamics workshop on Cold Copper Accelerator Technology and Applications was held at Cornell University from 31 August to 1 September 2023. Nearly 100 people came together to discuss the technology and explore next directions for R&D. Originally conceived at SLAC as an attractive approach to a linear-collider Higgs factory (dubbed the Cool Copper Collider, C³), interest in the technology has expanded to other areas.

Following opening presentations by Julia Thom-Levy (Cornell associate vice provost for research and innovation) and Jared Maxson (who leads the cold copper programme at Cornell), Emilio Nanni (SLAC) presented an overview of radio-frequency (RF) breakthroughs using cold copper cavities. He described three major advantages over conventional materials such as superconducting niobium: increased material conductivity at cryogenic temperatures (a reduction in resistance by a factor of three), significant reduction in pulsed heating, and improved yield strength and thermal diffusion. Combined, these lead to a high potential acceleration gradient of 70–120 MV/m, and an estimated 8 km footprint for a 550 GeV Higgs factory.

The optimised C-band cavity design enables a novel coupling of RF signals into each of the 40 cells along the cavity. A 9 m-long cryomodule would provide 1 GeV of acceleration. Some challenges identified for future R&D in the coming years are vibration control, meeting linac alignment specifications of 10 microns, and reducing the cost via optimised RF. Other applications of cold-copper technology include an ultra-compact free-electron laser (FEL) with 10–100 fs timing resolution as well as synergies with other proposed colliders such as ILC and FCC, where it could be used for positron production or as an injector, respectively. Walter Wuensch (CERN) summarised the extensive work over the past two decades on high-field limitations to copper performance. Breakdowns, field emission current and pulsed heating are fundamental limitations to performance, along with some practical ones such as limited RF power, conditioning time, small-aperture requirements, wakefields, power feeds and cooling capacity. Wuensch concluded that the community has a reasonably good understanding of copper, but that the demands for higher gradients and more performant cavities require careful optimisation.

The accelerator R&D community has a reasonably good under-standing of copper, but the demands for higher gradients and more performant cavities require careful optimisation

The workshop also delved into the details of cryomodule design, fabrication and damping, as well as the progress of relevant developments at LANL and INFN Frascati. Numerous industry participants gave presentations, including researchers from Radiabeam, Scandinova, Canon, EEC Permanent Magnets and Calabazas Creek.

Day two started with Caterina Vernieri (SLAC) presenting the C³ ambition for a Higgs factory based on extensive, recently published studies. Jamie Rosenzweig (UCLA) presented the design for an ultra-compact FEL and Paul Gueye (Michigan State) provided an overview of a potential high-gradient linac at the Facility for Rare Isotope Beams. Sami Tantawi (SLAC) presented potential medical applications of the technology, aimed at FLASH and very-high-energy-electron treatment modalities. Xi Yang (BNL) reviewed ultrafast electron diffraction devices and how moving from keV to MeV energies using compact copper accelerators could open new research opportunities. A session devoted to sustainability at CERN was covered by Maxim Titov (CEA Saclay), while Sarah Carsen (Cornell) presented the renewable programme at Cornell, which includes lake-source cooling of the campus and CESR accelerator complex, 28 MW of installed solar power, as well as geothermal plans. The successful mini-workshop concluded with a request to complete a report summarising the R&D discussions and post them on the Indico workshop site.

The accelerator R&D community awaits the P5 report (see p7) and the resulting strategies of the Department of Energy and National Science Foundation for accelerator research over the next decade.

The post Keeping it cool at Cornell appeared first on CERN Courier.

It is into this landscape that the CERN Accelerator School (CAS) was born in 1983. CAS lectures at that time were based on hand-written transparencies, sometimes pictures and sketches, or transparency copies from books. On some occasions, the transparencies were “hot off the press”, edited only the night before the presentation, using whisky as a solvent for the ink, with some traces remaining quite visible. The CAS lectures had to fulfil several objectives, notably the communication of deep knowledge and how to team-build at a time when significant progress could still be achieved by a single inventive scientist.

During the decades since, there has been a continuous evolution of the field of accelerators, driven by the rapid development of computing and telecommunications, and by the need for higher performance, leading to tighter tolerances or even novel acceleration technologies. Nowadays, much of the necessary information is only a mouse-click away, at any moment, at any location. Video, telephone and messenger exchanges are part of daily practice. The available computing power allows researchers to carry out complex simulations of beam behaviour by tracking thousands of particles over millions of turns in a reasonable time. No single accelerator component is built without extensive computer simulations beforehand, and the available simulation tools are extremely powerful and reliable. They do not yet, however, replace an innovative mind.

Collaboration

In this context, the present-day CAS has to play a new and even more demanding role. Knowledge about accelerators is available to every participant well before a CAS course begins. The multitude of information is enormous, which means that each CAS course, in particular the annual introductory course on accelerator physics, has to concentrate on the essential elements. Lecturers certainly have to be experts in their domain, but they also must have the capacity to explain their topic in simple terms.

The concept of the ingenious physicist designing an accelerator all by themselves also belongs in the past. Today, any new accelerator is the result of international collaborations featuring many individual contributions. CAS supports this development concept by fostering collaboration right from the start of the initial courses, ensuring that the students work in teams and that the links established during the courses are maintained throughout their professional lives.

The 40th anniversary of CAS offers an ideal opportunity to reflect on the school’s history, its educational approach, its impact and its bright future.

The seeds for the CERN Accelerator School were sown in the early 1980s by a group of visionary scientists and engineers at CERN. Driven by the high specialisation of the field, this group recognised the need for a dedicated educational programme that could provide comprehensive training in the rapidly evolving field of accelerator physics and technology. Textbooks on accelerator physics were sparse at the time, and courses at universities were practically non-existent. As Herwig Schopper, CERN Director-General at the time, put it: “An enormous amount of expertise is stored in the brains of quite a number of people […]. However, very little of this knowledge has so far been documented or published in book form.”

The first CAS course took place in Geneva in 1983 and attracted an impressive 107 participants. It focused on the special topic of colliding antiprotons. The W and Z bosons had just been discovered at CERN’s Super Proton–Antiproton Synchrotron (SppS), making this topic fully justified, as Kjell Johnson, the first CAS head, noted in his opening speech. This course was followed just a year later by a general one in accelerator physics, which is a classic today and remains one of the pillars of CAS. The general physics course covers topics such as beam dynamics, magnet technology, beam diagnostics, radiofrequency and vacuum systems. In this way, the school represents various types of accelerators and different accelerator components.

As the demand for specialised knowledge in accelerator physics grew, so did the CAS curriculum. While historically courses were more focused on high-energy colliders for particle physics, the scope broadened due to the development of applications in other fields, such as light sources, industry use and medicine. Over the years, the school has introduced a wide range of new topical courses to its portfolio, including radiofrequency systems, beam diagnostics, normal- and superconducting magnets, general superconductivity and cryogenics, vacuum systems and technology, high-gradient wakefield acceleration, high-intensity accelerators, medical accelerators and many more. This diversification has ensured that all participants are provided with up-to-date training in the latest developments. The curricula of the courses in “General Introduction to Accelerator Physics” and “Advanced Accelerator Physics” are also constantly adapting to the evolving landscape.

The success of CAS in Europe quickly caught the attention of the global accelerator community, leading to a surge in demand for its courses. To accommodate this growing interest, CAS began organising courses outside Europe from 1985 in collaboration with other institutions and organisations working in accelerator physics, such as the US Particle Accelerator School (USPAS), as well as the Joint Institute for Nuclear Research (JINR) in Russia and the High Energy Accelerator Research Organization (KEK) in Japan. Since then, these joint schools have trained more than 1000 participants via 16 courses in Asia, Europe and the Americas.

Educational approach

A key factor to the school’s success has been its innovative educational approach and the flexibility to adapt to new learning processes. Participants attend lectures delivered by selected lecturers, including some of the world’s foremost experts in accelerator physics, who willingly share their knowledge and insights in an engaging and accessible manner. By recognising the diverse backgrounds and needs of its participants, CAS offers courses at both the introductory and advanced physics levels. The former provide a solid foundation in the fundamental concepts of accelerator physics and technology, while the latter cater to participants with prior experience, act as a motivating refresher, or offer a deeper dive into specialised topics and the latest developments.

Today’s CAS experience is not limited to classroom lectures. The extensive availability of powerful computational tools has led to the introduction of hands-on sessions, first introduced in 2001, during which participants are not only put in touch with experimental set-ups but also dedicated expert-tool programmes. Particle-tracking codes or numerical-simulation programmes are examples where the participants are exposed to case studies and challenged to solve actual problems with expert guidance. Today, the introductory course offers hands-on software training in transverse and longitudinal beam dynamics as a regular course session. The advanced course, on the other hand, offers practical insight into beam optics as well as accelerator components from radiofrequency to beam diagnostics. Truckloads of equipment are shipped to the course venues, and the most recent topical CAS course on normal and superconducting magnets brought set-ups to perform superconducting experiments cooled down with liquid nitrogen to provide a real laboratory frame for teaching.

The heart of the CAS educational approach is clearly beating for an emphasis on problem-solving and collaborative learning. Participants are encouraged to work together on exercises and projects, fostering a sense of community and teamwork that extends beyond the classroom. It is the CAS spirit to work hand-in-hand with colleagues from different fields to solve a given task, very much as in a real work setting. This collaborative atmosphere not only enhances the learning experience but also offers the opportunity to build lasting relationships and to lay the ground for professional networks among participants. Throughout the CAS courses, participants profit from direct contact with the lecturers and their availability. Almost every lecturer has fond memories of long evening discussions with particularly interested participants – often fruitful for both sides. Equally legendary are the midnight hands-on sessions, carried out on request when all of a sudden another interest peak is sparking.

More to come

As the CERN Accelerator School celebrates its 40th anniversary, it is clear that its legacy of excellence, innovation and collaboration has left an indelible mark on the world of accelerator physics and technology. CAS has been instrumental in nurturing generations of experts who are continuing to push the boundaries of scientific knowledge, contributing significantly to our understanding of the universe. Over its 40 year-long history, more than 6000 participants from across the globe have been trained. Many of its alumni have gone on to play crucial roles in the development, construction and operation of particle accelerators around the world, including the LHC, to date still the largest machine ever built. However, no celebration would be complete without a projection into an even more promising future.

The variety of accelerator technologies, as much as the diversity and complexity of accelerator theory, will continue to grow. While the pre-education at European universities concerning basics in mathematics, electronics or computing already varies significantly between countries, worldwide collaborations make this aspect even more of a challenge. Over the years, the CAS teams have noticed, in particular in the introductory physics course, an ever-increasing spread in the basic accelerator-related knowledge that participants bring. Consequently, the CAS curriculum has been revised, but the problem persists: some participants are overwhelmed by the complexity of the course materials, whereas another large fraction is happily satisfied with the course and the progress they are able to make. As a first measure, the presently non-residential one-week “basic” CAS course on accelerator physics and technology will now be held on a yearly basis, and future participants of the introductory physics course will be strongly recommended to follow the basic CAS course first. If required, further adjustments for the general physics course will be made in the years to come.

With the ever-increasing diversity in technological disciplines and related scientific descriptions, CAS has stepped up the number of courses from two to four per year and, in addition, to offer at least two topical CAS courses per year. This allows the school to keep pace with the fast technological progress by teaching the major accelerator technologies (beam instrumentation, accelerator magnets, radiofrequency and superconductivity) roughly every five years, compared to every 10 years previously. While from a financial and organisational point of view four courses per year seem to be the maximum that can be offered, with the strong support of the CERN management this established rhythm can be maintained. In keeping with the long CAS tradition of publishing comprehensive proceedings for most of the courses, the higher frequency of courses has significantly increased the associated workload for authors and editors. Nevertheless, experience shows that these proceedings are vital to support the “post learning-process” of the CAS participants.

CAS has been instrumental in nurturing generations of experts who are continuing to push the boundaries of scientific knowledge

Finally, two years ago, a project called CASopedia was launched to record the CAS lectures. Fully in line with the CAS spirit, CASopedia aims to complement the regular written proceedings with a new learning approach where all recorded CAS lectures will be equipped with a catalogue of keywords and associated software with competent markers that allows topics to be searched via a keyword marker directly in the video material. Although a lot of work on this has already been done, significant effort is still needed to insert the many video-markers and to link them with the keyword database and the related time-code marker.

With these prospects in mind, and a rich legacy to build on, the school will undoubtedly continue to play a crucial role in the development of accelerator science by ensuring that future generations of physicists, engineers and technicians are well-equipped to tackle the ongoing challenges as well as the vast opportunities that always lie ahead. In this sense: happy birthday CAS, with hopes for an even bigger party to come in 10 years’ time!

The post 40 years of accelerating knowledge appeared first on CERN Courier.

Ten years ago, a group from Forsch­ungszentrum Jülich and Heinrich-Heine University Düsseldorf in Germany proposed a concept for producing highly polarised electron, proton or ion beams through plasma acceleration based on the use of polarised targets. Here the spins of the particles to be accelerated are already aligned before plasma formation. Although the method seems simple in principle, it requires careful consideration of various technical challenges associated with maintaining and utilising polarisation in a plasma environment. After all, spin alignments typically require low temperatures, making it counter-intuitive that they could endure in a 10⁸ K plasma for long enough to have practical applications.

A 2020 theoretical study of the scaling laws for the depolarisation times revealed the feasibility of polarised particle acceleration in strong plasma fields. Dozens of numerical simulations led to the conclusion that polarised beams from plasma acceleration should be within reach, with hadron beams requiring the simplest implementation. This is because hadrons have much smaller magnetic moments and, therefore, their spin alignment in the plasma magnetic fields is much more inert compared to electrons. Also, from the target point-of-view, polarised nuclei can be provided more easily than electrons.

In an experiment at the PHELIX petawatt laser at GSI Darmstadt, the Jülich–Düsseldorf group has now provided the first evidence for an almost complete persistence of nuclear polarisation after plasma acceleration to MeV energies. The group used an up-to 50% polarised ³He gas-jet target, which was irradiated by 2.2 ps laser pulses each with an energy of about 50 J. The polarisation of the accelerated ³He ions was measured with two identical polarimeters, optimised for short ion bunches from plasma acceleration and mounted perpendicular to the laser axis. For those cases where the nuclear spins in the target gas were aligned perpendicular to the flight direction of the helium ions, an angular asymmetry of the scattered particles in the polarimeters was observed, which is in line with a transversal polarisation of the accelerated ³He ions. No such asymmetries were found for the unpolarised gas.

The team now plans to repeat the experiments at PHELIX with higher gas polarisation and the use of a shorter (0.5 mm instead of 1.0 mm) gas-jet target. This would have the advantage that the ³He ions are dominantly emitted in the direction of the laser beam and at significantly higher energies (10–15 MeV). “For even higher laser intensities (> 10 PW), we have proposed a scheme based on shock acceleration to produce > 100 MeV polarised ³He beams,” says Markus Büscher of Jülich. “Also, a polarised hydrogen-chloride gas target for laser- or beam-driven acceleration of polarised proton and electron beams is being developed.”

The post Plasma accelerators target polarised beams appeared first on CERN Courier.

Following the completion of the second long shutdown (LS2) in 2022, during which the LHC injectors upgrade project was successfully implemented, Run 3 commenced at a record centre-of-mass energy of 13.6 TeV. Only two years of operation remain before the start of LS3 in 2026. This is when the main installation phase of the HL-LHC will commence, starting with the excavation of the vertical cores that will link the LHC tunnel to the new HL-LHC galleries and followed by the installation of new accelerator components. Approved in 2016, the HL-LHC project is driving several innovative technologies, including: niobium-tin (Nb₃Sn) accelerator magnets, a cold powering system made from MgB₂ high-temperature superconducting cables and a flexible cryostat, the integration of compact niobium crab cavities to compensate for the larger beam crossing angle, and new technology for beam collimation and machine protection.

Efforts at CERN and across the HL-LHC collaboration are now focusing on the series production of all project deliverables in view of their installation and validation in the LHC tunnel. A centrepiece of this effort, which involves institutes from around the world and strong collaboration with industry, is the assembly and commissioning of the new insertion-region magnets that will be installed on either side of ATLAS and CMS to enable high-luminosity operations from 2029. In parallel, intense work continues on the corresponding upgrades of the LHC detectors: completely new inner trackers will be installed by ATLAS and CMS during LS3 (CERN Courier January/February 2023 p22 and 33), while LHCb and ALICE are working on proposals for radically new detectors for installation in the 2030s (CERN Courier March/April 2023 p22 and 35).

Civil-engineering complete

The targeted higher performance at the ATLAS and CMS interaction points (IPs) demands increased cooling capacity for the final focusing quadrupole magnets left and right of the experiments to deal with the larger flux of collision debris. Additional space is also needed to accommodate new equipment such as power converters and machine-protection devices, as well as shielding to reduce their exposure to radiation, and to allow easy access for faster interventions and thus improved machine availability. All these requirements have been addressed by the construction of new underground structures at ATLAS and CMS. Both sites feature a new access shaft and cavern that will house a new refrigerator cold box, a roughly 400 m-long gallery for the new power converters and protection equipment, four service tunnels and 12 vertical cores connecting the gallery to the existing LHC tunnel. A new staircase at each side of the experiment also connects the new underground structures to the existing LHC tunnel for personnel.

Civil-engineering works started at the end of 2018 to allow the bulk of the interventions requiring heavy machinery to be carried out during LS2, since it was estimated that the vibrations would otherwise have a detrimental impact on the LHC performance. All underground civil-engineering works were completed in 2022 and the construction of the new surface buildings, five at each IP, in spring 2023. The new access lifts encountered a delay of about six months due to some localised concrete spalling inside the shafts, but the installation at both sites was completed in autumn 2023.

The installation of the technical infrastructures is now progressing at full speed in both the underground and surface areas (see “Buildings and infrastructure” image). It is remarkable that, even though the civil-engineering work extended throughout the COVID-19 shutdown period and was exposed to market volatility in the aftermath of Russia’s invasion of Ukraine, it could essentially be completed on schedule and within budget. This represents a huge milestone for the HL-LHC project and for CERN.

A cornerstone of the HL-LHC upgrade are the new triplet quadrupole magnets with increased radiation tolerance

A cornerstone of the HL-LHC upgrade are the new triplet quadrupole magnets with increased radiation tolerance. A total of 24 large-aperture Nb₃Sn focusing quadrupole magnets will be installed around ATLAS and CMS to focus the beams more tightly, representing the first use of Nb₃Sn magnet technology in an accelerator for particle physics. Due to the higher collision rates in the experiments, radiation levels and integrated dose rates will increase accordingly, requiring particular care in the choice of materials used to construct the magnet coils (as well as the integration of additional tungsten shielding into the beam screens). In order to have sufficient space for the shielding, the coil apertures need to be roughly doubled compared to the existing Nb-Ti LHC triplets, thus reducing the β^* parameter (which relates to the beam size at the collision points) by a factor of four compared to the nominal LHC design and fully exploiting the improved beam emittances following the upgrade of the LHC injector chain.

For the HL-LHC, reaching the required integrated magnetic gradient with Nb-Ti technology and twice the magnet aperture would require a much longer triplet. Choosing Nb₃Sn allows fields of 12 T to be reached, and therefore a doubling of the triplet aperture while keeping the magnet relatively compact (the total length is increased from 23 m to 32 m). Intensive R&D and prototyping of Nb₃Sn magnets started 20 years ago under the US-based LHC Accelerator Research Program (LARP), which united LBNL, SLAC, Fermilab and BNL. Officially launched as a design study in 2011, it has since been converted into the Accelerator Upgrade Program (AUP, which involves LBNL, Fermilab and BNL) in the industrialisation and series-production phase of all main components.

The HL-LHC inner-triplet magnets are designed and constructed in a collaboration between AUP and CERN. The 10 (eight for installation and two spares) Q1 and Q3 cryo-assemblies, which contain two 4.2 m-long individual quadrupole magnets (MQXFA), will be provided as an in-kind contribution from AUP, while the 10 longer versions for Q2 (containing a single 7.2 m-long quadrupole magnet, MQXFB, and one dipole orbit-corrector assembly) will be produced at CERN. The first of these magnets was tested and fully validated in the US in 2019 and the first cryo-assembly consisting of two individual magnets was assembled, tested and validated at Fermilab in 2023. This cryo-assembly arrived at CERN in November 2023 and is now being prepared for validation and testing. The US cable and coil production reached completion in 2023 and the magnet and cryo-assembly production is picking up pace for series production. 

The first three Q2 prototype magnets showed some limitations. This prompted an extensive three-phase improvement plan after the second prototype test to address the different stages of coil production, the coil and stainless-steel shell assembly procedure, and welding for the final cold mass. All three improvement steps were implemented in the third prototype (MQXFBP3), which is the first magnet that no longer shows any limitations, neither at 1.9 K nor 4.5 K operating temperatures, and thus the first from the production that is earmarked for installation in the tunnel (see “Quadrupole magnets” image).

Beyond the triplets, the HL-LHC insertion regions require several other novel magnets to manipulate the beams. For some magnet types, such as the nonlinear corrector magnets (produced by LASA in Milan as an in-kind contribution from INFN), the full production has been completed and all magnets have been delivered to CERN. The new separation and recombination dipole magnets – which are located on the far side of the insertion regions to guide the two counterrotating beams from the separated apertures in the arc onto a common trajectory that allows collisions at the IPs – are produced as in-kind contributions from Japan and Italy. The single-aperture D1 dipole magnets are produced by KEK with Hitachi as the industrial partner, while the twin-aperture D2 dipole magnets are produced in industry by ASG in Genoa, again as an in-kind contribution from INFN. Even though both dipole types are based on established Nb-Ti superconductor technology (the workhorse of the LHC), they push the conductor into unchartered territory. For example, the D1 dipole features a large aperture of 150 mm and a peak dipole field of 5.6 T, resulting in very large forces in the coils during operation. Hitachi has already produced three of the six series magnets. The prototype D1 dipole magnet was delivered to CERN in 2023 and cryostated in its final configuration, and the D2 prototype magnet has been tested and fully validated at CERN in its final cryostat configuration and the first series D2 magnet has been delivered from ASG to CERN (see “Dipole magnets” image).

A novel cold powering system featuring a flexible cryostat and MgB₂ cables can carry the required currents at temperatures of up to 50 K

Production of the remaining new HL-LHC magnets is also in full swing. The nested canted-cosine-theta magnets – a novel magnet design comprising two solenoids with canted coil layers, needed to correct the orbit next to the D2 dipole – is progressing well in China as an in-kind contribution from IHEP with Bama as the industrial partner. The nested dipole orbit-corrector magnets, required for the orbit correction within the triplet area, are based on Nb-Ti technology (an in-kind contribution from CIEMAT in Spain) and are also advancing well, with the final validation of the long-magnet version demonstrated in 2023 (see “Corrector magnets” image).

Superconducting link

With the new power converters in the HL-LHC underground galleries being located approximately 100 m away from and 8 m above the magnets in the tunnel, a cost- and energy-efficient way to carry currents of up to 18 kA between them was needed. It was foreseen that “simple” water-cooled copper cables and busbars would lead to an undesirable inefficiency in cooling-off the Ohmic losses, and that Nb-Ti links requiring cooling with liquid helium would be too technically challenging and expensive given the height difference between the new galleries and the LHC tunnel. Instead, it was decided to develop a novel cold powering system featuring a flexible cryostat and magnesium-diboride (MgB₂) cables that can carry the required currents at temperatures of up to 50 K.

With this unprecedented system, helium boils off from the magnet cryostats in the tunnel and propagates through the flexible cryostat to the new underground galleries. This process cools both the MgB₂ cable and the high-temperature superconducting current leads (which connect the normal-conducting power converters to the superconducting magnets) to nominal temperatures between 15 K and 35 K. The gaseous helium is then collected in the new galleries, compressed, liquefied and fed back into the cryogenic system. The new cables and cryostats have been developed with companies in Italy (ASG and Tratos) and the Netherlands (Cryoworld), and are now available as commercial materials for other projects (CERN Courier May/June 2023 p37).

Three demonstrator tests conducted in CERN’s SM18 facility have already fully validated the MgB₂ cable and flexible-cryostat concept. The feed boxes that connect the MgB₂ cable to the power converters in the galleries and the magnets in the tunnel have been developed and produced as in-kind contributions with the University of Southampton and Puma as industrial partner in the UK and the University of Uppsala and RFR as industrial partner in Sweden. A complete assembly of the superconducting link with the two feed boxes has been assembled and is being tested in SM18 in preparation for its installation in the inner-triplet string in 2024 (see “Superconducting feed” image).

IT string assembly

The inner-triplet (IT) string – which replicates the full magnet, powering and protection assembly left of CMS from the triplet magnets up to the D1 separation dipole magnet – is the next emerging milestone of the HL-LHC project (see “Inner-triplet string” image). The goal of the IT string is to validate the assembly and connection procedures and tools required for its construction. It also serves to assess the collective behaviour of the superconducting magnet chain in conditions as close as possible to those of their later operation in the HL-LHC, and as a training opportunity for the equipment teams for their later work in the LHC tunnel. The IT string includes all the systems required for operation at nominal conditions, such as the vacuum (albeit without the magnet beam screens), cryogenics, powering and protection systems. The installation is planned to be completed in 2024, and the main operational period will take place in 2025.

The entire IT string – measuring about 90 m long – just fits at the back of the SM18 test hall, where the necessary liquid-helium infrastructure is available. The new underground galleries are mimicked by a metallic structure situated above the magnets. The structure houses the power converters and quench-protection system, the electrical disconnector box, and the feed box that connects the superconducting link to normal-conducting powering systems. The superconducting link extends from the metallic structure above the magnet assembly to the D1 end of the IT string where (after a vertical descent mimicking the passage through the underground vertical cores) it is connected to a prototype of the feed box that connects to the magnets.

The inner-triplet string  is the next emerging milestone of the HL-LHC project

The installation of the normal-conducting powering and machine-protection systems of the IT string is nearing completion. Together with the already completed infrastructures of the facility, the complete normal-conducting powering system of the string entered its first commissioning phase in December 2023 with the execution of short-circuit tests. The cryogenic distribution line for the IT string has been successfully tested at cold temperatures and will soon undergo a second cooldown to nominal temperature, ahead of the installation of the magnets and cold-powering system this year.

Collimation

Controlling beam losses caused by high-energy particles deviating from their ideal trajectory is essential to ensure the protection and efficient operation of accelerator components, and in particular superconducting elements such as magnets and cavities. The existing LHC collimation system, which already comprises more than 100 individual collimators installed around the ring, needs to be upgraded to address the unprecedented challenges brought about by the brighter HL-LHC beams. Following a first upgrade of the LHC collimation and shielding systems deployed during LS2, the production of new insertion-region collimators and the second batch of low-impedance collimators is now being launched in industry.

LS2 and the subsequent year-end technical stop also saw the completion of the novel crystal-collimation scheme (CERN Courier November/December 2022 p35). Located in “IR7” between CMS and LHCb, this scheme comprises four goniometers with bent crystals – one per beam and plane – to channel halo particles onto a downstream absorber (see “Crystal collimators” image). After extensive studies with beam during the past few years, crystal collimation was used operationally in a nominal physics run for the first time during the 2023 heavy-ion run, where it was shown to increase the cleaning efficiency by a factor of up to five compared to the standard collimation scheme. Following this successful deployment and comprehensive machine-development tests, the HL-LHC performance goals have been conclusively confirmed for both proton and ion operations. This has enabled the baseline solution using a standard collimator inserted in IR7 (which would have required replacing a standard 8.3 T LHC dipole with two short 11 T Nb₃Sn dipoles to create the necessary space) to be descoped from the HL-LHC project.

Crab cavities

A second cornerstone of the HL-LHC project after the triplet magnets are the superconducting radiofrequency “crab” cavities. Positioned next to the D2 dipole and the Q4 matching-section quadrupole magnet in the insertion regions, these are necessary to compensate for the detrimental effect of the crossing angle on luminosity by applying a transverse momentum kick to each bunch entering the interaction regions of ATLAS and CMS. Two different types of cavities will be installed: the radio-frequency dipole (RFD) and the double quarter wave (DQW), deflecting bunches in the horizontal and vertical crossing planes, respectively (see “Crab cavities” image). Series production of the RFD cavities is about to begin at Zanon, Italy under the lead of AUP, while the DQW cavity series production is well underway at RI in Germany under the lead of CERN following the successful validation of two pre-series bare cavities.

A fully assembled DQW cryomodule has been undergoing highly successful beam tests in the Super Proton Synchrotron (SPS) since 2018, demonstrating the crabbing of proton beams and allowing for the development and validation of the necessary low-level RF and machine-protection systems (CERN Courier March/April 2022 p45). For the RFD, two dressed cavities were delivered at the end of 2021 to the UK collaboration after their successful qualification at CERN. These were assembled into a first complete RFD cryomodule that was returned to CERN in autumn 2023 and is currently undergoing validation tests at 1.9 K, revealing some non-conformities to be resolved before it is ready for installation in the SPS in 2025 for tests with beams. Series production of the necessary ancillaries and higher-order-mode couplers has also started for both cavity types at CERN and AUP after the successful validation of prototypes. Prior to fabrication, the crab-cavity concept underwent a long period of R&D with the support of LARP, JLAB, UK-STFC and KEK.

On schedule

2023 and 2024 are the last two years of major spending and allocation of industrial contracts for the HL-LHC project. With the completion of the civil-engineering contracts and the placement of contracts for the new cryogenic compressors and distribution systems, the project has now committed more than 75% of its budget at completion. An HL-LHC cost-and-schedule review held at CERN in November 2023, conducted by an international panel of accelerator experts from other laboratories, congratulated the project on the overall good progress and agreed with the projection to be ready for installation of the major equipment during LS3 starting in 2026.

The major milestones for the HL-LHC project over the next two years will be the completion and operation of the IT-string installation in 2024 and 2025, and the completion of the installation of the technical infrastructures in the new underground galleries. All new magnet components should be delivered to CERN by the end of 2026, while the drilling of the vertical cores connecting the new and old underground areas should complete the major construction activities and mark the start of the installation of the new equipment in the LHC tunnel.

The HL-LHC will push the largest scientific instrument ever built to unprecedented levels of performance and extend the flagship collider of the European and US high-energy physics programme by another 15 years. It is the culmination of more than 25 years of R&D, with close cooperation with industry in CERN’s member states and the establishment of new accelerator technologies for the use of future projects. All hands are now on deck to ensure the brightest future possible for the LHC.

The post HL-LHC counts down to LS3 appeared first on CERN Courier.

Originally published in 2016, the first edition was picked up by CERN’s “eBooks for all!” programme to be converted to open access. The second edition, released in April 2023, has been updated throughout to cover new and essential areas in accelerator science. The material for the book originated from lectures and courses with the aim to teach undergraduate and graduate students several physics disciplines in a coherent way, while at the same time ensuring that this training would develop and stimulate innovativeness. It is written with a fine balance between technical rigour and a conversational tone, avoiding heavy mathematics and using back-of-the-envelope-type derivations and estimations wherever possible. This makes the book inspiring for both experts seeking in-depth knowledge and curious minds looking for an introduction to the field.

With the authors’ systematic approach, readers can easily follow the logical progression of ideas, facilitating comprehension and aiding future reference. They introduce the reader to the basics of accelerators and the art of inventiveness, and provide a solid foundation for understanding the key concepts of accelerators, lasers and plasma, and how they can be integrated and used together to advance scientific research.

The book includes a wide range of relevant topics such as beam dynamics, cavities, synchrotron radiation, laser and plasma physics and their role in accelerators. It then delves into advanced accelerator concepts such as radiation generation, wakefield acceleration and laser-plasma accelerators, free-electron lasers and plasma-based light sources. The authors also weave in the historical development of accelerator, laser and plasma technologies, highlighting milestones that have shaped the scientific landscape. They also extensively explore the next generation of accelerators, cutting-edge technologies and state-of-the-art facilities employed in these fields. New chapters added to the second edition, which are crucial in the accelerator area and relevant for future projects, include topics such as superconducting technology, beam cooling, final focusing, polarisation, beam stability, energy recovery, advanced technologies and no fewer than 40 inventive principles.

Also remarkable are the more than 380 illustrative diagrams that allow the reader to visualise the content for a better understanding. In the eBook most of the pictures have been changed to even more attractive colour versions.

The authors commit to scientific integrity, reinforcing their authority in the field. In addition, their pedagogical strength and clear aim to help the reader develop a deeper understanding of the material is emphasised with numerous end-of-chapter exercises. In the second edition, the guide to the solutions has been added directly into the book.

This book is the first of its kind where the three disciplines of accelerators, lasers and plasmas are connected towards building more compact accelerators. One of the highlights is the authors’ emphasis on the potential synergistic effects that can arise from integrating these three areas. With its accessible explanations, cutting-edge research coverage, and compelling arguments for interdisciplinary collaboration, this is an indispensable resource for physicists, researchers and students alike.

The post Connecting the accelerator dots appeared first on CERN Courier.

Following the successful repair in August of a small leak in the insulation vacuum of the LHC inner triplet assembly near Point 8, beams returned on 30 August for the first long heavy-ion run of Run 3. Stable beams were declared on 27 September with an energy of 5.36 TeV per nucleon pair (compared to 5.02 TeV during Run 2) and a collision rate increased by a factor of 10 since the last heavy-ion run in 2018.

The primary goal of the five-week-long run was to advance understanding of quark–gluon plasma, in which quarks and gluons move around freely for a split-second before the system expands and cools down, turning back into hadrons. In addition to the improved beam parameters, significant upgrades have taken place in the LHC experiments to maximise their physics harvest. ALICE is now using an entirely new mode of data processing, storing all collisions without selection, resulting in up to 100 times more collisions being recorded per second (CERN Courier September/October 2023 p39). In addition, its track reconstruction efficiency and precision have increased due to the installation of new subsystems and upgrades of existing ones. CMS and ATLAS have also upgraded their data acquisition, reconstruction and selection infrastructures to take advantage of the increased collision rates, while LHCb is preparing a unique programme of fixed-target collisions between lead nuclei and other types of nuclei using its SMOG2 apparatus.

The increased number of collisions is expected to allow measurements of the temperature of the quark–gluon plasma using thermal radiation in the form of photons and electron-positron pairs. Hydrodynamic properties of this near-perfect liquid state will also be measured in greater detail. In addition, the experiments will probe ultra-peripheral collisions of heavy ions in which one beam emits a high-energy photon that strikes the other beam. These collisions will be used to probe gluonic matter inside nuclei and to study rare phenomena such as light-by-light scattering and τ-lepton photoproduction.

The post Heavy ions return in style appeared first on CERN Courier.

With a wide programme of plenary and parallel sessions, the workshop was a great opportunity for the community to discuss current and future R&D directions, with a focus on sustainability, and was testament to the eagerness of physicists from all over the world to join forces to build the next Higgs factory. More than 200 scientists participated, about 30% of which were early-career researchers and industry partners.

Energy frontiers

As set out by the 2020 update of the European strategy for particle physics and the Energy Frontier report from Snowmass 2021, particle physicists agreed that precision Higgs-boson measurements are the best path toward further progress and to provide insights into potential new-physics interactions. The Higgs boson is central for understanding fundamental particles and interactions beyond the Standard Model. Examples include the nature of dark matter and matter–antimatter asymmetry, which led to the prevalence of matter in our universe. 

Ideally, data-taking at a future e⁺e^–Higgs factory should follow the HL-LHC directly, requiring construction to start by 2030, in parallel with HL-LHC data-taking. Any significant delay will put at risk the availability of essential and unique expertise, and human resources, and endanger the future of the field.

Among the e⁺e^– colliders being evaluated by the community, the International Linear Collider (ILC), based on superconducting RF technology, has the most advanced design. It is currently under consideration for construction in Japan. However, for a long time now, Japan has not initiated a process to host this collider. One alternative approach is to construct a large circular collider – a strategy now being pursued by CERN with the FCC-ee, and by China with the CEPC. Both colliders would require tunnels of about 100 km circumference to limit synchrotron radiation. The FCC-ee machine is foreseen to operate in 2048, seven years after the end of the HL-LHC programme, with a substantial cost in time and resources for the large tunnel. An alternative is to construct a compact linear e⁺e^– collider based on high-gradient acceleration. CERN has a longstanding R&D effort along these lines, CLIC, that would operate at a collision energy of 380 GeV. 

New technologies proposed for higher-energy stages will require decades of R&D

Given the global uncertainties around each proposal, it is prudent to investigate alternative plans based on technologies that could enable compact designs and possibly provide a roadmap to extend the energy reach of future colliders. As also highlighted in the Snowmass Energy Frontier report, consideration should be given to the timely realisation of a Higgs factory in the US as an international effort. For instance, the Cool Copper Collider (C³) is a new and even more compact proposal for a Higgs-producing linear collider. It was developed during Snowmass 2021 and made its debut at LCWS with more than 15 talks and five posters. This proposal would use normal-conducting RF cavities to achieve a collision energy of 500 GeV with an 8 km-long collider, making it significantly smaller and likely more cost-effective than other proposed Higgs factories.

There are many advantages of the linear approach. Among them, linear colliders are able to access energies of 500 GeV and beyond, while for circular e⁺e^– colliders the expected luminosity drops off above centre-of-mass energies of 350–400 GeV. This would allow precision measurements that are crucial for indirect searches for new physics, including measurements of the top-quark mass and electroweak couplings, the top-Higgs coupling, and the cross section for double-Higgs production.

At LCWS 2023, the community showed progress on R&D for both accelerator and detector technologies and outlined how further advances in ILC technology, as well as alternative technologies such as C³ and CLIC, promise lower costs and/or extended energy reach for later stages of this programme. Discoveries at a Higgs factory may point to specific goals for higher energy machines, with quark and lepton collisions at least 10 times the energies of the LHC. New technologies proposed for such higher-energy stages – using pp, muon and e⁺e^– colliders – will require decades of R&D. Construction and operation of a linear Higgs factory would be a key contribution towards this programme by developing an accelerator workforce and providing challenges to train young scientists.

In this regard, a key outcome of the SLAC workshop was a statement supporting the timely realisation of a Higgs factory based on a linear collider to access energies beyond 500 GeV and enable the measurements vital for new physics to the P5 committee, which is currently evaluating priorities in US high-energy physics for the next two decades.

The post Aligning future colliders at SLAC appeared first on CERN Courier.

The Future Circular Collider (FCC) offers a multi-stage facility – beginning with an e⁺e^– Higgs and electroweak factory (FCC-ee), followed by an energy-frontier hadron collider (FCC-hh) in the same 91 km tunnel – that would operate until at least the end of the century. Following the recommendation of the 2020 update of the European strategy for particle physics, CERN together with its international partners have launched a feasibility study that is due to be completed in 2025. FCC Week 2023, which took place in London from 5 to 9 June, and attracted about 500 people, offered an excellent opportunity to strengthen the collaboration, discuss the technological and scientific opportunities, and plan the submission of the mid-term review of the FCC feasibility study to the CERN Council later this year.

The FCC study, along with the support of the European Union FCCIS project, aims to build an ecosystem of science and technology involving fundamental research, computing, engineering and skills for the next generation. It was therefore encouraging that around 40% of FCC Week participants were aged under 40.

Working together

In his welcome speech, Mark Thomson (UK STFC executive chair) stressed the importance of a Higgs factory as the next tool in exploring the universe at a fundamental level. Indeed, one of the no-lose theorems of the FCC programme, pointed out by Gavin Salam (University of Oxford), is that it will shed light on the Higgs’ self-interaction, which governs the shape of the Brout–Englert–Higgs potential. In her plenary address, Fabiola Gianotti (CERN Director-General) confirmed that the current schedule for the completion of the FCC feasibility study is on track, and stressed that the FCC is the only facility commensurate with the present size of CERN’s community, providing up to four experimental points, concluding “we need to work together to make it happen”.

Designing a new accelerator infrastructure poses a number of challenges, from civil engineering and geodesy to the development of accelerator technologies and detector concepts to meet the physics goals. One of the major achievements of the feasibility study so far is the development of a new FCC layout and placement scenario, thanks to close collaboration with CERN’s host states and external consultants. As Johannes Gutleber (CERN) reported, the baseline scenario has been communicated with the affected communes in the surrounding area and work has begun to analyse environmental aspects at the surface-site locations. Synergies with the local communities will be strengthened during the next two years, while an authorisation process has been launched to start geophysical investigations next year.

Essential for constructing the FCC tunnel is a robust 3D geological model, for which further input from subsurface investigations into areas of geological uncertainty is needed. On the civil-engin­eering side, two further challenges include alignment and geodesy for the new tunnel. Results from these investigations will be collected and fed into the civil-engineering cost and schedule update of the project. Efforts are also focusing on optimising cavern sizes, tunnel widenings and shaft diameters based on more refined requirements from users.

Transfer lines have been optimised such that existing tunnels can be reused as much as possible and to ensure compatibility between the lepton and hadron FCC phases. Taking CERN’s full experimental programme into account, the option of using the SPS as pre-booster for FCC-ee will be consolidated and compared with the cost with a high-energy linac option.

A new generation of young researchers will need to take the reins to ensure FCC gets delivered and exploit the physics opportunities offered by this visionary research infrastructure

At the heart of the FCC study are sustainability and environmental impact. Profiting from an R&D programme on high-efficiency klystrons initially launched for the proposed Compact Linear Collider, the goal is to increase the FCC-ee klystron efficiency from 57% (as demonstrated in the first prototypes) to 80% – resulting in an energy saving of 300 GWh per year without considering the impact that this development could have beyond particle physics. Other accelerator components where work is ongoing to minimise energy consumption include low-loss magnets, SRF cavities and high-efficiency cryogenic compressors.

The FCC collaboration is also exploring ways in which to reuse large volumes of excavated materials, including the potential for carbon capture. This effort, which builds on the results of the EU-funded “Mining the Future” competition launched in 2020, aims to re-use the excavated material locally for agriculture and reforestation while minimising global nuisances such as transport. Other discussions during FCC Week focused on the development of a renewable energy supply for FCC-ee. 

If approved, a new generation of young researchers will need to take the reins to ensure FCC gets delivered and exploit the physics opportunities offered by this visionary research infrastructure. A dedicated early-career researcher session at FCC Week gave participants the chance to discuss their hopes, fears and experiences so far with the FCC project. A well-attended public event “Giant Experiments, Cosmic Questions” held at the Royal Society and hosted by the BBC’s Robin Ince also reflected the enthusiasm of non-physicists for fundamental exploration.

The highly positive atmosphere of FCC Week 2023 projected a strong sense of momentum within the community. The coming months will keep the FCC team extremely busy, with several new institutes expected to join the collaboration and with the scheduled submission of the feasibility-study mid-term review advancing fast ahead of its completion in 2025.

The post Towards a century of trailblazing physics appeared first on CERN Courier.

Following inspiring opening speeches by Antonio Zoccoli (INFN president) and Alfonso Franciosi (Elettra president) about the important role of particle accelerators in Italy, the scientific programme got under way. It included 87 talks and over 1500 posters covering all particles (electrons, positrons, protons, ions, muons, neutrons, …), all types of accelerators (storage rings, linacs, cyclotrons, plasma accelerators, …), all use-cases (particle physics, photon science, neutron science, medical and industrial applications, material physics, biological and chemical, …) and institutes involved across the world. The extensive programme offered such a wide perspective of excellence and ambition that it is only possible to highlight a short subset of what was presented.

Starting proceedings was a report by Malika Meddahi (CERN) on the successful LHC Injectors Upgrade (LIU) project. This project, with its predominantly female leadership team, was executed on budget and on schedule. It provides the LHC with beams of increased brightness as required by the ongoing luminosity upgrade, as later reported by CERN’s Oliver Brüning. The focus then shifted to advanced X-ray light sources. Emanuel Karantzoulis (Elettra) presented Elettra 2.0 – a new ultra-low emittance light source in construction in Trieste. Axel Brachmann (SLAC) updated participants on the status of LCLS-II, the world´s first CW X-ray free-electron laser (XFEL). While beam commissioning is somewhat delayed, the superconducting RF accelerator structures perform beyond the performance specification and the facility is in excellent condition. The week´s programme included an impressive overview by Dong Wang (Shanghai Advanced Research Institute) on the future of XFELs for which user demand has led to an enormous investment aiming in particular at “high average power”, which will be used to serve many more experiments including those for highly non-linear QED. Gianluca Geloni (European XFEL) showed that user operation for the world`s presently most powerful XFEL has been successfully enhanced with self-seeding. Massimo Ferrario (INFN) described the promise of a novel, high-tech plasma-based FEL being explored by the European EuPRAXIA project.

Jörg Blaurock (FAIR/GSI) presented the status of the €3.3 billion FAIR project. Major obstacles have been overcome and the completed tunnel and many accelerator components are now being prepared for installation, starting in 2024. The European Spallation Source in Sweden is advancing well and the proton linac is approaching full beam commissioning, as presented by Ryoichi Miyamoto (ESS) and Andrea Pisent (INFN). Yuan He from China (IMP, CAS) presented opportunities in accelerator-driven nuclear power, both in safety and in reusing nuclear fuels, and impressed participants with the news on a Chinese facility that is progressing well in terms of up-time and reliability. This theme was also addressed by Ulrich Dorda (Belgian Nuclear Research Centre) who presented the status of the Multi-purpose Hybrid Research Reactor for High-tech Applications (MYRRHA) project. Another impressive moment of the programme was Andrey Zelinsky’s (NSC in Ukraine) presentation on the Ukraine Neutron Source facility at the National Science Center “Kharkov Institute of Physics & Technology” (NSC KIPT). Construction, system checks and integration tests for this new facility have been completed and beam commissioning is being prepared under extremely difficult circumstances, as a result of Russia’s invasion.

Technological highlights included a report by Claire Antoine (CEA) on R&D into thin-film superconducting RF cavities and their potential game-changing role in sustainability. Sustainability was a major discussion topic throughout IPAC23, and several speakers presented the role of accelerators for the development of fusion reactors. The final talk of the conference by Beate Heinemann (DESY) showed that without accelerators, much knowledge in particle physics would still be missing and she argued for new accelerator facilities at the energy frontier to allow further discoveries.

The prize session saw Xingchen Xu (Fermilab), Mikhail Krasilnikov (DESY/Zeuthen) and Katsunobu Oide (KEK) receive the 2023 EPS-AG accelerator prizes. In addition, the Bruno Touschek prize was awarded to Matthew Signorelli (Cornell University), while two student poster prizes went to Sunar Ezgi (Goethe Universität Frankfurt) and Jonathan Christie (University of Liverpool).

IPAC23 included for the first time in Europe an equal opportunity session, which featured talks from Maria Masullo (INFN) and Louise Carvalho (CERN) on gender and STEM, pointing to the need to change the narrative and to move “from talk to targets”. The 300 participants in the session learnt about ways to improve gender balance but also about such important topics as neurodiversity. The very well attended industrial session of IPAC23 brought together projects and industry in a mixed presentation and round-table format.

For the organizers, IPAC23 has been a remarkable and truly rewarding effort, seeing the many delegates, industry colleagues and students from all over the world coming together for a lively, peaceful and collaborative conference. The many outstanding posters and talks promise a bright future for the field of particle accelerators.

The post Record attendance at IPAC23 appeared first on CERN Courier.

At around 1 a.m. on 17 July, the LHC beams were dumped after only nine minutes in collision due to a radiofrequency interlock caused by an electrical perturbation. Approximately 300 milliseconds after the beams were cleanly dumped, several superconducting magnets lost their superconducting state, or quenched. Among them were the inner-triplet magnets located to the left of Point 8, which focus the beams for the LHCb experiment. While occasional quenches of some LHC magnets are to be expected, the large forces resulting from this particular event led to a breach of the vacuum helium pressure vessel, rapidly degrading the insulation vacuum and prompting a series of interventions with implications for the 2023 Run 3 schedule. 

The leak occurred between the LHC’s cryogenic circuit, which contains the liquid helium, and the insulation vacuum that separates the cold magnet from the warm outer vessel (the cryostat) – a crucial barrier for preventing heat transfer from the surrounding LHC tunnel to the interior of the cryostat. As a result of the leak, the insulation vacuum filled with helium gas, cooling down the cryostat and causing condensation to form and freeze on the outside. 

By 24 July the CERN teams had traced the leak to a crack in one of more than 2500 bellows that compensate for thermal expansion and contraction on the cryogenic distribution lines. Measuring just 1.6 mm long, it is thought to have been caused by a sudden increase in vacuum pressure when the magnet quench protection system (QPS) kicked in. Following the electrical perturbation, the QPS had dutifully triggered the quench heaters (which are designed to bring the whole magnet out of the superconducting state in a controlled and homogenous manner) of the magnets concerned, generating a heat wave according to expectations.

It is the first time that such a breach  event has occurred; the teamwork between many working groups, including safety, accelerator operations, vacuum, cryogenics, magnets, survey, beam instrumentation, machine protection, electrical quality assurance as well as material and mechanical engineering, made a quick assessment and action plan possible. On 25 July the affected bellow was removed. A new bellow was installed on 28 July, the affected modules were closed, and the insulation vacuum was pumped. 

The electrical perturbation turned out to be caused by an uprooted tree falling on power lines in the nearby Swiss municipality of Morges. In early August, as the Courier went to press, the repairs were finished and the implications for Run physics were being assessed. The choice is between preparing the machine for a short-term proton–proton phase to account for some of the missed run time or sticking to the planned heavy-ion run at the end of the run year, since in 2022 there was no full heavy-ion run. The favoured scenario is to go with the latter and was presented to the LHC machine committee on 26 July.

The post Electrical perturbation uproots Run 3 operations appeared first on CERN Courier.

A recap of CERN’s SRF achievements is instructive at this point before unpacking the longer-term R&D and innovation roadmap. For starters, SRF cavities – a workhorse technology for frontier accelerators in particle physics, nuclear physics and materials science – were instrumental in pushing CERN’s Large Electron-Positron (LEP) collider to new energy regimes. Through the late 1990s, a total of 288 SRF cavities – each comprising a thin film of superconducting niobium sputtered onto a copper cavity – were installed in LEP-II, providing up to 7 MV/m of accelerating gradient and allowing the machine to eventually reach a centre-of-mass energy of 209 GeV (versus 91 GeV for the original LEP machine). At the start of the millennium, LEP-II was the most powerful SRF installation worldwide.

Fast forward to 2010 and the advent of the HIE-ISOLDE project, the “high-intensity and energy” upgrade to CERN’s radioactive beam facility, which unlocked further investment in the SRF programme. Operationally, HIE-ISOLDE was all about increasing the energy of ISOLDE’s radionuclide beams from 3 MeV/u up to 10 MeV/u through the construction of a superconducting post-accelerator – necessitating, in turn, the design, processing and testing of bulk-niobium SRF cavities along with improved coating performance for thin-film niobium–copper SRF cavities. 

CERN engineers duly developed a full prototype of the 100 MHz coated quarter-wave cavities for HIE-ISOLDE before spinning out the technology to industry. Subsequently, however, several of the outsourced cavities exhibited performance limitations, linked to a welding seam in a cavity region with high surface currents. To address this problem, CERN’s RF team came up with an innovative work-around that proved to be crucial in pushing the performance envelope of thin-film SRF cavities.

Put simply, the HIE-ISOLDE cavity was redesigned in such a way that it could be machined out of a single piece of copper with no welds. After coating with niobium and subsequent testing in 2017, the new-look cavity yielded unprecedented surface peak fields of over 60 MV/m and a Q value of 10⁹ at 2.3 K. These figures of merit – well above the qualification target of approximately 30 MV/m (Q = 5 × 10⁸) – gave a clear direction for further R&D on thin-film cavities on seamless copper substrates, with four cryomodules (each containing five SRF cavities) later installed as part of the HIE-ISOLDE upgrade. Significantly, this was also the first time that a “production” cavity using thin-film niobium on copper gave comparable results to bulk-niobium cavities, the performance of which had seen rapid advances over the previous decade as a result of the collective R&D effort geared towards the International Linear Collider (ILC). 

Crab cavities in the HL-LHC

Right now, front-and-centre on the SRF technology roadmap is the HL-LHC project, an ambitious undertaking to increase the integrated luminosity by a factor of 10 beyond the LHC’s design value and, in so doing, open up new opportunities for fundamental physics from 2030 onwards. Once operational, the HL-LHC will use superconducting bulk-niobium “crab cavities” to optimise the bunch crossing at the particle interaction points – thereby increasing and “levelling” the luminosity of the proton–proton collisions. This is achieved by turning the particle bunches slightly before collision and then returning them to their original orientation after the interaction (see “Crafted collisions”). 

At ATLAS and CMS, there will be two 400 MHz crab cavities deployed for each beam on each side of the experiments – i.e. a total of 16 cavities (eight cryomodules) will be installed during Long Shutdown 3 (LS3), starting in 2026. As the beampipes for the colliding beams are only 194 mm apart, an ultracompact cavity design is necessary to produce the required kick voltage of 3.4 MV per cavity. An intensive R&D effort – involving a network of international partners and funding sources – resulted in two final designs, one for horizontal crabbing (RF dipole, RFD) and one for vertical crabbing (double quarter-wave, DQW). These advanced cavity shapes are roughly four times more compact versus the elliptical LHC accelerating cavities and, as such, present significant challenges in terms of their fabrication. 

To test the envisaged technical concepts – and, by extension, demonstrate the crabbing of a proton beam – CERN’s RF development team carried out a beam test of two DQW cavities in the Super Proton Synchrotron (SPS) back in 2018 (CERN Courier May 2018 p18). After construction and processing at CERN, the cavities were subsequently assembled into a cryomodule at the SM18 test facility (a dedicated CERN site for evaluation of superconducting magnets and SRF cavities). 

To maximise workflow efficiency, the SPS test stand has a movable platform for the cryomodule, which is connected with flexible elements to the SPS beampipe. This arrangement makes it possible to move the cavities in and out of the beam and thereby reduce the impact on regular SPS operation. The beam tests validated not only the crabbing effect on the circulating proton beam, but also the design and engineering choices for these new cryomodules. 

It’s worth noting that the streamlined prototyping of the SPS DQW cryomodule was only possible thanks to CERN’s ongoing investment in SRF R&D and expertise. At a more granular level, that translates into a portfolio of core skillsets spanning niobium-sheet forming and welding; niobium surface chemistry with buffered chemical processing and electropolishing; surface cleaning with high-pressure ultrapure water; assembly of cavities in ISO4 clean rooms; preparation and conducting of cold tests at 2 K; as well as the clean assembly of cavity strings and their integration into full cryomodules with cutting-edge alignment precision.     

Collaborate, innovate, accelerate

Following the verification of the underlying technical concepts, CERN established a network of international collaborations for an initial consignment of 10 cryomodules for the HL-LHC plus a spare DQW module and spare RFD module. Division of labour is key here, with German manufacturer RI Research Instruments handling the fabrication and chemical processing of the DQW cavities. After cold-testing the bare cavities at CERN, they are sent back to RI to be equipped with a helium tank and cold magnetic shields, which are provided by Daresbury Laboratory in the UK as part of a joint effort between CERN and the UK’s Science and Technology Facilities Council (STFC). 

These so-called “jacketed” cavities return to CERN for another round of cold-testing before being fitted with higher-order-mode (HOM) RF couplers, manufactured in the CERN workshops. Once the performance of the now “dressed” cavities is validated, they are assembled into cryomodules at Daresbury before coming back to CERN for cold-test validation and installation.

Meanwhile, the production of RFD modules takes place in North America as part of the US HL-LHC Accelerator Upgrade Project (AUP) collaboration. In terms of specifics: Fermilab has contracted the Italian manufacturer Zanon for production of bare cavities, with the laboratory retaining responsibility for the chemical treatments, cold magnetic shields, helium vessel and HOM couplers. Fermilab scientists also conduct the cold-tests for the bare, jacketed and dressed cavities. Once the cavities reach the desired performance level, they are shipped to TRIUMF in Canada for re-testing and assembly into cryomodules.

Ensuring this complex collective endeavour remains on track is no small challenge, requiring implementation of well-defined technical interfaces and rigorous performance monitoring while also keeping tabs on day-to-day project scheduling, transportation and thorny logistics issues (including Brexit-related paperwork). More broadly, it’s worth noting that the experience gained from prototyping the crab cavities and cryomodules at CERN has enabled the RF team to establish a stringent quality-assurance system, subsequently shared with all our collaborators to ensure standardised production processes, workflows and system integration. 

Looking ahead, the next milestone for the HL-LHC crab cavity programme is the testing of the first RFD module in the SPS. Currently, this module is being assembled at Daresbury Laboratory and will be delivered to CERN in September 2023, after which it will be cold-tested in SM18 prior to installation in the SPS during the 2023/24 year-end technical stop.

While the crab-cavity programme will keep CERN’s RF team occupied until the conclusion of LS3 in 2028, preparations are already under way for the 2030s and beyond. Right now, there is a consensus that the next major collider after the LHC will be a lepton machine focused on precision measurements of the Higgs boson. In the case of a circular collider, this will necessitate a powerful RF system to attain collision energies surpassing those achieved by LEP. Two potential candidates are the electron-positron Future Circular Collider (FCC-ee), which would require over 1000 SRF cavities, and a muon collider with more than 3000 SRF cavities (for a 10 TeV centre-of-mass scenario). Meanwhile, a linear collider such as the proposed 500 GeV ILC would necessitate over 7000 SRF cavities. 

Progressions of power

Regardless of the eventual scenario, it is evident that the RF system poses a significant technological challenge, with most options involving deployment of SRF cavities at levels an order of magnitude greater than those used in LEP. With rising electricity prices, and growing calls for operational sustainability within high-energy physics, CERN has an obligation to pursue all means of reducing the power consumption of the next big collider. In this context, the CERN RF group is prioritising two strategic R&D objectives: to reduce the surface losses of superconducting cavities while engaging in higher-efficiency RF power generation. 

It’s instructive to consider CERN’s SRF strategy in the context of the FCC-ee – and specifically, the potential impact of reduced cavity losses on FCC-ee power consumption and how that is shaping SRF R&D priorities. The present FCC-ee scenario foresees four main stages of operation at increasing centre-of-mass energies, enabling precision measurements of the Z boson (91 GeV), W boson (161 GeV), Higgs boson (250 GeV) and the top quark (365 GeV). The high beam currents needed to support Z and W physics enforce the use of low-frequency cavities (400 MHz) to control the beam-excited HOM power. This means single-cell 400 MHz cavities were chosen for the Z, which will be exchanged for two-cell 400 MHz cavities for the W. At the same time, the booster accelerator will be equipped with 800 MHz five-cell cavities. The number of cryomodules will then increase progressively when moving to the H and ttbar scenarios.  

According to projections, the total power consumption of the FCC-ee ttbar scenario is estimated at 384 MW. Within this budget, 148 MW will be needed for the RF power system and 47.5 MW for the associated cryogenics systems. The RF component is dominated by the synchrotron losses (100 MW), which need to be compensated, and the efficiency of the RF power system to generate this power and transfer it to the beam. The cryogenic budget, on the other hand, is related to the surface resistance of the SRF cavities. The maths is simple enough: decrease the SRF surface resistance by a factor of two – and the power consumption of the cryogenic system falls by a factor of two (which, in turn, would cut the size of the cryogenic plant by half). 

Is such an outcome realistic, though? The current stated R&D goal for 400 MHz FCC-ee cavities is an approximately 30% reduction of surface losses (versus the LHC cavities) together with a doubling of the accelerating gradient. It’s an ambitious goal and, as such, CERN RF engineers are applying the lessons learned from the HIE-ISOLDE project, where the use of seamless cavity substrates made it possible to increase the peak fields in the cavity while lowering surface losses. 

Testing, iteration, continuous improvement

Proof-of-principle tests to date required seamless elliptical cavities, with the CERN workshop able to machine such cavities out of bulk copper pieces, while the technology department’s vacuum group pioneered a method using electroforming. (In the latter, copper is deposited onto an aluminium mandrel, with the aluminium subsequently dissolved to leave behind only the deposited copper layer.) Both approaches were used to make small (scaled) 1.3 GHz cavities, which were then chemically polished and coated using high-power impulse magnetron sputtering (HIPIMS), a specialised method for physical vapour deposition of thin films. 

The figure on page 22 (“Numbers game”) shows the results of the first cold tests as well as the target value for the FCC-ee 400 MHz cavities (the latter scaled, in Q value, to be comparable to the 1.3 GHz cavity results). What’s evident from the data is that the seamless coated cavities have clear potential to reach the FCC-ee performance goal – though it’s worth emphasising that these are simplified test cavities without power couplers and without HOM couplers (plus these cavities are around three times smaller in diameter versus the 400 MHz cavities foreseen for FCC-ee). 

Qualifiers notwithstanding, these results constitute the first significant step forward in thin-film SRF cavity performance since LEP – underpinned by the enhanced HIPIMS coatings, the use of seamless cavity substrates, and the precision control of cavity surface states during chemistry, coating and cold testing. In terms of next steps, CERN’s R&D effort will focus on further improvements in quality factor (inversely proportional to the surface resistance); extending the field reach (so far limited by the experimental set-up, and not by the properties of the test cavities); and the scale-up to much larger cavities. 

The challenges posed by cavity size are twofold: on the one hand, to ensure equal film quality over several square metres of inner surface; on the other, to find a fabrication method that avoids a welding seam at the equator of the cavities. All elliptical cavities built today – whether coated cavities or bulk niobium – are assembled from pre-shaped half-cells. While small 1.3 GHz cavities are straightforward to machine out of a bulk piece of copper, this method quickly becomes uneconomical when considering 400 MHz FCC-type cavities. 

For this reason, CERN has initiated a collaboration with KEK in Japan to explore the potential for seamless cavity fabrication via hydroforming (an advanced die-molding process that relies on highly pressurised fluids to shape metals). While the initial results are encouraging, a lot of prototyping and subsequent coating tests will be needed to develop this technology into a process that can be scaled and industrialised. If successful, the hope is that SRF cavity substrates could ultimately be produced like bodywork pieces for cars – and at a fraction of today’s fabrication costs. 

Another active area of SRF R&D – and the focus of an ongoing CERN collaboration with Fermilab – involves the 800 MHz multicell bulk-niobium cavities foreseen in the FCC-ee baseline scenario. Over the past decade, Fermilab has pioneered advanced surface treatment methods (such as nitrogen doping or infusion) along with various temperature treatments to tailor the surface resistance of 1.3 GHz bulk-niobium cavities for specific applications. 

There’s been significant progress in lowering the surface resistance and the technology has found initial application in the SRF cavities of the Linac Coherent Light Source (LCLS-II) at SLAC in California (with the cavities first being treated and then assembled into cryomodules at Fermilab). In line with the requirements for its Proton Improvement Plan (PIP-II), an ambitious upgrade of the Fermilab accelerator complex, the US laboratory has also started to apply its surface tailoring methods to larger cavities (650 MHz) and, as part of this effort, is keen to include FCC-ee prototypes. 

The outer limits

To push beyond the performance limits of today’s coated or bulk-niobium cavities, CERN, Fermilab and other partner laboratories are evaluating new superconducting materials that operate at higher cryogenic temperatures. CERN, for its part, is making sample tests with thin Nb₃Sn or Vn₃Si layers on copper, while Fermilab scientists are creating a thin layer of Nb₃Sn on pure niobium surfaces. The physics is compelling: if the 800 MHz cavities can operate at 4.2 K instead of 2 K with the same surface resistance, the aggregate cryogenic power consumption will be cut by two-thirds. 

Along another coordinate, unprecedented accelerating gradients can theoretically be achieved by having multi-layered films on top of niobium or copper cavities, with researchers at CEA in France reporting significant progress with the deposition of single atomic layers onto substrates. In short, with the help of targeted R&D, this looks like a promising path to reducing the SRF surface resistance by 50% on average, though success will ultimately depend on the availability of skilled manpower, state-of-the-art materials processing infrastructure as well as precise diagnostics to evaluate SRF performance. 

With this in mind, CERN’s RF group has proposed the construction of a dedicated SRF infrastructure next to the SM18 facility. The new building will provide almost 5000 m² of space for advanced cavity chemistry as well as clean rooms, cryomodule assembly area and materials cleaning facilities. A full integration study and cost estimate is now complete and the project is under consideration for inclusion in CERN’s next Medium-Term Plan (2023–26). 

The future’s bright, it seems, for CERN’s SRF technology programme.

Addendum: In addition to the ongoing collaborative fabrication effort regarding the crab cavities and associated cryomodules, it’s important to highlight the crucial role of the preceding R&D phase. Here, with the financial support of the US LHC Accelerator Research Programme (predecessor of the US HL-LHC Accelerator Upgrade Project), Old Dominion University, JLAB, SLAC and BNL – working together with CERN – designed, developed, prototyped and tested the two crab-cavity types and their HOM damping schemes. Furthermore, we acknowledge support for the R&D effort from UK-STFC and KEK. In the run-up to the FCC R&D effort, and under the US-CERN agreement, JLAB also designed, manufactured and tested the first five-cell 802 MHz bulk niobium cavity, which reached excellent performance with record Q0 value of 3×10¹⁰ at 27 MV/m acceleration gradient at 2 K in this frequency regime.

The post New horizons in SRF: beyond the HL-LHC appeared first on CERN Courier.

Take cosmology and astrophysics. These are fundamental sciences whose aim is nothing more than to better understand the objects within their remit. Telescopes and other instruments point at the universe at large, observing to ever higher precision, farther than ever before, in new, previously inaccessible regimes. The Gaia, JWST and LIGO instruments, which cost between $1–10 billion each, had clear scientific cases: to simply do better science.

Not once in ESA’s list of Gaia science objectives is dark matter or dark energy mentioned. Gaia’s scientific potential is fulfilled not by the promise of new physics discoveries but by improving precision astrometry, uncovering more of the known astrophysical objects and testing further the standard cosmological model. JWST is a success if it makes sharper observations and peers out farther than ever, regardless of whether it discovers new types of exotic phenomena or sees the same objects as before but better. LIGO was not considered a failure for having discovered gravitational-wave signals in agreement with Einstein’s general theory of relativity; nor is the future of gravitational-wave observatories in doubt as a consequence. 

Particle physics is pushing the boundaries of our understanding in the other direction – looking inwards rather than outwards. The discovery of the Higgs boson, like that of gravitational waves, opens an entirely new window for probing our universe. Its agreement with the SM until now does nothing to diminish the need for a future Higgs observatory. Higgs aside, new elementary particle processes are continually being unveiled, from the long-predicted quantum scattering of light by light to complex interactions involving multiple bosons or fermions, most recently in the spectacular observation of four top quarks by ATLAS and CMS.

Gaia, JWST and LIGO had clear scientific cases: to simply do better science

Moreover, unlike cosmology and astrophysics, particle physics can do more than observe. It is an experimental science in the truest sense: set up the initial conditions, repeat the experiment, then analyse what comes out. The ability to directly manipulate the elementary building blocks of our world both complements and works symbiotically with astrophysical and cosmological observations. We need all eyes open on the universe to make progress; blinding one eye will not make the other sharper.

A better name can help

In this spirit, the CERN Future Circular Collider (FCC) is a bold and ambitious proposal for ensuring another thriving century of particle physics. As a multi- generational project, it would be our era’s cathedral to knowledge and wonder about the universe. However, the FCC cannot always remain a future collider if it ever becomes reality. When it comes to be renamed, the CERN International Particle Observatory would be more apt. This better reflects the role of colliders as general-purpose tools to do good science.  

The International Particle Observatory will cost around $10 billion for a high-precision observatory, starting in the 2040s. A high-energy observatory would then follow in the 2070s. Is it worth it? Should we not be more concerned with climate change? Both questions must be put in the context of other areas of government spending and the value of fundamental physics. For example, an Olympic Games funded by a single nation, for a month’s worth of entertainment, costs about $10 billion. The same price tag shared across multiple countries over decades, to uncover fundamental knowledge that stands for all time, is a pittance by comparison. Furthermore, studies have shown that the economic return of investment in CERN outweighs the cost. We get back more than we put in. 

The value of the enterprise itself benefits society in myriad indirect ways, which does not place it at odds with practical issues such as climate change. On the contrary, a new generation of particle-physics experiments stimulating cutting-edge engineering, technology, computing and data analysis, while fostering international collaboration and inspiring popular culture, creates the right conditions for tackling other problems. Particle physics helps humanity prosper in the long run, and has already played an indispensable role in creating our modern world.

Building an International Particle Observatory is a win–win proposition. It pays for itself, contributes to a better society, improves our understanding of the universe by orders of magnitude, and advances our voyage of exploration into the unknown. We just need to shift our narrative to one that emphasises the tremendous range of fundamental science to be done. A better name can help. 

The post Future colliders are particle observatories appeared first on CERN Courier.

Giorgio Brianti, a pillar of CERN throughout his 40-year career, passed away on 6 April at the age of 92. He played a major role in the success of CERN and in particular the LEP project, and his legacy lives on across the whole of the accelerator complex.

Giorgio began his engineering studies at the University of Parma and continued them for three years in Bologna, where he obtained his laurea degree in May 1954. Driven by a taste for research, he learned, thanks to his thesis advisor, that Edoardo Amaldi was setting up an international organization in Geneva called CERN and was invited to meet him in Rome in June 1954. In his autobiography – written for his family and friends – Giorgio describes this meeting as follows: “Edoardo Amaldi received me very warmly and, after various discussions, he said to me: ‘you can go home: you will receive a letter of appointment from Geneva soon’. I thus had the privilege of participating in one of the most important intellectual adventures in Europe, and perhaps the world, which in half a century has made CERN ‘the’ world laboratory for particle physics.”

Giorgio had boundless admiration for John Adams, who had been recruited by Amaldi a year earlier, recounting: “John was only 34 years old, but had a very natural authority. To say that we had a conversation would be an exaggeration, due to my still very hesitant English, but I understood that I was assigned to the magnet group”. After participating in the design of the main bending magnets for the Proton Synchrotron, Giorgio was sent by Adams to Genoa for three years to supervise the construction of 100 magnets made by the leading Italian company in the sector, Ansaldo. Upon his return, he was entrusted with the control group and in 1964 he was appointed head of the synchro-cyclotron (SC) division. After only four years he was asked to create a new division to build a very innovative synchrotron – the Booster – capable of injecting protons into the PS and significantly increasing the intensity of the accelerated current. He described this period as perhaps his happiest from a technical point of view. Adams – who had been appointed Director General of the new CERN-Lab II to construct the 400 GeV Super Proton Synchrotron (SPS) – also entrusted Giorgio with designing and building the experimental areas and their beam lines. The 40th anniversary of their inauguration was celebrated with him in 2018 and the current fixed-target experimental programme profits to this day from his foresight.

Giorgio has left us not only an intellectual but also a spiritual legacy

In January 1979 Giorgio was made head of the SPS division, but only two years later he was called to a more important role, that of technical director, by the newly appointed Director General Herwig Schopper. As Giorgio writes: “The main objectives of the mandate were to build the LEP… which was to be installed in a 27 km circumference tunnel over 100 m deep, and to complete the SPS proton-antiproton program, a very risky enterprise, but whose success in 1982 and 1983 was decisive for the future of CERN”. The enormous technical work required to transform the SPS into a proton-antiproton collider that went on to discover the W and Z bosons took place in parallel with the construction of LEP and the launch of the Large Hadron Collider (LHC) project, which Giorgio personally devoted himself to starting in 1982.

The LHC occupied Giorgio for nearly 15 years, starting from almost nothing. As he writes: “It was initially a quasi-clandestine activity to avoid possible reactions from the delegates of the Member States, who would not have understood an initiative parallel to that of the LEP. The first public appearance of the potential project, which already bore the name Large Hadron Collider, took place at a workshop held in Lausanne and at CERN in the spring of 1984.”

The LHC project received a significant boost from Carlo Rubbia, who became Director General in 1989 and appointed Giorgio as director of future accelerators. While LEP was operating at full capacity during these years, under his leadership new technologies were developed and the first prototypes of high-field superconducting magnets were created. The construction programme for the LHC was preliminarily approved in 1994, under the leadership of Chris Llewellyn Smith. In 1996, one year after Giorgio’s retirement, the final approval was granted. Giorgio continued to work, of course! In particular, in 1996 he agreed to chair the advisory committee of the Proton Ion Medical Machine Study, a working group established within CERN aimed at designing and developing a new synchrotron for medical purposes for the treatment of radio-resistant tumours with carbon ion beams. The first centre was built in Italy, in Pavia, by the Italian Foundation National Centre for Oncological Hadrontherapy (CNAO). He was also an active member of the editorial board of the book “Technology meets Research,” which celebrated 60 years of interaction at CERN between technology and fundamental science.

Giorgio has left us not only an intellectual but also a spiritual legacy. He was a man of great moral rigour, with a strong and contemplative Christian faith, determined to achieve his goals but mindful not to hurt others. He was very attached to his family and friends. His intelligence, kindness, and generosity shone through his eyes and – despite his reserved character – touched the lives of everyone he met.

The post Giorgio Brianti 1930–2023 appeared first on CERN Courier.

Energetic beams of particles are used to explore the fundamental forces of nature, produce known and unknown particles such as the Higgs boson at the LHC, and generate new forms of matter, for example at the future FAIR facility. Photon science also relies on particle beams: electron beams that emit pulses of intense synchrotron light, including soft and hard X-rays, in either circular or linear machines. Such light sources enable time-resolved measurements of biological, chemical and physical structures on the molecular down to the atomic scale, allowing a diverse global community of users to investigate systems ranging from viruses and bacteria to materials science, planetary science, environmental science, nanotechnology and archaeology. Last but not least, particle beams for industry and health support many societal applications ranging from the X-ray inspection of cargo containers to food sterilisation, and from chip manufacturing to cancer therapy. 

This scientific success story has been made possible through a continuous cycle of innovation in the physics and technology of particle accelerators, driven for many decades by exploratory research in nuclear and particle physics. The invention of radio-frequency (RF) technology in the 1920s opened the path to an energy gain of several tens of MeV per metre. Very-high-energy accelerators were constructed with RF technology, entering the GeV and finally the TeV energy scales at the Tevatron and the LHC. New collision schemes were developed, for example the mini “beta squeeze” in the 1970s, advancing luminosity and collision rates by orders of magnitudes. The invention of stochastic cooling at CERN enabled the discovery of the W and Z bosons 40 years ago. 

However, intrinsic technological and conceptual limits mean that the size and cost of RF-based particle accelerators are increasing as researchers seek higher beam energies. Colliders for particle physics have reached a circumference of 27 km at LEP/LHC and close to 100 km for next-generation facilities such as the proposed Future Circular Collider. Machines for photon science, operating in the GeV regime, occupy a footprint of up to several km and the approval of new facilities is becoming limited by physical and financial constraints. As a result, the exponential progress in maximum beam energy that has taken place during the past several decades has started to saturate (see “Levelling off” figure). For photon science, where beam-time on the most powerful facilities is heavily over-subscribed, progress in scientific research and capabilities threatens to become limited by access. It is therefore hoped that the development of innovative and compact accelerator technology will provide a practical path to more research facilities and ultimately to higher beam energies for the same investment. 

At present the most successful new technology relies on the concept of plasma acceleration. Proposed in 1979, this technique promises energy gains up to 100 GeV per metre of acceleration and therefore up to 1000 times higher than is possible in RF accelerators. In essence, the metallic walls of an RF cavity, with their intrinsic field limitations, are replaced by a dynamic and robust plasma structure with very high fields. First, the free electrons in a neutral plasma are used to convert the transverse ponderomotive force of a laser, or the transverse space charge force of a charged particle beam, into a longitudinal accelerating field. While the “light” electrons in the plasma column are expelled from the path of the driving force, the “heavy” plasma ions remain in place. The ions therefore establish a restoring force and re-attract the oscillating plasma electrons. A plasma cavity forms behind the drive pulse in which the main electron beam is placed and accelerated with up to 100 GV per metre. Difficulties in the plasma-acceleration scheme arise from the small scales involved (sub-mm transverse diameter), the required micrometre tolerances and stability. Different concepts include laser-driven plasma wakefield acceleration (LWFA), electron-driven plasma wakefield acceleration (PWFA) and proton-beam-driven plasma wakefield acceleration. Gains in electron energy have reached 8 GeV (BELLA, Berkeley), 42 GeV (FFTB, SLAC) and 2 GeV (AWAKE, CERN) in these three schemes, respectively. 

At the same time, the beam quality of plasma-acceleration schemes has advanced sufficiently to reach the quality required for free-electron lasers (FELs): linac-based facilities that produce extremely brilliant and short pulses of radiation for the study of ultrafast molecular and other processes. There have been several reports of free-electron lasing in plasma-based accelerators in recent years, one relying on LWFA by a team in China and one on PWFA by the EuPRAXIA team in Frascati, Italy. Another publication by a French and German team has recently demonstrated seeding of the FEL process in a LWFA plasma accelerator. 

Scientific and technical progress in plasma accelerators is driven by several dozen groups and a number of major test facilities worldwide, including internationally leading programmes at CERN, STFC, CNRS, DESY, various centres and institutes in the Helmholtz Association, INFN, LBNL, RAL, Shanghai XFEL, SCAPA, SLAC, SPRING-8, Tsinghua University and others. In Europe, the 2020 update of the European strategy for particle physics included plasma accelerators as one of five major themes, and a strategic analysis towards a possible plasma-based collider was published in a 2022 CERN Yellow Report on future accelerator R&D. 

Enter EuPRAXIA

In 2014 researchers in Europe agreed that a combined, coordinated R&D effort should be set up to realise a larger plasma-based accelerator facility that serves as a demonstrator. The project should aim to produce high-quality 5 GeV electron beams via innovative laser- and electron-driven plasma wakefield acceleration, achieving a significant reduction in size and possible savings in cost over state-of-the-art RF accelerators. This project was named the European Plasma Research Accelerator with Excellence in Applications (EuPRAXIA) and it was agreed that it should deliver pulses of X rays, photons, electrons and positrons to users from several disciplines. EuPRAXIA’s beams will mainly serve the fields of structural biology, chemistry, material science, medical imaging, particle-physics detectors and archaeology. It is not a dedicated particle-physics facility but will be an important stepping stone towards any plasma-based collider. 

The EuPRAXIA project started in 2015 with a design study, which was funded under the European Union (EU) Horizon 2020 programme and culminated at the end of 2019 with the publication of the worldwide first conceptual design report for a plasma-accelerator facility. The targets set out in 2014 could all be achieved in the EuPRAXIA conceptual design. In particular, it was shown that sufficiently competitive performances could be reached and that an initial reduction in facility size by a factor of two-to-three is indeed achievable for a 5 GeV plasma-based FEL facility. The published design includes realistic constraints on transfer lines, facility infrastructure, laser-lab space, undulator technologies, user areas and radiation shielding. Several innovative solutions were developed, including the use of magnetic chicanes for high quality, multi-stage plasma accelerators. The EuPRAXIA conceptual design report was submitted to peer review and published in 2020. 

The EuPRAXIA implementation plan proposes a distributed research infrastructure with two construction and user sites and several centres of excellence. The presently foreseen centres, in the Czech Republic, France, Germany, Hungary, Portugal and the UK, will support R&D, prototyping and the construction of machine components for the two user sites. This distributed concept will ensure international competitiveness and leverage existing investments in Europe in an optimal way. Having received official government support from Italy, Portugal, the Czech Republic, Hungary and UK, the consortium applied in 2020 to the European Strategy Forum on Research Infrastructures (ESFRI). The proposed facility for a free-electron laser was then included in the 2021 ESFRI roadmap, which identifies those research facilities of pan-European importance that correspond to the long-term needs of European research communities. EuPRAXIA is the first ever plasma-accelerator project on the ESFRI roadmap and the first accelerator project since the 2016 placement of the High-Luminosity LHC. 

Stepping stones to a user facility 

In 2023 the European plasma-accelerator community received a major impulse for the development of a user-ready plasma-accelerator facility with the funding of several multi-million euro initiatives under the umbrella of the EuPRAXIA project. These are the EuPRAXIA preparatory phase, EuPRAXIA doctoral network and EuPRAXIA advanced photon sources, as well as funding for the construction of one of the EuPRAXIA sites in Frascati, near Rome (see “Frascati future” image). 

The EU, Switzerland and the UK have awarded €3.69 million to the EuPRAXIA preparatory phase, which comprises 34 participating institutes from Italy, the Czech Republic, France, Germany, Greece, Hungary, Israel, Portugal, Spain, Switzerland, the UK, the US and CERN as an international organisation. The new grant will give the consortium a unique chance to prepare the full implementation of EuPRAXIA over the next four years. The project will fund 548 person-months, including additional funding from the UK and Switzerland, and will be supported by an additional 1010 person-months in-kind. The preparatory-phase project will connect research institutions and industry from the above countries plus China, Japan, Poland and Sweden, which signed the EuPRAXIA ESFRI consortium agreement, and define the full implementation of the €569 million EuPRAXIA facility as a new, distributed research infrastructure for Europe. 

Alongside the EuPRAXIA preparatory phase, a new Marie Skłodowska-Curie doctoral network, coordinated by INFN, has also been funded by the EU and the UK. The network, which started in January 2023 and benefits from more than €3.2 million over its four-year duration, will offer 12 high-level fellowships between 10 universities, six research centres and seven industry partners that will carry out an interdisciplinary and cross-sector plasma-accelerator research and training programme. The project’s focus is on scientific and technical innovations, and on boosting the career prospects of its fellows.

EuPRAXIA at Frascati

Italy is supporting the EuPRAXIA advanced photon sources project (EuAPS) with €22 million. This project has been promoted by INFN, CNR and Tor Vergata University of Rome. EuAPS will fulfil some of the scientific goals defined in the EuPRAXIA conceptual design report by building and commissioning a distributed user facility providing users with advanced photon sources; these consist of a plasma-based betatron source delivering soft X-rays, a mid-power, high-repetition-rate laser and a high-power laser. The funding comes in addition to about €120 million for construction of the beam-driven facility and the FEL facility of EuPRAXIA at Frascati. R&D activities for the beam-driven facility are currently being performed at the INFN SPARC_LAB laboratory. 

EuPRAXIA is the first ever plasma-accelerator project on the ESFRI roadmap 

EuPRAXIA will be the user facility of the future for the INFN Frascati National Laboratory. The European site for the second, laser-driven leg of EuPRAXIA will be decided in 2024 as part of the preparatory-phase project. Present candidate sites include ELI-Beamlines in the Czech Republic, the future EPAC facility in the UK and CNR in Italy. With its foreseen electron energy range of 1–5 GeV, the facility will enable applications in diverse domains, for instance, as a compact free-electron laser, compact sources for medical imaging and positron generation, tabletop test beams for particle detectors, and deeply penetrating X-ray and gamma-ray sources for materials testing. The first parts of EuPRAXIA are foreseen to enter into operation in 2028 at Frascati and are designed to be a stepping stone for possible future plasma-based facilities, such as linear colliders at the energy frontier. The project is driven by the excellence, ingenuity and hard work of several hundred physicists, engineers, students and support staff who have worked on EuPRAXIA since 2015, connecting, at present, 54 institutes and industries from 18 countries in Europe, Asia and the US.

The post Europe targets a user facility for plasma acceleration appeared first on CERN Courier.

Following its year-end technical stop (YETS) beginning on 28 November 2022, the LHC is springing back to life to continue Run 3 operations at the energy frontier. The restart process began on 13 February with the beam commissioning of Linac4, which was upgraded during the technical stop to allow a 30% increase in the peak current, to be taken advantage of in future runs. On 3 March the Proton Synchrotron Booster began beam commissioning, followed by the Proton Synchrotron (PS). 

In the early hours of 17 March, the PS sent protons down the transfer lines to the door of the Super Proton Synchrotron (SPS), and the meticulous process of adjusting the thousands of machine parameters began. Following a rigorous beam-based realignment campaign, and a brief interruption to allow transport and metrology experts to move selected magnets, sometimes by only a fraction of a millimetre, SPS operators re-injected the beam and quantified and validated the orbit correction ready for injection into the LHC. Right on schedule, on 28 March the first beams successfully entered the LHC. Thanks to very fast threading, both beams were circulating the same day, even producing first “splash” events in the detectors. As the Courier went to press, the intensity ramp-up was under way. Collisions in the LHC are expected to commence by the end of April, heralding the start of a relatively short but intense physics run that is scheduled to end on 30 October.

Refinements

Among many improvements to the accelerator complex made during the YETS, four modules in the SPS kicker system were upgraded to reduce the amount of heat deposited by the beam, and new instruments were installed in the LHC tunnel. These include the beam gas curtain, which will provide 2D images of the alignment of the beams to make data-taking more precise. Ten years in the making, the device was designed for the high-luminosity upgrade of the LHC (HL-LHC) as part of a collaboration between CERN, Liverpool University, the Cockcroft Institute and GSI.

“It’s a challenging year ahead, with the 2023 run length reduced by 20% for energy cost reasons,” says Rende Steerenberg, head of the operations group. “But we maintain the integrated-luminosity goal of 75 fb^–1 by enhancing the beam performance and maximising beam availability.” 

To cope with the higher luminosities during Run 3, and to prepare for a further luminosity leap at the HL-LHC beginning in 2029, many upgrades to the four main LHC experiments took place during Long Shutdown 2 (LS2) from 2019 to 2022. While the bulk of HL-LHC upgrades for ATLAS and CMS will take place during LS3, beginning in 2026, the ALICE and LHCb detectors underwent significant transformations during LS2. In the final weeks leading to the LHC restart, the LHCb collaboration completed the last element of its Upgrade 1 – the upstream tracker. 

This advanced silicon-strip detector, located at the entrance of the LHCb bending magnet, allows fast determination of track momenta. This speeds up the LHCb trigger by a factor of three, which is vital to operate the newly installed 40 MHz fully software-based trigger. The new tracker will also improve the reconstruction efficiency of long-lived particles that decay after the vertex locator (VELO), and will provide better coverage overall, especially in the very forward regions. It is composed of 968 silicon-hybrid modules arranged in four vertical planes to handle the varying occupancy over the detector acceptance. A dedicated front-end ASIC, the “SALT chip”, provides pulse shaping with fast baseline restoration and digi­tisation, while nearby detector electronics implement the transformation to optical signals that are transmitted to the remote data-acquisition system in LHCb’s new data centre. Institutes from the US, Italy, Switzerland, Poland and China were involved in designing, building and testing the upstream tracker. Assembly began in 2021 and intensive work took place underground throughout the recent YETS, so the device installation was successfully completed by cavern closure on 27 March.

Under pressure

However, earlier in the year, there was an incident that affected another LHCb subdetector, the VELO. This occurred on 10 January, when there was a loss of control of the LHC primary vacuum system at the interface with the VELO. At the time, the primary and secondary vacuum volumes were filled with neon as the installation of the upstream tracker was taking place. A failure in one of the relays in the overpressure safety system not only prevented the safety system from triggering at the appropriate time, but also led to an issue with the power supply that supports some of the machine instrumentation, causing the pressure balancing system to mistakenly pump on the primary volume. The subsequent pressure build-up went beyond specification limits and led to a plastic deformation of the mechanical interface – an ultrathin aluminium shield called the “RF box” – between the LHC and detector volumes. The RF box is mechanically linked to the VELO and a change in its shape affects the degree to which the VELO can be moved and centred around the colliding beams.

To minimise any risk of impact on the other LHC experiments, the LHCb collaboration will wait until this year’s YETS to replace the RF box. In the meantime, the collaboration has been developing ways to mitigate the impact on data-taking, explains LHCb spokesperson Chris Parkes of the University of Manchester: “Initially we were very concerned that the VELO could have been damaged, but fortunately this is not the case. After much careful recovery work, we will be able to operate the system in 2023, and after the RF box is replaced, we will be back to full performance.”

The post Back to life: LHC Run 3 recommences appeared first on CERN Courier.

The era of high-temperature superconductivity started in 1986 with the discovery, by IBM researchers Georg Bednorz and Alex Muller, of superconductivity in a lanthanum barium copper oxide. This discovery was revolutionary: not only did the new, brittle superconducting compound belong to the family of ceramic oxides, which are generally insulators, but it had the highest critical temperature ever recorded (up to 35 K, compared with about 18 K in conventional superconductors). In the following years, scientists discovered other cuprate superconductors (bismuth–strontium–copper oxide and yttrium–barium–copper oxide) and achieved superconductivity at temperatures above 77 K, the boiling point of liquid nitrogen (see “Heat is rising” figure). The possibility of operating superconducting systems with inexpensive, abundant and inert liquid nitrogen generated tremendous enthusiasm in the superconducting community. 

Several applications of high-temperature superconducting materials with a potentially high impact on society were studied. Among them, superconducting transmission lines were identified as an innovative and effective solution for bulk power transmission. The unique advantages of superconducting transmission are high capacity, very compact volume and low losses. This enables the sustainable transfer of up to tens of GW of power at low and medium voltages in narrow channels, together with energy savings. Demonstrators have been built worldwide in conjunction with industry and utility companies, some of which have successfully operated in national electricity grids. However, widespread adoption of the technology has been hindered by the cost of cuprate superconductors. 

In particle physics, superconducting magnets allow high-energy beams to circulate in colliders and provide stronger fields for detectors to be able to handle higher collision energies. The LHC is the largest superconducting machine ever built, and the first to also employ high-temperature superconductors at scale. Realising its high-luminosity upgrade and possible future colliders is driving the use of next-generation superconducting materials, with applications stretching far beyond fundamental research.

High-temperature superconductivity (HTS) was discovered at the time when the conceptual study for the LHC was ongoing. While the new materials were still in a development phase, the potential of HTS for use in electrical transmission was immediately recognised. The powering of the LHC magnets (which are based on the conventional superconductor niobium titanium, cooled by superfluid helium) requires the transfer of about 3.4 MA of current, generated at room temperature, in and out of the cryogenic environment. This is done via devices called current leads, of which more than 3000 units are installed at different underground locations around the LHC’s circumference. The conventional current–lead design, based on vapour-cooled metallic conductors, imposes a lower limit (about 1.1 W/kA) on the heat in-leak into the liquid helium. The adoption of the HTS BSCCO 2223 (bismuth–strontium–calcium copper oxide ceramic) tape – operated in the LHC current leads in the temperature range 4.5 to 50 K – enabled thermal conduction and ohmic dissipation to be disentangled. Successful multi-disciplinary R&D followed by prototyping at CERN and then industrialisation, with series production of the approximately 1100 LHC HTS current leads starting in 2004, resulted in both capital and operational savings (avoiding one extra cryoplant and an economy of about 5000 l/h of liquid helium). It also encouraged wider adoption of BSCCO 2223 current–lead technology, for instance in the magnet circuits for the ITER tokamak, which benefit via a collaboration agreement with CERN on the development and design of HTS current leads.

MgB₂ links at the HL-LHC 

The discovery of superconductivity in magnesium diboride (MgB₂) in 2001 generated new enthusiasm for HTS applications. This material, classified as medium-temperature superconductor, has remarkable features: it has a critical temperature (39 K) some 30 K higher than that of niobium titanium, a high current density (to date in low and medium magnetic fields) and, crucially, it can be industrially produced as round multi-filamentary wire in long (km) lengths. These characteristics, along with a cost that is intrinsically lower than other available HTS materials, make it a promising candidate for electrical applications.

At the LHC the current leads are located in the eight straight sections. For the high-luminosity upgrade of the LHC (HL-LHC), scheduled to be operational in 2029, the decision was taken to locate the power converters in new, radiation-free underground technical galleries above the LHC tunnel. The distance between the power converters and the HL-LHC magnets spans about 100 m and includes a vertical path via an 8 m shaft connecting the technical galleries and the LHC tunnel. The large current to be transferred across such distance, the need for compactness, and the search for energy efficiency and potential savings led to the selection of HTS transmission as the enabling technology.

The electrical connection, at cryogenic temperature, between the HL-LHC current leads and the magnets is performed via superconducting links based on MgB₂ technology. MgB₂ wire is assembled in cables with different layouts to transfer currents ranging from 0.6 kA to 18 kA. The individual cables are then arranged in a compact assembly that constitutes the final cable feeding the magnet circuits of either the HL-LHC inner triplets (a series of quadrupole magnets that provides the final focusing of the proton beams before collision in ATLAS and CMS) or the HL-LHC matching sections (which match the optics in the arcs to those at the entrance of the final-focus quadrupoles), and the final cable is incorporated in a flexible cryostat with an external diameter of up to 220 mm. The eight HL-LHC superconducting links are about 100 m long and transfer currents of about 120 kA for the triplets and 50 kA for the matching sections at temperatures up to 25 K, with cryogenic cooling performed with helium gas.

The R&D programme for the HL-LHC superconducting links started in around 2010 with the evaluation of the MgB₂ conductor and the development, with industry, of a round wire with mechanical properties enabling cabling after reaction. Brittle superconductors, such as Nb₃Sn – used in the HL-LHC quadrupoles and also under study for future high-field magnets – need to be reacted into the superconducting phase via heat treatments, at high temperatures, performed after their assembly in the final configuration. In other words, those conductors are not superconducting until cabling and winding have been performed. When the R&D programme was initiated, industrial MgB₂ conductor existed in the form of multi-filamentary tape, which was successfully used by ASG Superconductors in industrial open MRI systems for transporting currents of a few hundred amperes. The requirement for the HL-LHC to transfer current to multiple circuits for a total of up to 120 kA in a compact configuration, with multiple twisting and transposition steps necessary to provide uniform current distribution in both the wires and cables, called for the development of an optimised multi-filamentary round wire. 

Carried out in conjunction with ASG Superconductors, this development led to the introduction of thin niobium barriers around the MgB₂ superconducting filaments to separate MgB₂ from the surrounding nickel and avoid the formation of brittle MgB₂–Ni reaction layers that compromise electro-mechanical performance; the adoption of higher purity boron powder to increase current capability; the optimisation in the fraction of Monel (a nickel-copper alloy used as the main constituent of the wire) in the 1 mm-diameter wire to improve mechanical properties; the minimisation of filament size (about 55 µm) and twist pitch (about 100 mm) for the benefit of electro-mechanical properties; the addition of a copper stabiliser around the Monel matrix; and the coating of tin–silver onto the copper to ensure the surface quality of the wire and a controlled electrical resistance among wires (inter-strand resistance) when assembled into cables. After successive implementation and in-depth experimental validation of all improvements, a robust 1 mm-diameter MgB₂ wire with required electro-mechanical characteristics was produced. 

The next step was to manufacture long unit lengths of MgB₂ wire via larger billets (the assembled composite rods that are then extruded and drawn down in a long wire). The target unit length of several kilometres was reached in 2018 when series procurement of the wire was launched. In parallel, different cable layouts were developed and validated at CERN. This included round MgB₂ cables in a co-axial configuration rated for 3 kA and for 18 kA at 25 K (see “Complex cabling” figure). While the prototypes made at CERN were 20 to 30 m long, the cable layout incorporated, from the outset, characteristics to enable production via industrial cabling machines of the type used for conventional cables. Splice techniques as well as detection and protection aspects were addressed in parallel with wire and cable development. Both technologies are strongly dependent on the characteristics of the superconductor, and are of key importance for the reliability of the final system. 

The first qualification at 24 K of a 20 kA MgB₂ cable produced at CERN, comprising two 20 m lengths connected together, took place in 2014. This followed the qualification at CERN of short-model cables and other technological aspects, as well as the construction of a dedicated test station enabling the measurement of long cables operated at higher temperatures, in a forced flow of helium gas. The cables were then industrially produced at TRATOS Cavi via a contract with ICAS, in a close and fruitful collaboration that enabled – while operating heavy industrial equipment – the requirements identified during the R&D phase. The complexity of the final cables required a multi-step process that used different cabling, braiding and electrically insulating lines, and the implementation of a corresponding quality-assurance programme. The first industrial cables, which were 60 m long, were successfully qualified at CERN in 2018. Final prototype cables of the type needed for the HL-LHC (for both the triplets and matching sections) were validated at CERN in 2020, when series production of the final cables was launched. As of today, the full series of about 1450 km of MgB₂ wire – the first large-scale production of this material – and five of the eight final MgB₂ cables needed for the HL-LHC have been produced.

The use of hydrogen can diversify energy sources as it significantly reduces greenhouse-gas emissions and environmental pollution during energy conversion

Superconducting wire and cables are the core of a superconducting system, but the system itself requires a global optimisation, which is achieved via an integrated design. Following this approach, the challenge was to investigate and develop, in industry, long and flexible cryostats for the superconducting links with enhanced cryogenic performance. The goal was to achieve a low static heat load (< 1.5 W/m) into the cryogenic volume of the superconducting cables while adopting a design – a two-wall cryostat without intermediate thermal screen – that simplifies the cooling of the system, improves the mechanical flexibility of the links and eases handling during transport and installation. This development, which ran in parallel with the wire and cable activities, led to the desired results and, after an extensive test campaign at CERN, the developed technology was adopted. Series production of these cryostats is taking place at Cryoworld in the Netherlands.

The optimised system minimises the cryogenic cost for the cooling such that a superconducting link transfers – from the tunnel to the technical galleries – just enough helium gas to cool the resistive section of the current leads and brings it to the temperature (about 20 K) for which the leads are optimised. In other words, the superconducting link does not add cryogenic cost to the refrigeration of the system. The links, which are rated for currents up to 120 kA, are sufficiently flexible to be transported, as for conventional power cables, on drums about 4 m in diameter and can be manually pulled, without major tooling, during installation (see “kA currents” image). The challenge of dealing with the thermal contraction of the superconducting links, which shrink by about 0.5 m when cooled down to cryogenic temperature, was also addressed. An innovative solution, which takes advantage of bends and is compatible with the fixed position of the current lead cryostat, was validated with prototype tests. 

Novel HTS leads

Whereas MgB₂ cables transfer high DC currents from the 4.5 K liquid helium environment in the LHC tunnel to about 20 K in the HL-LHC new underground galleries, a different superconducting material is required to transfer the current from 20 to 50 K, where the resistive part of the current leads makes the bridge to room temperature. To cope with the system requirements, novel HTS current leads based on REBCO (rare-earth barium copper oxide) HTS superconducting tape – a material still in a development phase at the time of the LHC study – have been conceived, constructed and qualified to perform this task (see “Bridging the gap” image). Compact, round REBCO cables ensure, across a short (few-metre-long) length, the electrical transfer from the MgB₂ to 50 K, after which the resistive part of the current leads finally brings the current to room temperature. In view of the complexity of dealing with the REBCO conductor, the corresponding R&D was done at CERN, where a complex dedicated cabling machine was also constructed. 

While REBCO tape is procured from industry, the challenges encountered during the development of the cables were many. Specific issues associated with the tape conductor, for example electrical resistance internal to the tape and the dependence of electrical properties on temperature and cycles applied during soldering, were identified and solved with the tape manufacturers. A conservative approach imposing zero critical current degradation of the tape after cabling was implemented. The lessons learnt from this development are also instrumental for future projects employing REBCO conductors, including the development of high-field REBCO coils for future accelerator magnets. 

The series components of the HL-LHC cold-powering systems (superconducting links with corresponding terminations) are now in production, with the aim to have all systems available and qualified in 2025 for installation in the LHC underground areas during the following years. Series production and industrialisation were preceded by the completion of R&D and technological validations at CERN. Important milestones have been the test of a sub-scale 18 kA superconducting link connected to a pair of novel REBCO current leads in 2019, and the test of full-cross section, 60 m-long superconducting lines of the type needed for the LHC triplets and for the matching sections, both in 2020. 

The complex terminations of the superconducting links involve two types of cryostat that contain, at the 20 K side, the HTS current leads and the splices between REBCO and MgB₂ cables and, at the 4.2 K side, the splices between the niobium titanium and the MgB₂ cables. A specific development in the design was to increase compactness and enable the connection of the cryostat with the current leads to the superconducting link at the surface, prior to installation in the HL-LHC underground areas (see “End of the line” figure). The series production of the two cryostat terminations is taking place via collaboration agreements with the University of Southampton and Uppsala University.     

The displacement of the current leads via the adoption of superconducting links brings a number of advantages. These include freeing precious space in the main collider ring, which becomes available for other accelerator equipment, and the ability to locate powering equipment and associated electronics in radiation-free areas. The latter relaxes radiation-hardness requirements for the hardware and eases access for personnel to carry out the various interventions required during accelerator operations. 

Cooling with low-density helium gas also makes electrical transfer across long vertical distances feasible. The ability to transfer high currents from underground tunnels to surface buildings – as initially studied for the HL-LHC – is therefore of interest for future machines, such as the proposed Future Circular Collider at CERN. Flexible superconducting links can also be applied to “push–pull” arrangements of detectors at linear colliders such as the proposed CLIC and ILC, where the adoption of flexible powering lines can simplify and reduce the time for the exchange of experiments sharing the same interaction region.

An enabling technology

Going beyond fundamental research in physics, superconductivity is an enabling technology for the transfer of GWs of power across long distances. The main benefits, in addition to incomparably higher power transmission, are small size, low total electrical losses, minimised environmental impact and more sustainable transmission. HTS offers the possibility of replacing resistive high-voltage overhead lines, operated across thousands of kilometres at voltages reaching about 1000 kV, with lower voltage lines, laid underground with reduced footprints.

Long-distance power transmission using hydrogen- cooled MgB₂ superconducting links, potentially associated with renewable energy sources, is identified as one of the leading ways towards a future sustainable energy system. Since hydrogen is liquid at 20 K (the temperature at which MgB₂ is superconducting), large amounts can be stored and used as a coolant for superconducting lines, acting at the same time as the energy vector and cryogen. In this direction, CERN participated – at a very early stage of the HL-LHC superconducting links development – in a project launched by Carlo Rubbia as scientific director of the Institute for Advanced Sustainability Studies (IASS) in Potsdam. Around 10 years ago, CERN and IASS joint research culminated in the record demonstration of the first 20 kA MgB₂ transmission line operated at liquid hydrogen temperature. This activity continued with a European initiative called BestPaths, which demonstrated a monopole MgB₂ cable system operated in helium gas at 20 K. This was qualified in industry for 320 kV operation and at 10 kA at CERN, proving 3.2 GW power transmission capability. This initiative involved European industry and France’s transmission system operator. In Italy, the INFN has recently launched a project called IRIS based on similar technology (see CERN Courier January/February 2023 p9).

In addition to transferring power across long distances with low losses and minimal environmental impact, the development of high-performance, low-cost, sustainable and environmentally friendly energy storage and production systems is a key challenge for society. The use of hydrogen can diversify energy sources as it significantly reduces greenhouse-gas emissions and environmental pollution during energy conversion. In aviation, alternative-propulsion systems are studied to reduce CO₂ emission and move toward zero-emission flights. Scaling up electric propulsion to larger aircraft is a major challenge. Superconducting technologies are a promising solution as they can increase power density in the propulsion chain while significantly lowering the mass of the electrical distribution system. In this context, a collaboration agreement has recently been launched between CERN and Airbus UpNext. The construction of a demonstrator of superconducting distribution in aircraft called SCALE (Super-Conductor for Aviation with Low Emissions), which uses the HL-LHC superconducting link technology, was recently launched at CERN. 

CERN’s developed experience in superconducting-link technology is also of interest to large data centres, with a collaboration agreement between CERN and Meta under discussion. The possibility of locating energy equipment remotely from servers, of transferring efficiently large power in a compact volume, and of meeting sustainability goals by reducing carbon footprints are motivating a global re-evaluation of conventional systems in light of the potential of superconducting transmission.

Such applications demonstrate the virtuous circle between fundamental and applied research. The requirements of fundamental exploration in particle physics research have led to the development of increasingly powerful and sophisticated accelerators. In this endeavour, scientists and engineers engage in developments initially conceived to address specific challenges. This often requires a multi-disciplinary approach and collaboration with industry to transform prototypes into mature technology ready for large-scale application. Accelerator technology is a key driver of innovation that may also have a wider impact on society. The superconducting-link system for the HL-LHC project is a shining example.

The post New superconducting technologies for the HL-LHC and beyond appeared first on CERN Courier.

The ep/eA programme finds itself at a crossroad between nuclear and particle physics, with synergies with astroparticle physics. It has the potential to empower the High-Luminosity LHC (HL-LHC) physics programme in a unique way, and allows for a deeper exploration of the electroweak and strong sectors of the Standard Model beyond what can be achieved with proton–proton collisions alone. In many cases, adding LHeC to HL-LHC data can significantly improve the precision of Higgs-boson measurements – similar to the improvements expected when moving from the LHC to HL-LHC.

The innovative spirit of the ep/eA community was demonstrated during the workshop “Electrons for the LHC – LHeC/FCCeh and PERLE” held at IJCLab from 26 to 28 October. As the ep/eA community moves from the former HERA facility and from the Electron-Ion Collider, currently under construction at Brookhaven, to higher energies at LHeC and FCC-eh, the threshold will be reached to study electroweak, top and Higgs physics in deep-inelastic scattering (DIS) processes for the first time. In addition, these programmes enable the exploration of the low Bjorken-x frontier orders of magnitude beyond current DIS results. At this stage, it is unclear what physics will be unlocked if hadronic matter is broken into even smaller pieces. In recent years, particle physicists have learned that the ultimate precision for Higgs-boson physics lies in the complementarity of e⁺e^–, pp and ep collisions, as embedded in the FCC programme, for example. Exploiting this complementarity is key to exploring new territories via the Higgs and dark sectors, as well as zooming in on potential anomalies in our data.

The October workshop underlined the advantage of a joint ep/pp/eA/AA/pA interaction experiment, and the need to further document its added scientific value. For example, a precision of 1 MeV on the W-boson mass could be within reach. In short, the ep data allows constraints to be placed on the most important systematic uncertainty when measuring the W-boson mass with pp data.

Reduced power 

Participants also addressed how to reduce the power consumption of LHeC and FCC-eh. PERLE, an expanding international collaboration revolving around a multi-turn demonstrator facility being pursued at IJCLab in Orsay for energy recovery linacs (ERLs) at high beam currents, is ready to become Europe’s leading centre for developing and testing sustainable accelerating systems.  

At this stage, it is unclear what physics will be unlocked if hadronic matter is broken into even smaller pieces

As demonstrated at the workshop, with additional R&D on ERLs and ep colliders we might be able to further reduce the power consumption of the LHeC (and FCC-eh) to as low as 50 MW. These values are to be compared with the GW power consumption if there was no energy recovery and therefore provide a power-economic avenue to extend the Higgs precision frontier beyond the HL-LHC. ERLs are not uniquely applicable to eA colliders, but have been discussed for future linear and circular e⁺e^– colliders too. With PERLE and other sustainable accelerating systems, the ep/eA programme has the ambition to deliver a demonstration of ERL technology at high beam current, potentially towards options for an ERL-based Higgs factory.

Workshop participants are engaged to further develop an ep/eA programme with the ability to significantly enrich this overall strategy with a view to finding cracks in the Standard Model and/or finding new phenomena that further our understanding of nature at the smallest and largest scales.

The post Innovation on show for future ep/eA colliders appeared first on CERN Courier.

The CERN Linear Electron Accelerator for Research (CLEAR) is a prominent example. Launched in August 2017 (CERN Courier November 2017 p8), CLEAR is a user facility developed from the former CTF3 project which existed to test technologies for the Compact Linear Collider (CLIC) – a proposed e⁺e^– collider at CERN that would follow the LHC. During the past five years, beams with a wide range of parameters have been provided to groups from more than 30 institutions across more than 10 nations.

CLEAR was proposed as a response to the low availability of test-beam facilities in Europe. In particular, there was very little time available to users on accelerators with electron beams with an energy of a few hundred MeV, as these tend to be used in dedicated X-ray light-source and other specialist facilities. CLEAR therefore serves as a unique facility to perform R&D towards a wide range of accelerator-based technologies in this energy range. Independent of CERN’s other accelerator installations, CLEAR has been able to provide beams for around 35 weeks per year since 2018, as well as during long shutdowns, and even managing successful operation during the COVID-19 pandemic. 

Flexible physics

As a relatively small facility, CLEAR operates in a flexible fashion. Operators can vary the range of beams available with relative ease by tailoring many different parameters, such as the bunch charge, length and energy, for each user. There is regular weekly access to the machine and, thanks to the low levels of radioactivity, it is possible to gain access to the facility several times per day to adjust experimental setups if needed. Along with CLEAR’s location at the heart of CERN, the facility has attracted an eager stream of users from day one.

CLEAR has attracted an eager stream of users from day one

Among the first was a team from the European Space Agency working in collaboration with the Radiation to Electronics (R2E) group at CERN. The users irradiated electronic components for the JUICE (Jupiter Icy Moons Explorer) mission with 200 MeV electron beams. Their experiments demonstrated that high-energy electrons trapped in the strong magnetic fields around Jupiter could induce faults, so-called single event upsets, in the craft’s electronics, leading to the development and validation of components with the appropriate radiation-hardness. The initial experiment has been built upon by the R2E group to investigate the effect of electron beams on electronics.

As the daughter of CTF3, CLEAR has continued to be used to test the key technological developments necessary for CLIC. There are two prototype CLIC accelerating structures in the facility’s beamline. Originally installed to test CLIC’s unique two-beam acceleration scheme, the structures have been used to study short-range “wakefield kicks” that can deflect the beam away from the planned path and reduce the luminosity of a linear collider. Additionally, prototypes of the high-resolution cavity beam position monitors, which are vital to measure and control the CLIC beam, have been tested, showing promising initial results.

One of the main activities at CLEAR concerns the development and testing of beam instrumentation. Here, the flexibility and the large beam-parameter range provided by the facility, together with easy access, especially in its dedicated in-air test station, have proven to be very effective. CLEAR covers all phases of the development of novel beam diagnostics devices, from the initial exploration of a concept or physical mechanism to the first prototyping and to the testing of the final instrument adapted for use in an operational accelerator. Examples are beam-loss monitors based on optical fibres, and beam-position and bunch-length monitors based on Cherenkov diffraction radiation under development by the beam instrumentation group at CERN.

Advanced accelerator R&D

There is a strong collaboration between CLEAR and the Advanced Wakefield Experiment (AWAKE), a facility at CERN used to investigate proton-driven plasma wakefield acceleration. In this scheme, which promises higher acceleration gradients than conventional radio-frequency accelerator technology and thus more compact accelerators, charged particles such as electrons are accelerated by forcing them to “surf” atop a longitudinal plasma wave that contains regions of positive and negative charges. Several beam diagnostics for the AWAKE beamline were first tested and optimised at CLEAR. A second phase of the AWAKE project, presently being commissioned for operation in 2026, requires a new source of electron beams to provide shorter, higher quality beams. Before its final installation in AWAKE, it is proposed to use this source to increase the range of beam parameters available at CLEAR.

Further research into compact, plasma-based accelerators has been undertaken at CLEAR thanks to the installation of an active plasma lens on the beamline. Such lenses use gases ionised by very high electric currents to provide focusing for beams many orders of magnitude stronger than can be achieved with conventional magnets. Previous work on active plasma lenses had shown that the focusing force was nonlinear and reduced the beam quality. However, experiments performed at CLEAR showed, for the first time, that by simply swapping the commonly used helium gas for a heavier gas like argon, a linear magnetic field could be produced and focusing could be achieved without reducing the beam quality (CERN Courier December 2018 p8). 

Plasma acceleration is not the only novel accelerator technology that has been studied at CLEAR over the past five years. The significant potential of using accelerators to produce intense beams of radiation in the THz frequency range has also been demonstrated. Such light, on the boundary between microwaves and infrared, is difficult to produce, but has a variety of different uses ranging from imaging and security scanning to the control of materials at the quantum level. Compact linear accelerator-based sources of THz light could potentially be advantageous to other sources as they tend to produce significantly higher photon fluxes. By using long trains of ultrashort, sub-ps bunches, it was shown at CLEAR that THz radiation can be generated through coherent transition radiation in thin metal foils, through coherent Cherenkov radiation, and through coherent “Smith–Purcell” radiation in periodic gratings. The peak power emitted in experiments at CLEAR was around 0.1 MW. However, simulations have shown that with relatively minor reductions in the length of the electron bunches it will be possible to generate a peak power of more than 100 MW. 

FLASH forward

Advances in high-gradient accelerator technology for projects like CLIC (CERN Courier April 2018 p32) have led to a surge of interest in using electron beams with energies between 50–250 MeV to perform radiotherapy, which is one of the key tools used in the treatment of cancer. The use of so-called very-high energy electron (VHEE) beams could provide advantages over existing treatment types. Of particular interest is using VHEE beams to perform radiotherapy at ultra-high dose rates, which could potentially generate the so-called FLASH effect in patients. Here, tumour cells are killed while sparing the surrounding healthy tissues, with the potential to significantly improve treatment outcomes. 

So far, CLEAR has been the only facility in the world studying VHEE radiotherapy and FLASH with 200 MeV electron beams. As such, there has been a large increase in beam-time requests in this field. Initial tests performed by researchers from the University of Manchester demonstrated that, unlike other types of radiotherapy beams, VHEE beams are relatively insensitive to inhomogeneities in tissue that typically result in less targeted treatment. The team, along with another from the University of Strathclyde, also looked at how focused VHEE beams could be used to further target doses inside a patient by mimicking the Bragg peak seen in proton radiotherapy. Experiments with the University Hospital of Lausanne to try to demonstrate whether the FLASH effect can be induced with VHEE beams are ongoing (CERN Courier January/February 2023 p8). 

Even if the FLASH effect can be produced in the lab, there are issues that need to be overcome to bring it to the clinic. Chief among them is the development of novel dosimetric methods. As CLEAR and other facilities have shown, conventional real-time dosimetric methods do not work at ultra-high dose rates. Ionisation chambers, the main pillar of conventional radiotherapy dosimetry, were shown to have very nonlinear behaviour at such dose rates, and recombination times that were too long. Due to this, CLEAR has been involved in the testing of modified ionisation chambers as well as other more innovative detector technologies from the world of particle physics for use in a future FLASH facility. 

High impact 

As well as being a test-bed for new technologies and experiments, CLEAR has provided an excellent training infrastructure for the next generation of physicists and engineers. Numerous masters and doctoral students have spent a large portion of their time performing experiments at CLEAR either as one-time users or long-term collaborators. Additionally, CLEAR is used for practical accelerator training for the Joint Universities Accelerator School.

Numerous masters and doctoral students have spent time performing experiments at CLEAR

As in all aspects of life, the COVID-19 pandemic placed significant strain on the facility. The planned beam schedule for 2020 and beyond had to be scrapped as beam operation was halted during the first lockdown and external users were barred from travelling. However, through the hard work of the team, CLEAR was able to recover and run at almost full capacity within weeks. Several internal CERN users, many of whom were unable to travel to external facilities, were able to use CLEAR during this period to continue their research. Furthermore, CLEAR was involved in CERN’s own response to the pandemic by undertaking sterilisation tests of personal protective equipment.

Test-beam facilities such as CLEAR are vital for developing future physics technology, and the impact that such a small facility has been able to produce in just a few years is impressive. A variety of different experiments from several different fields of research have been performed, with many more that are not mentioned in this article. Unfortunately for the world of high-energy physics, the aforementioned shortage of accelerator test facilities has not gone away. CLEAR will continue to play its role in helping provide test beams, with operations due to continue until at least 2025 and perhaps long after. There is an exciting physics programme lined up for the next few years, featuring many experiments similar to those that have already been performed but also many that are new, to ensure that accelerator technology continues to benefit both science and society.

The post CLEAR highlights and goals appeared first on CERN Courier.

Laser-driven plasma-wakefield acceleration, which is under study at DESY, SLAC and several other labs worldwide, promises to significantly reduce the size of particle accelerators. The idea is to use a high-power laser to create a plasma in a gas, in which charge displacements generate electric fields of the order 100 GV/m. Such fields can accelerate electron bunches to highly relativistic energies over short distances, outperforming conventional radio-frequency technologies by orders of magnitude. The AWAKE experiment at CERN, meanwhile, is a unique facility for the investigation of proton-driven plasma acceleration, which could enable even higher energies to be reached. Turning the concept of wakefield acceleration into a practical device, on the other hand, is a major challenge. 

Turning the concept of wakefield acceleration into a practical device is a major challenge

In order to understand and thus improve the process of laser-plasma acceleration, which lasts for a period of femtoseconds to picoseconds, it is essential to observe as precisely as possible how the properties of the accelerated particles change in the plasma. Publishing their results in December, a team led by DESY’s Simon Bohlen and Kristjan Põder tracked the evolution of the electron beam energy inside a laser-plasma accelerator with high spatial resolution. The feat was performed within a project called PLASMED X, which aims to develop a compact, narrowband and tunable X-ray source for medical imaging. 

The team began by splitting the laser beam into two parts: one was used for electron acceleration, while the other was superimposed so that the light could be scattered by the electrons. Using an X-ray detector to measure the energy of Thomson-scattered photons at 20 points over a 400 μm section of the plasma, the team was able to reconstruct the energy evolution of the electrons over most of the accelerator length without disturbing either the electron beam or the acceleration process itself. 

“We were able to show in our measurements that the acceleration gradient can change significantly over very short distances,” says Bohlen. “With the new measurement method, we now have direct insight into a plasma acceleration process and can thus investigate the direct influence of different laser parameters or geometries of plasma cells on the acceleration process.”

The post Plasma acceleration under the microscope appeared first on CERN Courier.

In the first chapter, I particularly liked the way the author transitions from the Vlasov equation, a very powerful technique for studying beam–beam effects, towards the Fokker–Planck equation describing the statistical interaction of charged particles inside an accelerator. Chao pedagogically introduces the potential-well distortion, which is complemented by illustrations. The discussion on wakefield acceleration, taking readers deeper into the subject and extending it both for proton and electron beams, is timely. Extending the Fokker–Planck equation to 2D and 3D systems is particularly advanced but at the same time important. The author discusses the practical applications of the transient beam distribution in simple steps and introduces the higher order moments later. The proposed exercises, for some of which solutions are provided, are practical as well.

In chapter two, the concept of symplecticity, the conservation of phase space (a subject that causes much confusion), is discussed with concrete examples. Naming issues are meticulously explained, such as using the term short-magnet rather than thin-lens approximation in formula 2.6. Symplectic models for quadrupole magnets are introduced and the following discussion is extremely useful for students and accelerator physicists who will use symplectic codes such as MAD-X and who would like to understand the mathematical framework of their operation. This nicely conjuncts with the next chapter and the book offers useful insights to how these codes operate. In the discussion about third-order integration, Chao makes occasional mental leaps, which could be mitigated with an additional sentence. Although the discussion on higher order and canonical integrators is rather specialised, it is still very useful.

The author introduces the extremely convenient and broadly used truncated power series algebra (TPSA) technique, used to obtain maps, in chapter three. Chao explains in a simple manner the transition from the pre-TPSA algorithms (such as TRANSPORT or COSY) to symplectic algorithms such as MAD-X or PTC, as well as the reason behind this evolution. The clear “drawbacks” discussion is very useful in this regard. 

The transition to Lie algebra in chapter four is masterful and pedagogical. Lie algebras, which can be an advanced topic and come with many formulas, are the main focus in this section of the book. In particular, the non-linearity of the drift space, which is absent of fields, should catch the reader’s attention. This is followed by specialised applications for expert readers only. One of this chapter’s highlights is the derivation of the sextupole pairing, which is complemented by that of Taylor maps up to the second order and its Lie algebra, although it would be better if the “Our plan” section was placed at the beginning of the chapter.

Chapter five covers proton-spin dynamics. Spinor formulas and the Froissart–Stora equation for the polarisation change are developed and explained. The Siberian snake technique remains one of the most well-known to retain beam polarisation, which the author discusses in detail. This links elegantly to chapter six, which introduces the reader to electron-spin dynamics where synchrotron radiation is the dominant effect and therefore constitutes a completely different research area. Chao focuses on the differences between the quantum and classical approach to synchrotron radiation, a phenomenon that cannot be ignored in high-brightness machines. Analogies between protons and electrons are then very well summarised in the recap figure 6.3. Section 6.5 is important for storage rings and leads smoothly to the Derbenev–Kondratenko formula and its applications.

Echoes

Chapter seven looks at echoes, a key technique when measuring diffusion in an accelerator, where the author introduces the reader to the generality of the term and the concept of echoes in accelerator physics. Transverse echoes (with and without diffusion) are quite analytical and the figures are didactic.

The book concludes with a very complete, concise and detailed chapter about beam–beam effects, which acts as an introduction to collider–accelerator physics for coherent- and incoherent-effects studies. Although synchro-betatron couplings causing resonant instabilities are advanced topics, they are often seen in practice when operating the machines, and the book offers the theoretical background for a deeper understanding of these effects.

Special Topics in Accelerator Physics is well written and develops the advanced subjects in a comprehensive, complete and pedagogical way.

The post A clear guide for accelerator physicists appeared first on CERN Courier.

The high-luminosity phase of the LHC (HL-LHC) will provide an order of magnitude more data starting from 2029, allowing precision tests of the properties of the Higgs boson and improved sensitivity to a wealth of new-physics scenarios. The HL-LHC will deliver to each of the ATLAS and CMS experiments approximately 170 million Higgs bosons and 120,000 Higgs-boson pairs over a period of about 10 years. By extrapolating Run 2 results to the HL-LHC dataset, this will increase the precision of most Higgs-boson coupling measurements: 2–4% precision on the couplings to W, Z and third-generation fermions; and approximately 50% precision on the self-coupling by combining the ATLAS and CMS datasets. The larger dataset will also give improved sensitivity to rare vector-boson scattering processes that will offer further insights into the Higgs sector. 

These precision measurements could reveal discrepancies with the SM predictions, which in turn could inform us about the energy scale of beyond-SM physics. In addition to improving SM measurements, the upgraded detectors and trigger systems being developed and constructed for the HL-LHC era will enable direct searches to better target new physics with challenging signatures. To achieve these goals, it will be essential to achieve a detailed understanding of the detector performance as well as to measure the integrated luminosity of the collected dataset to 1% precision.

Rising to the challenge 

To cope with the increased number of interactions when proton bunches collide at the HL-LHC, the ATLAS collaboration is working hard to upgrade its detectors with state-of-the-art instrumentation and technologies. These new detectors will need to cope with challenging radiation levels, higher data rates and an extreme high-occupancy environment with up to 200 proton–proton interactions per bunch crossing (see “Pileup” figure). Upgrades will include changes to the trigger and data-acquisition systems, a completely new inner tracker, as well as a new silicon timing detector (see “ATLAS Phase II” figure).

The trigger and data-acquisition system will need to cope with a readout rate of 1 MHz, which is about 10 times higher than today. To achieve this, ATLAS will use a new architecture with a level-0 trigger (the first-level hardware trigger) based on the calorimeter and muon systems. Building on the upgrades for Run 3, which started in July 2022, the calorimeter will include capabilities for triggering at higher pseudorapidity, up to |η| = 4. During HL-LHC running, the global trigger system will be required to handle 50 Tb/s as input and to decide within 10 μs whether each event should be recorded or discarded, allowing for more sophisticated algorithms to be run online for particle identification. All the detectors will require substantial upgrades to handle the additional acceptance rates from the trigger.  

The readout electronics for the electromagnetic, forward and hadronic end-cap liquid-argon calorimeters, along with the hadronic tile calorimeter, will be replaced. The full calorimeter systems, segmented into 192,320 cells that are read out individually, will be read out for every bunch crossing at the full 40 MHz to provide full-granularity information to the trigger. This will require changes to both front-end electronics and off-detector components. 

The muon system will also see significant upgrades to the on-detector electronics of the resistive plate chambers (RPCs) and thin-gap chambers (TGCs) responsible for triggering on muons, as well as the muon drift tubes (MDTs) responsible for measuring the curvature of the tracks precisely. The MDTs will also be used for the first time in the level-0 trigger decisions. These improvements will allow all data to be sent to the back-end at 40 MHz, removing the need for readout buffers on the detector itself. All hits in the detector will be used to perform trigger logic in hardware using field programmable gate-arrays. Additional improvements to increase the trigger acceptance for muons will come in the form of a new layer of RPCs to be installed in the inner barrel layer, along with new MDTs in the small sectors. The Muon New Small Wheel system was installed during Long Shutdown 2 (LS2) from 2019 to 2022 and is located inside the end-cap toroid magnet containing both triggering and precision tracking chambers. Additional RPC upgrades were also made in the barrel leading up to Run 3, and the TGCs will be upgraded in the endcap region of the muon system during LS3.

State-of-the-art tracking 

The success of the research programme at the HL-LHC will strongly rely on the tracking performance, which in turn determines the ability to efficiently identify hadrons containing b and c quarks, in addition to tau and other charged leptons. Reconstructing individual particles in the HL-LHC collision environment with thousands of charged particles being produced within a region of about 10 cm will be very challenging. The entire tracking system, presently consisting of pixel and strip detectors and the transition radiation tracker, will be replaced by a new all-silicon pixel and strip tracker – the ITk. This  will feature higher granularity, increased radiation hardness and readout electronics that allow higher data rates and a longer trigger latency. The new pixel detector will also extend the pseudorapidity coverage in the forward region from |η| < 2.5 to |η| < 4, increasing the acceptance for important physics processes like vector-boson fusion (see “Pixel perfection” image).

The ITk will comprise nine barrel layers, positioned at radii from 33 mm out to 1 m from the beam line, plus end-cap rings. It will be much more complex with respect to the present ATLAS tracker, featuring 10 times the number of strip channels and 60 times the number of pixel channels. The strip detectors will cover a total surface of 160 m² with 60 million readout channels, and the pixels an area of 13 m² with more than five billion readout channels. The innermost layer will be populated with radiation-hard 3D sensors, with pixel cells of 25 × 100 µm² in the barrel part and 50 × 50 µm² in the forward parts for improved tracking capabilities in the central and forward regions. Prototypes of the end-cap ring for the inner system and of the strip barrel stave are at an advanced stage (see “ITk prototyping” image). A unique feature of the trackers at the HL-LHC is that they will be operated for the first time with a serial powering scheme, in which a chain of modules is powered by a constant current. If the modules were to be powered in parallel, the high total current would lead to either high power losses or a large mass of cables within the volume of the detector, which would impact the tracking performance. 

Given the challenging conditions posed by the HL-LHC, ATLAS will construct a novel precision-timing silicon detector, the High-Granularity Timing Detector (HGTD), which provides a time resolution of 30 to 50 ps for charged particles. The detector will cover a pseudorapidity range of 2.4 < |η| < 4 and will comprise two double-sided silicon layers on each side of ATLAS with a total active area of 6.4 m². The precise timing information will allow the collaboration to disentangle proton–proton interactions in the same bunch crossing in the time dimension, complementing the impressive spatial resolution of the ITk. Low-gain avalanche diodes (see “Clocking tracks” image) provide timing information that can be associated with tracks in the forward regions, where they are more difficult to assign to individual interactions using spatial information. With a timing resolution six times smaller than the temporal spread of the beam spot, tracks emanating from collisions occurring very close in space but well-separated in time can be distinguished. This is particularly important in the forward region, where reduced longitudinal impact-parameter resolution limits the performance.

Building upon the insertable B-layer cooling system used since the start of Run 2, and to reduce the material budget, ATLAS will use a two-phase CO₂ cooling system for the entire silicon ITk and HGTD detectors. These will allow the detectors to be cooled to around –35 °C during the entire lifetime of the HL-LHC. The low temperature is required to protect the silicon sensors from the expected high radiation dose received during their lifetime. Two-phase CO₂ cooling is an environmentally friendly option compared to other suitable coolants. It provides a high heat transfer at reasonable flow parameters, a low viscosity (thus reducing the material used in the detector construction) and a well-suited temperature range for detector operations.

Luminous future

Precise knowledge of the luminosity is key for the ATLAS physics programme. To reach the goal of percent-level precision at the HL-LHC, ATLAS will upgrade the LUCID (Luminosity Cherenkov Integrating Detector) detector, a luminometer that is sensitive to charged particles produced at the interaction point. This is incredibly challenging given the number of interactions expected to be delivered by the machine, and the requirements on radiation hardness and long-term stability for the lifetime of the experiment. The HGTD will also provide online luminosity measurements on a bunch-by-bunch basis, and additional detector prototypes are being tested to provide the best possible precision for luminosity determination during HL-LHC running. Luminometers in ATLAS provide luminosity monitoring to the LHC every one to two seconds, which is required for efficient beam steering, machine optimisation and fast checking of running conditions. In the forward region, the zero-degree calorimeter, which is particularly important for determining the centrality in heavy-ion collisions, is also being redesigned for HL-LHC running.

The HL-LHC will deliver luminosities of up to 7.5 × 10³⁴ cm^–2s^–1, and ATLAS will record data at a rate 10 times higher than in Run 2. The ability to process and analyse these data depends heavily on R&D in software and computing, to make use of resource-efficient storage solutions and opportunities that paradigm-shifting improvements like heterogeneous computing, hardware accelerators and artificial intelligence can bring. This is needed to simulate and process the high-occupancy HL-LHC events, but also to provide a better theoretical description of the kinematics.

New era

The Phase-II upgrade projects described are only possible through collaborative efforts between universities and laboratories across the world. The research teams are currently working intensely to finalise the designs, establish the assembly and testing procedures, and in some cases start construction. They will all be installed and commissioned during LS3 in time for the start of Run 4, currently planned for 2029.

To cope with the increased number of interactions when proton bunches collide at the HL-LHC, the ATLAS collaboration is working hard to upgrade its detectors with state-of-the-art instrumentation and technologies

The HL-LHC will provide an order of magnitude more data recorded with a dramatically improved ATLAS detector. It will usher in a new era of precision tests of the SM, and of the Higgs sector in particular, while also enhancing sensitivity to rare processes and beyond-SM signatures. The HL-LHC physics programme relies on the successful and timely completion of the ambitious detector upgrade projects, pioneering full-scale systems with state-of-the-art detector technologies. If nature is harbouring physics beyond the SM at the TeV scale, then the HL-LHC will provide the chance to find it in the coming decades. 

The post A new ATLAS for the high-luminosity era appeared first on CERN Courier.

To exploit the HL-LHC physics potential, the CMS collaboration is building an optimised detector that pushes technologies to new heights. This major “Phase II” upgrade will enable the subdetectors to sustain the increased luminosity, which results in greater radiation damage and higher particle rates – the innermost pixel layer, for example, will see three billion hits per second per square centimetre. The CMS tracker and the calorimeter endcap will be replaced, a new minimum-ionising-particle precision timing detector (MTD) and a new luminosity detector will be installed, almost all of the existing electronics will be replaced, and additional muon forward stations will be mounted. 

High granularity 

The key to achieving the necessary HL-LHC performance is to enhance the granularity of the detector significantly. This reduces the maximum occupancy per readout cell while considerably increasing the readout bandwidth and processing power of the trigger system, thereby fully exploiting the higher collision rates. As a novelty, all CMS detector designs are tuned to allow full particle-flow reconstruction at the hardware-based level-1 trigger (operating at 40 MHz), while precision timing information, which contributes to the high-level-trigger decision, is exploited by highly optimised software mostly running on graphics processing units.

CMS is currently transitioning from the prototyping to the production phase on several major items. The novel gas electron multiplier (GEM) detector concept, used to detect muons produced in the very forward region, was deployed for the first time on a large scale during long shutdown 2 (LS2): 144 chambers in the first station are fully integrated into the ongoing data taking and the second station will be fully installed in a year-end technical stop before LS3 (see “GEM of a detector” image). Finishing endcap-muon upgrades in advance of LS3 allows the collaboration to minimise the repositioning of the CMS disks during LS3 and to reduce its overall duration. In this spirit, CMS has already finished the replacement of all front-end electronics of the cathode strip chambers. The replacement of the drift-tube electronics in the barrel muon detectors will take place in LS3, and an installed small-scale drift-tube demonstrator is already proving its performance.

The exceptional performance of the current all-silicon tracker provides a solid platform for even further improvements. A main novelty for Phase II is the level-1 track trigger, which reconstructs tracks with transverse momentum above 2 GeV, made available at a rate of 40 MHz. Profiting from the experience with pixels from Phase I, the whole Phase II tracker will use dual-phase CO₂ cooling, ultra-lightweight mechanics, DCDC converters for the powering of the outer tracker, and serial powering for the pixel system, thereby reducing the amount of material by a factor of two compared to today. To reduce the occupancies expected at the highest foreseeable number of collisions per bunch crossing (pile-up), the outer-tracker channel count will increase from 9 million strips to 42 million strips plus 170 million macro-pixels, providing unambiguous z-position measurements. With six barrel layers and five double-disks per endcap, the outer tracker is optimised not only for standalone tracking but also for vertexing, a prerequisite for the track trigger (see “Outer tracker” image). 

The outer tracker is already in production, having overcome most engineering and prototyping challenges. ASICs (application-specific integrated circuits) and sensors are being delivered and the order for the hybrids (which host integrated circuits and connections in the front-end modules) has been submitted. The inner tracker (pixel system) will feature two billion micro-pixels, compared to the 125 million at present. Four barrel layers plus 12 disks per endcap enable excellent track seeding and b-quark jet identification over the pseudorapidity range |η| < 4 (much broader than today’s |η| < 2.5). The inner tracker system aspects are understood, sensors will be ordered soon, and teams are waiting for the final readout ASIC to begin module production.

A new era of calorimetry 

The high-granularity calorimeter (HGCAL) in the forward region starts a new era of calorimetry. It is a radiation-tolerant 5D imaging calorimeter with spatial, energy and precision-timing information (see “HGCAL on display” and “High-granularity calorimetry” images). The deployment of machine-learning algorithms will further enhance its potential to establish the HGCAL as a blueprint for future calorimeters. The HGCAL has 6.4 million channels, two orders of magnitude more than the current endcap calorimeters, including both silicon cells (with an area of 0.5 or 1 cm²) and scintillator tiles (4 to 32 cm²) read out by silicon photomultipliers (SiPMs). The electromagnetic section consists of 26 active layers of silicon sensors interleaved with copper, copper-tungsten and lead absorbers. It is followed by the hadronic section, which is made of 21 active layers of silicon and scintillator tiles, separated by steel absorbers. All in all, 600 m² are equipped with silicon sensors (three times the area of the tracker) and 400 m² with SiPMs-on-tiles. 

The hexagonal-shaped sensors and the modules mimicking bee-hive structures are a design feature of the HGCAL. The hexagonal structure makes optimal use of the circular silicon wafer, therefore being cost-effective. With the sensor design and evaluation completed, mass production has started. The development of silicon sensors that are sufficiently radiation-tolerant for HL-LHC conditions, for both the HGCAL and the tracker, has taken considerable effort. It is also worth noting the use, for the first time in particle physics, of passive sensors processed on 8-inch wafers – another essential feature for covering larger areas at an affordable cost.

The electromagnetic calorimeter (ECAL) barrel and its 61,200 lead-tungstate crystals, which were instrumental in the discovery of the Higgs boson via its decay to two photons, will be retained and equipped with new front-end electronics capable of sustaining the higher rates and trigger latency (see “ECAL upgrades” image). Faster signal processing will result in a much-improved time resolution of 30 ps for high-energy photons (and electrons), enabling precise primary-vertex determination. 

The novel track trigger and the much-improved cell granularity allow the full implementation of the particle-flow reconstruction (based on field-programmable gate arrays, FPGAs) already in the level-1 trigger. The single-crystal granularity that will be provided by the ECAL barrel, even at the trigger level, together with the 3D imaging features of the HGCAL, provide crucial information to precisely follow the path of all particles through the entire detector. This opens the possibility of establishing a full menu of cross-particle triggers and of using FGPA-based machine learning at the level-1 trigger. Trigger algorithms have been prototyped in FPGAs and demonstrated in a multi-board “slice test”. In order to efficiently process the 63 Tb/s input bandwidth, the system is equipped with 250 FPGAs, with an output rate of 750 kHz and a latency of 12.5 μs.

Bright times ahead

For the luminosity measurement, CMS is following a strategy analogous to the one for the trigger, exploiting data from various subdetectors with the ambitious goal of 1% offline (2% online) uncertainty. Achieving this precision requires an understanding of the detector systematic effects, such as linearity and stability, at the per-mille level. A dedicated silicon-pad-based luminometer with an asynchronous readout will help in quantifying systematic uncertainties and beam-related backgrounds, and will play an essential role in the CMS (and LHC accelerator) commissioning.

CMS will enter further uncharted territory in the precision-timing domain with the MTD. For the barrel system, the challenge is to adapt the cost-effective LYSO crystal + SiPM technology, similar to that used in PET scanners, to sustain the HL-LHC rates and radiation. An interesting detail is the use of micro-Peltier elements (thermo-electric coolers) to further decrease the local temperature on the SiPMs, thus counteracting the effects of radiation damage. The endcaps use a new twist on well-established silicon tracking technology: low-gain avalanche detectors, with an additional thin implant within the sensor to generate internal gain. The MTD covers the full solid angle up to |η| = 3 to mitigate pile-up, boost the sensitivity to searches for long-lived particles, and enhance the physics capabilities during heavy-ion runs by providing particle identification capability via time-of-flight measurements.

The high-granularity calorimeter in the forward region starts a new era of calorimetry

All these individual systems are combined into the CMS Phase II detector. Technical coordination is choreographing the integration and has established a detailed schedule for LS3, taking all the detector and external requirements and constraints into account. To maximise the time for detector installation and commissioning during LS3, a huge effort is ongoing in preparing the site in advance. New buildings are already under construction to house the new service infrastructure, such as chillers for the detector CO₂ cooling, uninterrupted power systems and detector- and dry-gas systems. During LS3, the biggest challenge will be to decommission all the legacy systems, including services, that will be replaced by new detectors, and then fit all the new pieces together.

The CMS Phase-II upgrade is a multi-faceted project involving more than 2000 scientists, students and engineers from institutes and industrial companies in more than 50 countries. Initially discussed prior to the first LHC operation and defined by the CMS technical proposal in 2015, the CMS Phase II upgrade together with upgrades to the other LHC detectors will ensure that maximal physics is extracted under the challenging conditions of the HL-LHC. 

The post CMS prepares for Phase II appeared first on CERN Courier.

It’s now two years since a joint research group from SPring-8 Center, which is managed by Japan’s premier research agency RIKEN, and the Japan Synchrotron Radiation Research Institute (JASRI), responsible for promoting the use of SPring-8, succeeded in utilising the linear accelerator of the SACLA X-ray free-electron laser (XFEL) facility as an injector for the SPring-8 storage ring. 

The upsides were immediate, impressive and – crucially – sustained. For starters, the 25-year-old injector of SPring-8, which hitherto was used exclusively for beam injection, has been superseded by the SACLA linear accelerator – reducing the electricity consumption needed to support SPring-8 operation by roughly 20%. Equally significant, the quality of the electron beam injected into the storage ring has been enhanced markedly – a breakthrough that will underpin the upgrade plan of SPring-8 to a fourth-generation light source (SPring-8-II) capable of generating X-ray beams hundreds of times brighter than the current facility. 

Legacy problems, creative solutions

By way of context, the previous, dedicated injector for the SPring-8 storage ring consisted of a 1 GeV linear accelerator and an 8 GeV synchrotron booster. The emittance of the resulting injection beam was about 200 nm-rad, which is far larger than the specification of the future SPring-8-II (at 10 nm-rad). There were legacy technology issues as well: both injector accelerators were more than 25 years old, while the associated (and somewhat decrepit) high-voltage power substation was itself in need of a root-and-branch overhaul. 

Cue some creative thinking and the game-changing idea of deploying SACLA’s low-emittance electron beam for SPring-8 beam injection (and in parallel to its core function as a source of XFEL photon beams for front-line research). Herein an engineering win-win began to take shape: on the one hand, the opportunity to decommission (rather than renovate) the high-voltage substation; on the other, to simultaneously reduce SPring-8’s electricity consumption significantly by shutting down the old injector accelerators (which were always maintained in operational mode despite the only intermittent requirement for beam injection). Underpinning it all is the fact that the SACLA linear accelerator is always online for the XFEL research users, so no additional cost or energy consumption accrues when sending a small number of electron-beam pulses from SACLA to the SPring-8 storage ring.

In the early design phase of SACLA (around 2008), and with engineers anticipating the future possibility of beam injection to SPring-8, the nominal beam energy of SACLA was set at 8 GeV to match the SPring-8 storage ring. The direction of the SACLA electron beam was also fixed towards SPring-8 to facilitate the envisaged beam-injection
scenario. To join things up, the two accelerators are linked by a beam transport line – the XFEL to Storage ring Beam Transport (XSBT) – which was constructed at the same time as the SACLA facility (see images “Better together” and “Joined up”). 

When it comes to the technical specifics, the SACLA beam repetition rate is set at 60 Hz, with the electron-beam pulses distributed on a pulse-by-pulse basis in three directions with the help of a “kicker” magnet: along two XFEL beamlines (BL2 and BL3) and down the XSBT beamline. What’s more, the electron-beam energies for XFEL user experiments are often adjusted in a range between 5 and 8 GeV depending on laser wavelengths, while the energy needs to be fixed at 8 GeV for the beam injection. It is therefore essential to control the electron-beam parameters pulse-by-pulse to allow XFEL user experiments and the SPring-8 beam injection to proceed in parallel. 

Synchronisation is nothing without control

Operationally, the preparation of the SACLA beam-injection scheme took about two years in design, planning and commissioning. The first task for the project team was to synchronise the two accelerators, given that they run on different reference clock frequencies (238 MHz for SACLA; 508 MHz for SPring-8). Since the two frequencies do not have a harmonic relation, the injection timing naturally goes off with respect to the target RF bucket of SPring-8 by a maximum ±2.1 ns. A novel timing system was subsequently developed to provide the necessary synchronisation. 

In top-up injection mode, which keeps a constant stored current within the storage ring, SPring-8 sends a beam request to SACLA when the stored current decreases under a certain threshold. Once SACLA receives the request, the timing system first searches out a point where the timing difference is at a minimum. By delaying the beam injection up to 197 µs, there should be a point where the timing difference becomes smaller than 105 ps. In a second step, a slight frequency modulation is applied to the SACLA 238 MHz reference clock, such that SACLA and SPring-8 are finally synchronised to within 3.8 ps (RMS).

Another significant piece of work involved retrofitting the accelerator control system. To change the accelerator parameters pulse-by-pulse, it is necessary for accelerator components to “know” the destination of the next beam pulse. That granular data (at the level of an individual pulse) is therefore sent through a “reflective memory network” to key components and subsystems – for example, RF sources and magnet power supplies – such that these devices can then operate with prestored parameters corresponding to the relevant beam destination. 

Meanwhile, all diagnostic data are saved in a database with a pulse tag number so that the measured data, such as beam trajectories and charges, can be distinguished among the three beam destinations (BL2, BL3 and XSBT). It is like there are three accelerators independently running with different beam energies and parameters. In day-to-day operation, three operators adjust and tune the accelerators by looking at the monitor and control panels for the three beams versus the respective destinations. Using the pulse tag number, XFEL users are also able to see which pulses were used for the beam injection, so that these pulses can be eliminated from their experimental data. 

A final core deliverable for the project team was to ensure the bulletproof reliability of SACLA – since the storage ring cannot operate without beam injection. In short, if the linear accelerator of SACLA fails to provide electron beams, close to 60 experiments on the SPring-8 beamlines are at risk of grinding to a halt. Redundancy is the key here: to promptly recover from unexpected troubles, the team installed back-up components for crucial accelerator devices, such as the electron gun, kicker magnet and RF sources.  

Going live

During the early-stage evaluation of the new beam-injection scheme, two other issues came into play: electron bunch purity and magnetic hysteresis of the kicker magnet. The electron bunch purity is a ratio of electron charges contained in an electron-injected RF bucket and an empty bucket on the storage ring. 

It is an important figure of merit – not least for ensuring low background noise in time-resolved experiments. A bunch purity of between 10^–8 and 10^–10 is typically required at SPring-8, while the electron bunch charge of SACLA is around 200 pC – i.e. even a single electron outside the beam pulse could degrade the bunch purity. 

It turned out, however, that a small number of electrons were detected 18 ns after the main beam pulse during the initial experimental runs. After detailed investigation, the project team found that these electrons were slipping out from the main pulse and making a round trip between two RF cavities at the injector section of SACLA. Consequently, they were delayed by 18 ns and being injected into unexpected RF buckets on the storage ring. The solution: remove the delayed electrons using an electric sweeper and an RF knockout system – a breakthrough that, in turn, yielded the required bunch purity of 10^–10. 

At the far-end of SACLA’s linear accelerator, electron-beam pulses are deflected horizontally in three directions by a kicker magnet. The polarity of the kicker current is negative for BL2, zero for BL3 and positive for XSBT. As a consequence, the beam orbits of the pulses just after the beam injection (i.e. two to three times a minute) deviate from the optimum trajectory inside the XFEL undulators – seriously degrading pointing stability and laser power within the SACLA beamlines. To overcome this issue, the excitation pattern of the kicker magnet is modified slightly after the beam injection, such that the hysteresis effect is now suppressed within an angular deviation of 1 µrad (i.e. less than 10 % of the laser spot size). 

With those “issues arising” addressed successfully by the project team, it’s instructive to look at the high-level operational performance of the new beam-injection arrangement. To fill up the storage ring with a nominal stored current of 100 mA, the electron beam is injected at 10 Hz from SACLA. The process takes about 10 minutes – roughly twice as fast as the old injector. Once the storage ring is filled, top-up injection gets underway to keep the stored current at a constant level. In top-up mode, the electron beam is injected typically 2–3 times every minute. Measuring the transverse beam sizes at the injection point of SPring-8 shows that the size of the electron beam from SACLA is significantly narrower versus that from the old injector, with the beam quality represented by emittance improving from 200 nm-rad to 1 nm-rad – more than satisfying the criteria for the future SPring-8-II.

Green machines

Alongside those sustained performance improvements, there are other notable wins to report for the SACLA beam-injection arrangement. After a probation period of six months, the old SPring-8 injector and its power station were shut down in April 2021, yielding a 5 MW saving in electricity consumption and an impressive 20% reduction in the SPring-8 power bill (i.e. versus current SPring-8 plus the old injector).

Further operational efficiencies are in the works for SPring-8-II given the global surge in energy prices and the shared commitment (with SACLA) towards carbon neutrality by 2050. By using cutting-edge, short-period, in-vacuum undulator technologies in SPring-8-II, for example, the electron-beam energy will be reduced from 8 GeV to 6 GeV without changing the X-ray radiation energy range. Replacing accelerator electromagnets with permanent magnets will enable additional reductions in power consumption. The ultimate goal of SPring-8-II, and with user operation pencilled in to begin no later than 2030, is a 50% reduction in power consumption versus the current SPring-8.

The ultimate goal is a 50% reduction in power consumption for SPring-8-II versus the current SPring-8

Similarly ambitious plans are taking shape for the SACLA-II upgrade, which will take place after the completion of SPring-8-II. The end-game: a 1 kHz repetition rate using conventional (rather than superconducting RF) accelerator technologies. With traditional RF acceleration, of course, more than 99.99 % of the input power is dissipated as heat – rather than accelerating the electron beam – so the challenge for SACLA-II is to boost this extremely low conversion efficiency, thereby increasing the repetition rate without increasing the power consumption. 

While none of this will be straightforward, it’s evident that the path to a “greener” and more sustainable accelerator complex is rapidly coming into view.

The post SACLA and SPring-8: a roadmap towards sustainable science appeared first on CERN Courier.

Fundamentally, this is a question of supply (high-quality cancer treatment) versus demand (rising cancer incidence) for India – not least when it comes to the challenges associated with rolling out accessible and affordable radiation therapy facilities at the national level. Right now, there are around 545 clinical radiotherapy units across India (180 ⁶⁰Co-based teletherapy systems and 365 electron linacs). Most of the e-linacs are supplied by commercial manufacturers, with 50% of these systems located in private hospitals – and therefore beyond the reach of the majority of Indian citizens. 

To drive down the cost of radiotherapy treatment, while simultaneously opening up access to more cancer patients, the Society for Applied Microwave Electronics Engineering and Research (SAMEER) in Mumbai has been prioritising technology innovation in e-linacs for several decades (with financial support from the central government’s Ministry of Electronics and Information Technology, also known as MeitY). 

Accessibility, affordability, availability 

A case study in this regard is the medical electronics division of SAMEER, which initiated an R&D programme for a 4 MeV e-linac for cancer therapy in the late 1980s. The initial outcome: an S-band, side-coupled linac (operating at π/2 mode at 2.998 GHz) developed for electron acceleration. The SAMEER development team later integrated the linac with other core subsystems in collaboration with the Central Scientific Instruments Organisation, Chandigarh, and the Post Graduate Institute of Medical Education and Research (PGIMER), Chandigarh, with the completed linac commissioned at PGIMER in 1991. 

This original machine was called Jeevan Jyoti-I. SAMEER engineers went on to build three more e-linac variations on the Jeevan Jyoti-I theme, with all units duly commissioned and operating in hospitals. Subsequently, under the Indian government’s Jai Vigyan initiative, SAMEER built six more radiotherapy units (with an increased energy of 6 MV) and installed these systems in hospitals. One more machine is being commissioned in 2022 – initially using commercial microwave sources from SAMEER (though these will eventually be replaced with a domestically developed 2.6 MW magnetron).

Multipurpose proton accelerators

India’s Department of Atomic Energy (DAE) plans to exploit the country’s rich natural sources of thorium to bolster the domestic nuclear energy programme, simultaneously exploring new methods for dealing with high-level nuclear waste as well as the at-scale production of medical radioisotopes for the diagnosis and treatment of cancer.

Consider the so-called accelerator-driven subcritical reactor (ADSR), a next-generation nuclear reactor design formed by coupling a substantially subcritical nuclear reactor core (using thorium as fuel) with a high-intensity, high-energy proton accelerator. The latter generates a copious beam of spallation neutrons to sustain the fission process – activating the thorium without needing to make the reactor critical (i.e. turning off the proton beam results in immediate and safe shut-down of the reactor). Another benefit of the ADSR scheme is the relatively short half-lives of the waste products.

Within this context, DAE’s R&D laboratories have started work on a high-current 1 GeV proton accelerator (see “Collective endeavour” figure). In the first phase of construction of a 20 MeV normal-conducting linac at Bhabha Atomic Research Centre (BARC), scientists accelerated a 2 mA proton beam from an ion source using a four-vane RF quadrupole (generating a 3 MeV proton beam with 65% transmission). Earlier this year, the BARC team boosted the proton energy to 6.8 MeV through the first drift-tube linac (with a peak beam current of 2.5 mA and an average beam current of 1 μA with 93% transmission). At Raja Ramanna Centre for Advanced Technology (RRCAT), meanwhile, several warm-front-end ion sources and associated subsystems are under construction (including low-energy beam transport, RF quadrupoles, medium-energy beam transport and a drift-tube linac). 

Operationally, collaboration is a defining theme of India’s R&D effort on proton accelerators – not least through its scientists’ direct participation in the Proton Improvement Plan II (PIP-II), an essential upgrade and ambitious reimagining of the Fermilab accelerator complex in the US. Several Indian institutions are front-and-centre in the PIP-II initiative, designing and developing room-temperature and superconducting magnets, superconducting RF cavities, cryomodules and RF amplifiers for the PIP-II project team. 

BARC and the Inter-University Accelerator Centre (IUAC) in New Delhi, for example, initially supplied two single-spoke-resonator cavities for testing at Fermilab, while end-to-end infrastructure for niobium-cavity fabrication and testing has been established at RRCAT. Several niobium superconducting cavities – required in both the PIP-II project and the Indian proton accelerator programme – have since been fabricatedand tested successfully.

Innovation pathways

One thing is clear: India’s e-linac R&D effort continues to gather momentum. The next step is to enhance the technology for dual photon energies (6 and 15 MeV) from the same linac, along with multiple electron energies (from 6 to 18 MeV) for treatment. A prototype of a novel dual-energy linac has already been put through its paces, delivering beam-on-target at SAMEER. The energy is varied by introducing a plunger in the coupling cavity in the acceleration section. Industry partners are being sought as the system undergoes final quality assurance and control checks.  

Parallel technology programmes – covering both e-linacs and proton cyclotrons – are also underway to support domestic production of medical radioisotopes used in the diagnosis and treatment of cancer. For example, a 30 MeV, 5–10 kW linac project (incorporating two 15 MeV sections) is being lined up for the production of ^99mTc from ⁹⁹Mo (the former being required in a nuclear imaging procedure called single-photon-emission computerised tomography, commonly known as SPECT). The ⁹⁹Mo will be produced from ¹⁰⁰Mo using Bremsstrahlung photons, with the latter emitted after accelerated electrons are incident on a target. Tests of the first accelerating structure (15 MeV) are in progress and the full energy of 30 MeV is expected to come online next year. 

India and CERN: a win–win partnership

Following India’s associate membership at CERN from 2017, the country’s scientists and engineers continue to build on a rich and diverse legacy of contributions spanning core accelerator technologies and participation in front-line high-energy physics experiments. This is a legacy that extends across more than 50 years of collaboration. In the 1990s, for example, the RRCAT contributed to LEP, while the Indian High-Energy Heavy Ion Physics Team contributed to the WA93 experiment at the CERN-SPS. An international cooperation agreement between India’s Department of Atomic Energy (DAE) and CERN was signed in 1992 to deepen ties and extend the scientific and technical cooperation between India and CERN. Those developments, in turn, paved the way for the decision (in 1996) of India’s Atomic Energy Commission to take part in the construction of the LHC – specifically, to contribute to the development of the CMS and ALICE detectors. India became a CERN Observer State in 2002, and the success of the DAE–CERN partnership on the LHC led to a new cooperation on novel accelerator technologies, shaping DAE’s participation in CERN’s Linac4, SPL and CTF3 projects. 

Elsewhere, the Variable Energy Cyclotron Centre (VECC) in Kolkata is leading a project to build an 18 MeV medical cyclotron – a machine that will reduce the cost of production for positron-emitting radioisotopes. In terms of operational specifics: the system will accelerate negative hydrogen ions (H^–) from an external, multicusp volume ion source, while a carbon stripper foil will alter the charge state of the ions from negative to positive ahead of extraction. Progress to date is encouraging: engineering design of the main magnet is complete and a 1 mA current has been extracted from the H^– ion source. 

Further technology innovation is evident in the field of hadron therapy, which uses proton or ion beams to deliver precision tumour targeting with zero exit dose – a capability that clinicians estimate could improve therapeutic outcomes in 15–20% of cancer patients who receive radiotherapy. Recognising the potential here, Indian clinics have recently purchased and installed two 230 MeV proton cyclotrons, supplied by Belgian equipment maker IBA, in a pivot towards next-generation cancer treatments. 

Further progress has been reported by a collaboration between SAMEER and KEK, Japan’s High-Energy Accelerator Research Organisation. Jointly, the two partners have completed conceptual design studies for a multi-ion therapy machine based on a novel digital accelerator concept. The system is basically a fast-cycling induction synchrotron with a specialised beam-handling capability. (For context, the accelerating devices of a conventional synchrotron, such as RF cavities, are replaced with induction devices in an induction synchrotron.) It is possible, for example, to inject particles at nearly 200 kV DC directly into the main ring and, as such, the induction synchrotron does not need a separate injector. 

In a related initiative, the Tata Memorial Centre Mumbai, and Raja Ramanna Centre for Advanced Technology (RRCAT), Indore, have come up with a preliminary design for a 2 MeV injector and a 70–250 MeV proton synchrotron that may also be suitable for variable-energy beam delivery and other ion-beam therapies.

The post India sets its sights on linac innovation appeared first on CERN Courier.

It’s 12 months since the International Center for Quantum-field Measurement Systems for Studies of the Universe and Particles (or QUP for short) was unveiled as the latest addition to the World Premier International Research Center Initiative (WPI) run by Japan’s Ministry of Education, Culture, Sports, Science and Technology (MEXT). Based in Tsukuba City, 60 km north-east of Tokyo, the new centre represents a high-profile addition to the scientific powerhouse that is KEK, Japan’s High Energy Accelerator Research Organisation. 

Within KEK, QUP has since assumed its place alongside the organisation’s other flagship research laboratories – among them the Institute of Particle and Nuclear Studies (IPNS), the Accelerator Laboratory (ACCL) and the Japan Proton Accelerator Research Complex (J-PARC) – in order to ensure that the outcomes of its ambitious research endeavours dovetail with, and reinforce, KEK’s core discovery programme in elementary particle physics. Here QUP director Masashi Hazumi tells CERN Courier about the centre’s progress to date and the opportunities for talented early-career scientists prepared to take risks and look beyond the comfort zone of their core disciplinary specialisms.

How would you pitch QUP to a talented postdoc thinking about the next big career move?

QUP’s mission is to “bring new eyes to humanity” by inventing advanced measurement systems – novel electronic and quantum detectors that will unlock exciting discoveries in cosmology and particle physics. Examples include superconducting detectors to study cosmic inflation (for the LiteBIRD space mission) and low-temperature quasiparticle detection systems to search for “light dark matter”. We are also keen on applying our unique capabilities to broader academic fields and industrial and societal applications – a case in point being our close engagement with Toyota Central R&D Laboratories. 

In this way, QUP will return to the essence of physics, conducting interdisciplinary research to develop new methodologies while integrating particle physics, astrophysics, condensed-matter physics, measurement science, and systems science. QUP’s inventions and innovations will exploit the most fundamental object in nature – the quantum field – and thereby open up a new era in measurement science: quantum-field measurement systemology.

What sets the QUP approach apart from other quantum measurement centres? 

QUP’s strength lies in the breadth of technologies covered and the ability to transition seamlessly between studies of fundamental physics to the execution of large-scale projects on next-generation scientific instruments and quantum technologies. The aim is simple: to create a cross-disciplinary “melting pot” that encourages a fusion of ideas across diverse fields of science, technology and engineering. As such, we’re recruiting a team of “multidisciplinarians” – scientists who can apply their domain knowledge and expertise creatively and flexibly across subject boundaries. 

A good example is the quantum diamond sensor – an enabling technology that exploits so-called NV defects in the carbon lattice – which QUP is developing to support precise temperature measurements of instrumentation (down to the 1 mK level at room temperature) in future studies of the cosmic microwave background (CMB). Notably, that same quantum sensing technology is also attracting early-stage interest from our colleagues at Toyota, with QUP particle physicists and industrial scientists openly sharing ideas. Unanticipated connections like this can create intriguing opportunities for young scientists, opening up new research pathways and long-term career opportunities. 

How important is QUP’s positioning as part of the KEK research organisation? 

QUP is unique among Japan’s WPI programmes because it is the only centre focused on measurement systems, while the integration within KEK means collaboration is hard-wired into our working model. We are already establishing networks to link QUP scientists with researchers across KEK’s accelerator facilities and laboratories. An early success story is the QUP/KEK machine-learning research cluster, which is exploiting AI in a range of high-energy physics contexts and industrial applications (e.g. autonomous vehicles). 

Presumably that collaborative, open mindset extends beyond KEK? 

Correct. We are in the process of establishing three satellite sites for QUP – at Toyota Central R&D Laboratories in Aichi; the Japan Aerospace Exploration Agency (JAXA) Institute of Space and Astronautical Science (ISAS) in Kanagawa; and the University of California, Berkeley, in the US. These activities are already bearing fruit: Hideo Iizuka, a senior scientist at Toyota and one of our principal investigators at QUP, is developing applications of the Casimir effect (the attractive force between two surfaces in a vacuum), with a long-term goal of demonstrating a zero-friction shaft bearing for energy-efficient vehicles. 

You highlighted the LiteBIRD space mission earlier. What is QUP’s role in LiteBIRD?  

One of QUP’s flagship projects centres around the contribution we’re making to the JAXA LiteBIRD space mission, which will study aspects of primordial cosmology and fundamental physics. I am one of the founders of LiteBIRD, an international, large-class mission with an expected launch date in the late 2020s using JAXA’s H3 rocket. When deployed, LiteBIRD will orbit the Sun–Earth Lagrangian point L2, where it will map CMB polarisation over the entire sky for three years. The primary scientific objective is to search for the signal from cosmic inflation, either making a discovery or ruling out well-motivated inflationary models of the universe. LiteBIRD will also provide insights into the quantum nature of gravity and new physics beyond the standard models of particle physics and cosmology. The focus of QUP’s contribution is development of the superconducting detector subsystem for LiteBIRD’s low-frequency telescope.

Project Q is another of QUP’s flagship initiatives. What is it?

Project Q is still a work-in-progress. Essentially, we are putting together a framework to invent and develop a novel system for the measurement of a new quantum field. Last month, as part of the requirements-gathering exercise, QUP and the KEK Theory Center jointly organised a dedicated workshop called “Toward Project Q”. The hybrid event attracted 91 participants – a mix of QUP staff and international colleagues – who shared a range of ideas on potential lines of enquiry for Project Q, including cryogenic measurements, space missions, accelerator and non-accelerator experiments, as well as the use of novel quantum sensors. Watch this space.

What are your near-term priorities as director of QUP?

My number-one priority is to hire the best researchers and position QUP for long-term scientific success. The open nature of Project Q represents a useful conversation-starter in this regard. We have 27 scientists on the staff just now and the plan is to grow the research team to about 70 people by early 2024 – a cohort that will ultimately comprise around 15 principal investigators supported by a team of research professors and postdocs (and with WPI guidelines stating that 30% or more of the QUP team should eventually come from abroad). When it comes to recruitment, I’m looking for scientists who are enterprising, creative and not afraid to take risks – there may well be some candidates who fit the profile among the CERN Courier readership! I like that sort of spirit. If you go big, the success rate may not be high, but unexpected insights and opportunities will often emerge. 

The post QUP emphasises its KEK connections appeared first on CERN Courier.

RAON is big science writ large. By accessing exotic and as-yet-undiscovered radioisotopes, RAON will address a broad-scope research roadmap when it comes online for initial user experiments in two years’ time. By extension, the laboratory will generate a wealth of data to advance physicists’ fundamental understanding of the nucleus; provide novel insights about the origins of the chemical elements in the universe; and enable experiments to explore physics beyond the Standard Model. Equally significant, RAON will produce research quantities of rare isotopes to underpin diverse applied R&D efforts spanning, for example, the diagnosis and treatment of cancer, safe disposal of spent nuclear fuels, and the lossless storage of electrical energy. 

It’s RAON’s combined production scheme, however, that sets it apart from other heavy-ion accelerator laboratories. Specifically, a twin-track approach that exploits – separately as well as in tandem – two methods for producing rare isotopes: isotope separation online (ISOL) and in-flight fragmentation (IF). For context, ISOL involves the acceleration of light ions (e.g. protons) and their collision with a heavy-element target (e.g. uranium), with a large abundance of rare (and high-purity) isotopes extracted following fragmentation of the target. With IF, on the other hand, accelerated heavy ions (e.g. uranium) collide with a light-element target (e.g. carbon), with strong magnets extracting rare isotopes of interest from many kinds of very fast-moving, fragmented heavy-ion beams.  

RAON is, by some way, South Korea’s biggest big science endeavour to date

Myeun Kwon, director of RISP and RAON

Here Myeun Kwon, director of RISP and RAON, tells CERN Courier how the new facility is taking shape with help from a network of partnerships across the scientific community and industry. 

What differentiates RAON’s scientific mission from other heavy-ion accelerator facilities?

We are developing RAON, first and foremost, to access the unexplored regions of the nuclear landscape. Upon completion, RAON will provide a first-of-its-kind production facility, combining ISOL as a first step and IF systems in a second step to produce and study the more exotic radioisotope beams – in fact, up to 80% of all the isotopes predicted to exist for elements below uranium. There are a number of studies – theoretical and experimental – which suggest that such a two-step process will expand the horizon for radioisotope production dramatically. 

While other heavy-ion accelerators rely exclusively on either ISOL or IF, RAON will be the first to exploit a combined ISOLIF production scheme – while simultaneously making ISOL and IF available to users as stand-alone processes. As such, RAON is expected to increase the rate of discovery of rare isotopes, whilst producing them in larger quantities and in greater variety.

Building blocks: the RAON accelerator facility

Upon completion, the RAON accelerator will generate heavy and light ion beams at a wide range of momenta – up to 200 MeV/nucleon for uranium and 600 MeV for protons (and with a beam current range from 8.3 pμA for uranium and 660 pμA for protons). 

In terms of the core building blocks, RAON comprises an injector system and three discrete superconducting linac sections, the superconducting cavities of which are phased independently and operated at three different frequencies (81.25, 162.5 and 325 MHz).

The low-energy superconducting linac section (SCL3) and the high-energy superconducting linac (SCL2) are connected by a post-accelerator driver linac (P2DT), which consists of a charge-stripper, two rebunchers and a 180° bending system. 

The injector system accelerates a heavy-ion beam to 500 keV/nucleon and creates the desired bunch structure for injection into the SCL3 linac. 

The injector comprises two electron cyclotron ion sources (ECR-IS), a low-energy beam transport section (LEBT), an RF quadrupole (RFQ) and a medium-energy beam transport system (MEBT).

The LEBT is designed to transport and match ion beams extracted from the ECR-IS to the RFQ; electrostatic quadrupoles are chosen for transport and focusing because these are more suitable for the LEBT’s low-velocity beams.

The RFQ (approx. 5 m long with a four-vane structure) is designed to accelerate ion beams from 10 keV/nucleon to 500 keV/nucleon at 81.25 MHz of the resonance frequency. 

The MEBT comprises 11 room-temperature quadrupole magnets to transport and focus the ion beams, with four bunching cavities (operating at 81.25 MHz of resonance frequency) arranged to match the longitudinal beam size to SCL3.

Phase II of the accelerator roll-out (due for completion in 2025) involves the construction and commissioning of the high-energy superconducting linac (SCL2).

Completion of Phase II of RAON will see the launch of a co-located laboratory to evaluate next-generation radiotherapy modalities for the treatment of cancer – for example, the combined use of ¹¹C particle beams for localised radiotherapy and in situ gamma-ray imaging of solid tumours (so-called theranostics). 

How important are partnerships – domestic and international – for the successful delivery of the RAON initiative? 

RAON is, by some way, South Korea’s biggest big science endeavour to date. Put simply, the project would not be possible without our extensive R&D partnerships, supporting us with the co-development of core enabling technologies for the accelerator facility and the experimental systems for RAON’s front-line research programme. We have a network of Korean universities and research institutes, for example, working on accelerator design and development, as well as the manufacture and testing of superconducting components and subsystems. 

International collaboration is front-and-centre as well, with diverse technology contributions from the likes of TRIUMF (Canada), RIKEN and KEK (both Japan), the Institute of High Energy Physics (IHEP, China), the Institute for Nuclear Physics (INFN, Italy) and the European Spallation Source (ESS, Sweden). At a more strategic level, we rely on broad engagement and oversight from a network of scientific and engineering experts represented on our international/technical supervisory committees.

What does RAON’s engagement with industry look like? 

We’re pursuing a mixed model with industry – using off-the-shelf technologies when appropriate to manage our capital outlay, but also co-developing unique breakthrough technologies that can subsequently be transferred and exploited more widely by industry. A good example of the latter is Vitzro Tech, a domestic manufacturer that we engaged on bespoke development and manufacture of a portfolio of niobium superconducting RF cavities, cryomodules and cryogenic distribution lines for key legs of the accelerator facility. Vitzro Tech’s inputs are fundamental to the project’s long-term success and the expectation is that the technologies the company developed for RAON will, in time, be offered commercially to other big science facilities – a case study in downstream innovation. 

Presumably, you need to forge close links with equipment manufacturers at home and abroad?

Correct. Big science is all about collaboration, so the priority, from the off, is to have tight communication with your industry vendors. We have domestic manufacturers, for example, that have supplied us with a range of commercially available accelerator technologies – advanced magnets, vacuum systems and associated instrumentation – while international manufacturers also feature prominently in the project supply chain. The RAON cryoplant is a case in a point – a turnkey system developed specifically for RAON by our technology partner Air Liquide of France. 

How has the project timeline been affected by the COVID-19 pandemic? 

RAON depends on equipment deliveries from regional and international technology partners, so some supply-chain disruption was inevitable as a result of the pandemic. Notwithstanding the logistical obstacles, we have registered significant progress along many coordinates over the past three years. The construction of all buildings and supporting facilities was completed in 2021, while the low-energy linac – which includes two types of superconducting RF cavities – and its associated cryoplant, ISOL facilities (with cyclotron) and experimental systems (seven in all) are also complete. 

A significant commissioning milestone was reached in October 2022 with the first argon-ion beams accelerated by the low-energy superconducting linac, with all the linac subsystems – including quarter-wave and half-wave resonator cavities – cooled down to cryogenic temperatures (see “Building blocks: the RAON accelerator facility”). The mechanical installation and commissioning of the associated cryoplant (4.2 kW cooling capacity as the equivalent heat load at 4.5 K) was completed back in August 2022, with the “cold box” connected to the main helium distribution line.

What are the next steps for RAON? 

We are now in the middle of commissioning the low-energy superconducting linac and aim to complete that process early next year. We envisage a similar commissioning timeline for the ISOL facility (with 70 MeV proton cyclotron) and the low-energy experimental facilities such as KoBRA (Korea Broad acceptance Recoil Spectrometer and Apparatus). In the middle of 2023, we will combine all of these building blocks for initial radioisotope production, with preparations for the first round of user experiments (at low energies) taking another year or so through to autumn 2024. Phase two of the RAON installation involves the construction and commissioning of the high-energy superconducting linac. 

The post RAON’s rare-isotope ambitions appeared first on CERN Courier.

Headquartered in Islamabad, PINSTECH is a premier R&D institute within PAEC and, by extension, one of Pakistan’s leading research centres. The institute’s wide-ranging research programme spans, among other things, isotope production and applications, materials science, radiation protection and health physics, as well as neutron science. That R&D effort is augmented by two operational nuclear research reactors: Pakistan Research Reactor-1 is a 10 MW pool-type reactor which is used to produce radioisotopes for medical applications; Pakistan Research Reactor-2 is a smaller reactor that’s used, chiefly, for neutron activation and teaching/training activities. 

Operationally, PINSTECH has facilities for the production of a range of reactor-based radioisotopes – including ⁹⁹Mo, ^99mTc generators, ¹³¹I, and ³²P – all of which are supplied to nuclear medicine centres across the country on a rolling basis. A key element of this programme is PINSTECH’s production of freeze-dried, radiopharmaceutical in-vivo diagnostic kits for nationwide distribution. 

During radioisotope production, target materials are placed into the research reactor for neutron irradiation, after which the irradiated targets are transferred into the “hot cells” of the facility for chemical separation, purification, quality control and dispatch. The Pakistan Nuclear Regulatory Authority and Drug Regulatory Authority of Pakistan regulate the end-to-end production process. 

Elsewhere within PINSTECH, and with support from CERN, researchers are developing a 5 MeV electron linac for radiotherapy applications – part of a national effort to scale technical capacity and capability in medical accelerator technologies.  

Radioisotope collaboration 

Collaboration is hard-wired into PAEC’s operational model and, as such, underpins Pakistan’s radioisotope production programme. PAEC and the International Atomic Energy Agency (IAEA), for example, have been working together in this area for many years and have completed a number of successful technical cooperation projects (with a joint project in the healthcare sector currently under way at the national level). 

CERN is another flagship R&D partner, with PINSTECH and the CERN–MEDICIS facility engaged in a cooperative effort focused on the production and study of innovative radioisotopes for medical diagnostics and treatment. Specifically, the two organisations are carrying out R&D activities on the production of novel medical (reactor- and accelerator-produced) radioisotopes such as ^195mPt, ¹⁶⁵Er, ²²⁵Ac, ¹⁵⁵Tb, ¹⁶¹Tb, ¹⁷⁷Lu – an endeavour, the two partners hope, that will ultimately extend to clinical trials. The bottom line is that Pakistan, which has high cancer mortality and morbidity within its population of 220 million, is keen to take advantage of cutting-edge radioisotope science for the at-scale diagnosis, treatment and management of cancer patients. 

Knowledge transfer 

With this in mind, PINSTECH scientists and engineers have been seconded to the CERN–MEDICIS team for the development of radiochemical activities – including a major contribution to the MEDICIS radiochemistry set-up for the purification of medical radioisotopes with both therapeutic and diagnostic properties (so-called “theranostic” combinations). PINSTECH engineers have also been working on the development of salt/aluminium foils for radio-isotope collection; the management of liquid radioactive waste at MEDICIS; a very promising R&D project relating to the production of ^195mPt for theranostic applications; and the development of a large-scale radiochemistry unit for handling higher levels of radioactivity. 

Fundamental to the PINSTECH-MEDICIS collaboration is the regular exchange of radioisotopes between the two partners. As an example, research quantities of ²²⁵Ac were recently shipped from CERN to Pakistan and, after chemical processing at PINSTECH, transferred to the Lahore-based INMOL cancer clinic (another PAEC facility). Here the ²²⁵Ac was used in the radiolabelling of a targeted “theranostic module” (with the chemical reaction to produce the radiopharmaceutical taking about 30 mins with a yield greater than 95%). 

For Pakistan, opportunity knocks, with the R&D collaboration between PINSTECH and MEDICIS key to the country’s long-term goal of strengthening the technical capability, commercial capacity and production infrastructure to secure a scalable domestic pipeline of novel and high-impact theranostic radioisotopes.

The post Collaboration is key as Pakistan ramps up its radioisotope R&D appeared first on CERN Courier.

The origin story of the IHEP accelerator division can be traced back more than half a century. In 1964, Jialin Xie, the pioneer of Chinese accelerator science and technology, built the country’s first linear accelerator (a 30 MeV electron linac), laying the ground for the development of future large-scale accelerator facilities in China. 

Fast forward to the 1980s and IHEP’s construction of the Beijing Electron–Positron Collider (BEPC) – the foundation of the institute’s own accelerator science programme. Since then, a talented and multidisciplinary accelerator team has grown and developed alongside IHEP’s ambitious research programme in high-energy physics. Today, the IHEP accelerator team is made up of around 370 scientists and engineers, 110 postgraduate students, 26 postdocs and numerous guest scientists working across IHEP’s two campuses in Beijing and Dongguan (an industrial city close to Hong Kong). 

Project management: it’s all about delivery

The IHEP accelerator team works on advanced electron and proton accelerators, with deep domain knowledge and capabilities spanning a broad base of enabling technologies, including (but not limited to) precision mechanics; magnets and power supplies; ultrahigh vacuum components and nonevaporable-getter-(NEG)-coated vacuum chambers; cryogenic systems; superconducting magnets and RF cavities; RF power equipment and accelerating structures; as well as autocontrol systems and cutting-edge instrumentation for beam diagnostics and steering. 

Furthermore, that collective IHEP know-how – tying together fundamental accelerator science, technology innovation and systems engineering – has scaled  dramatically over the past 20 years as the team has overseen the construction and enhancement of several large-scale accelerator initiatives, including: the upgrade of the Beijing Electron–Positron Collider (BEPCII); a high-current proton injector for the Accelerator Driven Sub-critical System (ADS); the China Spallation Neutron Source (CSNS); the High Energy Photon Source (HEPS); as well as formative design work on the proposed 100 km Circular Electron–Positron Collider (CEPC). This is big science at scale – a diverse programme of accelerator R&D that required all manner of technology/engineering innovation along the way:  

1. BEPCII (2004–2009)

BEPCII was a five-year effort to upgrade the original BEPC with a new injector as well as replacing its single-ring collider with a double-ring architecture. Upon completion of the upgrade, BEPCII entered operation in 2009 with an adjustable beam energy in the range 1.0–2.3 GeV and a beam current of 910 mA. Significant progress was registered in terms of the core enabling technologies for a high-beam-current, high-luminosity electron–positron collider, as well as in the design optimisation, system integration and project management. The luminosity of BEPCII reached the design goal of 1 × 10³³ cm^–2.s^–1 at a beam energy of 1.89 GeV (100 times higher than that of BEPC). These successful outcomes informed and shaped subsequent IHEP accelerator projects, including the proposal for the future 100 km CEPC (see below). 

2. ADS (2010–2017)

ADS is a high-power, high-intensity proton machine that has potential applications in nuclear-waste transmutation as well as thorium-based energy production. Under the auspices of the Chinese Academy of Sciences, IHEP developed the world’s first high-frequency, high-power and continuous-wave (CW) proton injector for ADS – the building blocks consisting of a CW radiofrequency quadrupole (RFQ), a superconducting linac, a beam dump and transport lines. The RFQ operates in 325 MHz CW mode, providing a 3.2 MeV acceleration capability, while the superconducting spoke cavities installed in the 2 K cryomodules have successfully accelerated the 10.6 mA proton beam to an energy of 10.67 MeV. As such, ADS is the first proton linac operating at such a high beam current (and integrated by 14 superconducting spoke cavities with a record-breaking beta value of 0.12). 

3. CSNS (2011–2018) 

The CSNS is located on IHEP’s Dongguan campus and consists of an accelerator, a target station and several neutron instruments. The accelerator complex itself is made up of an H^– ion source (with 20 mA current), a four-vane RFQ linac (at 3 MeV), four drift-tube linac tanks (80 MeV), a rapid circling synchrotron (1.6 GeV/25 Hz) and various beam transfer lines. 

CSNS construction was completed in 2018, with the beam power reaching the design value of 100 kW in February 2020. The uncontrolled beam loss rate is less than 1 W/m thanks to IHEP’s custom-designed collimation system and successful mitigation of space-charge effects. Beam availability during 2021/22 operations reached 97.1% (with 5262 hours of effective beam-time on-target). 

The CSNS-II upgrade has since been approved, with construction scheduled to start in 2023. CSNS-II is designed to have a beam power of 500 kW – a capability that will be achieved by adding 20 superconducting double-spoke cavities and 24 six-cell ellipsoidal superconducting cavities to increase the linac beam energy to 300 MeV. Peak current intensity will, in turn, be scaled from 15 mA to 50 mA.

4. HEPS (2019–2025)

HEPS is a fourth-generation synchrotron radiation facility under construction in Huairou, a district in northern Beijing. HEPS consists of a 6 GeV storage ring with a circumference of about 1.3 km, a full energy booster, a 500 MeV linac, three transfer lines, multi-beamlines and corresponding experimental stations. In terms of performance, HEPS aims to have a beam current of 200 mA and a record-breaking ultralow emittance (better than 0.06 nm-rad), promising spectral brightness up to 1 × 10²² phs∙s^-1∙mm^-2∙mrad^-2∙(0.1% BW)^-1 in the typical hard X-ray regime. 

The storage ring consists of 48 hybrid seven-bend acrhomats, with alternating high- and low-beta straight sections to accommodate various types of insertion devices. An innovative and high-energy, accumulation-aided on-axis swap-out scheme is adopted for injection from the booster to the storage ring. In addition, the ultralow-emittance design imposes very-high-precision requirements on all equipment as well as beam diagnostics and controls (with temperature fluctuation in the tunnel also kept within 0.1 °C). 

Worth adding that HEPS will function as a “green accelerator”, with a 10 MW solar power generator (the largest solar power station in Beijing) on the roof of the storage ring serving as a test-case for future machines. 

The HEPS ground-breaking ceremony took place in 2019, with the linac and booster installation now nearing completion. Installation of the storage ring will be completed in 2023, with the first synchrotron X-rays expected in 2024. 

The CEPC blueprint: theory meets technology 

A legacy of successful project delivery and technology innovation on these accelerator initiatives means IHEP physicists are looking ahead to a bright future. Soon after the discovery of the Higgs boson at CERN a decade ago, IHEP scientists unveiled a grand plan to build the CEPC – which will function as a “Higgs factory” – followed by construction of a Super Proton–Proton Collider (SppC) to be housed in the same tunnel. The scope and ambition of these combined facilities would, were they to be realised, unquestionably position IHEP at the cutting-edge of particle physics and accelerator science for decades to come. 

At the same time, fleshing out the design, technology and engineering requirements for a next-generation accelerator complex like the CEPC is, by necessity, a collective endeavour, involving a network of collaborations with scientists and engineers at large-scale research facilities around the world. In terms of high-level design specifications, the circumference of the collider is optimised to be 100 km (based on the construction cost, operational performance and upgrade considerations for the SppC). Meanwhile, the lattice of the CEPC collider ring, as well as the interaction region, are specified so as to achieve high luminosities switchable among various energies corresponding to the Z, W and the Higgs bosons. A number of thorny challenges have already been overcome during the design phase, including beam–beam effects, strong collective instabilities, and radiation background and dose shielding. 

As with all big science initiatives, innovation and cost reduction are ever-present priorities. With this in mind, a number of new technologies are under study – for example, an electron-beam-driven plasma acceleration scheme for the linac injector, as well as the iron-based superconducting coils for the SppC. IHEP is also devoting its efforts to designing the CEPC as a dual-use machine – i.e. a Higgs factory on the one hand, as well as a high-flux, high-energy gamma-ray (up to 100 MeV) synchrotron light source with a multidisciplinary research programme of its own.

CEPC is, by necessity, a collective endeavour, involving a network of collaborations with scientists and engineers at large-scale research facilities around the world

Over the past decade, IHEP and its collaborators have been working on an extensive programme of technology R&D projects as part of the validation and iteration for the CEPC and SppC design studies. Significant progress can be seen along a number of coordinates, including: electropolishing and mid-temperature processing to yield state-of-the-art performance in the 1.3 GHz nine-cell and 650 MHz single-cell superconducting RF cavities; all design specifications met in prototypes of unprecedented low-field dipole and dual-aperture magnets; and prototype energy-efficient klystrons demonstrated an efficiency of 70.5% (closing in on the ultimate target value of 80%). Equally important in this regard is the fact that around 40% of the CEPC hardware requirement will exploit existing platform technologies that are already established at facilities like HEPS, CSNS and BEPCII.

Collaborate and accelerate

One thing is clear: cross-disciplinary and cross-border collaboration are going to be key to translating the technical vision underpinning the CEPC (and the SppC) into scientific reality. In this regard, IHEP is well placed, having a successful track-record of domestic collaboration with accelerator facilities across the country. IHEP scientists and engineers, for example, helped to build the Shanghai Light Source, and collaborated with the Institute of Modern Physics in Lanzhou to build ADS. Cooperation is underway now with the Shanghai Free Electron Laser Facility (to develop and produce superconducting RF cavities) as well as the Dalian Light Source (to build a complete superconducting accelerator module, including cavities and other components). 

It goes without saying that international collaboration is also hard-wired into IHEP’s operational model, with long-term R&D partnerships established in the US (e.g. Brookhaven National Laboratory and SLAC), Europe (CERN and DESY) and Japan (KEK) – and with many of these partners very much to the fore during the construction of BEPC/BEPCII, CSNS, ADS and HEPS. It works both ways, of course, with IHEP recently contributing to CERN’s High Luminosity-LHC upgrade with the provision of 13 units of superconducting corrector magnets. 

As for the future CEPC, the technology R&D effort is being led by IHEP with extensive support from domestic research institutes – including Peking University, Tsinghua University and Shanghai Jiao Tong University – and with additional inputs provided by an Institution Board of 32 universities and research centres. Meanwhile, the CEPC international network comprises an International Advisory Committee (IAC), International Accelerator Review Committee (IARC) and the International Detector R&D Review Committee (IDRDC). The global nature of the collaboration is evident in the CEPC Conceptual Design Report – which has some 1143 authors from 221 research institutes (including 144 overseas institutions across 24 countries) – while the CEPC study group has also signed more than 20 memoranda of understanding with research facilities and universities around the world. 

Wide-scale engagement is everything just now. As such, the CEPC accelerator team has been a participant in the commissioning of KEK’s SuperKEKB electron–positron
collider in Tsukuba, Japan, and has worked with the Future Circular Collider (FCC) team at CERN on fundamental studies of beam–beam interactions and related aspects of beam physics. There’s also been extensive outreach to industry via the CEPC Industry Promotion Consortium (CIPC). Established in 2017, the CIPC now has more than 70 industrial companies participating within China. 

For IHEP’s accelerator division, and its domestic and international partners, a new world of scientific opportunity is rapidly taking shape.

The post IHEP makes the case for accelerator R&D appeared first on CERN Courier.

The FCC-ee, a proposed 91 km future circular collider at CERN foreseen to begin operations in the 2040s, would deliver enormous samples of collision data at a wide range of energies, allowing for ultra-precise studies of the Higgs, W and Z bosons, and the top quark. For example, when running at the Z resonance the FCC-ee will produce – in little more than one minute – a data set the same size as that the LEP collider accumulated in the 1990s during its entire period of operation. For this reason, unlocking the full potential of FCC-ee data will require exquisite systematic control at a level far beyond that achieved at previous colliders.

A beautiful and unique attribute of circular e⁺e^– colliders is that the beams can naturally acquire transverse polarisation, and the precession frequency of the polarisation vector divided by the circulation frequency around the ring is directly proportional to the beam energy. This property allows the energy to be determined with very high precision through applying an oscillating magnetic field which, when in phase with the precession, depolarises the beams. This technique of resonant depolarisation underpins the precise knowledge of the mass and other properties of many particles that now serve as “standard candles”.

A key example is the measurement of the mass and width of the Z boson, and associated electroweak observables, which was the major achievement of the LEP programme. FCC-ee offers the possibility of improving the precision of these measurements by a factor of around 500 – a gigantic advance in precision that will allow for ultra-sensitive tests of the self-consistency of the Standard Model, and provide excellent sensitivity to new heavy particles that may affect the measurements through quantum corrections or mixing. Achieving the best possible knowledge of the collision energy is essential to accomplish this programme, and was the focus of the second FCC Energy Calibration, Polarization and Mono-chromatisation (EPOL) workshop held at CERN from 19 to 30 September, which was a follow-up to the first workshop that took place in 2017.

The two-week workshop was attended by more than 100 accelerator physicists, particle physicists and engineers from around the world; some remote and others participating in person. Presentations focused not only on the challenges at the FCC-ee, but also encompassed activities and initiatives at other facilities. The first week highlighted the plans for polarimetry measurements at the future Electron Ion Collider in the US. Complementary projects were presented from SuperKEKb in Japan, where the accelerator is stress-testing many aspects of the FCC-ee design, CEPC in China and other machines around the world.

Earth tides

The collision-energy calibration is a central consideration in the design and proposed operation strategy of the FCC-ee, in contrast to LEP where it was essentially an afterthought. At LEP, resonant depolarisation measurements were performed in dedicated calibration periods a few times per year. At FCC-ee these measurements will take place continually. This is essential, as a hard-learned lesson from LEP is that the beam energy is not constant, but varies throughout a fill, and also evolves over longer timescales. The gravitational pull of the moon distorts the tunnel in “Earth tides”, and modifies the relative trajectory of the beam through the quadrupole magnets, leading to energy changes that at LEP were around 10 MeV over a few hours during Z running, but will be 20 times larger at FCC-ee. Seasonal changes in the water level of Lac Leman lead to similar effects. At FCC-ee these distortions will be combatted by continuous adjustment of the radio frequency (RF) cavities, as is now routinely done in the LHC.

Additional challenges that were discussed in the workshop included the requirements on the laser polarimeters that will monitor the polarisation levels of the e⁺ and e^– beams, the shifts in collision energy that will occur at each interaction point through the combined effect of synchrotron radiation and the boost provided by the RF system, as well as spurious dispersions folded with collision offsets. Here the project will benefit from the considerable progress achieved since LEP in both the reliability and precision of beam position and dispersion measurements. A particular highlight of the discussions was an agreement that it will be feasible to perform resonant depolarisation measurements at higher energies for use in the determination of the mass of the W boson, which was not possible at LEP, allowing this important parameter of nature to be measured around a factor 20–40 times better than at present.

The workshop concluded with a list of future tasks to be tackled and open questions. These questions will be addressed as part of the ongoing FCC Feasibility Study, with updates planned for the mid-term review, scheduled for the middle of 2023, and the final report in 2025.

The post The power of polarisation for FCC-ee physics appeared first on CERN Courier.

The HL-LHC aims to operate with 2.3 × 10¹¹ protons per bunch (compared to the goal of 1.8 × 10¹¹ protons per bunch at the end of Run 3), producing a stored beam energy of about 710 MJ (compared to 540 MJ in Run 3). Lead–ion beams, on the other hand, will already reach their HL-LHC target intensity upgrade in Run 3. This is thanks to the “slip stacking” technique currently implemented at the Super Proton Synchrotron, which uses complex radio-frequency manipulations to shorten the bunch spacing of LHC beam trains from 75 to 50 ns. Equating to a stored beam energy of up to 20.5 MJ at 6.8 TeV (compared to a maximum of 12.9 MJ achieved in 2018 at 6.37 TeV), the full HL-LHC upgrade needed to handle these more intense ion beams must be available throughout Run 3.

When the LHC works as a heavy-ion collider, many specific challenges need to be faced. Magnetically, the machine behaves in a similar way as during proton–proton operation. However, since the lead–ion bunch charge is about 15 times lower than for protons, a number of typical machine challenges – such as beam–beam interactions, impedance, electron-cloud effects, injection and beam-dump protection – are relaxed. Mitigating the nuisance of beam halos, however, is certainly not one of the tasks that gets easier. 

These halos are formed by particles that stray from the ideal beam orbit. More than 100 collimators are located at specific locations in the LHC to ensure that errant particles are cleaned or absorbed, thus protecting sensitive superconducting and other accelerator components. Although the total stored beam energy with ions is more than 30 times lower than it is for protons, the conventional multi-stage collimation system at the LHC (see “Multi-stage collimation” figure) is about two orders of magnitude less efficient for ion beams. Nuclear fragmentation processes occurring when ions interact with conventional collimator materials produce ion fragments with different magnetic rigidities without producing transverse kicks sufficient to steer these fragments onto the secondary collimators. Instead, they travel nearly unperturbed through the “betatron” collimation system in interaction region 7 (IR7) responsible for disposing safely of transverse beam losses. This creates clusters of losses in the high-dispersion regions, where the first superconducting dipole magnets of the cold arcs act as powerful spectrometers, increasing the risk of quenches whereby the magnets cease to become superconducting. 

The ion-collimation limitation is a well-known concern for the LHC. Nevertheless, the standard system has performed quite well so far and provided adequate cleaning efficiency for the nominal LHC ion-beam parameters. But the HL-LHC targets pose additional challenges. In particular, the upgrade does not allow sufficient operational margins without improving the betatron collimation cleaning. Lead–ion beam losses in the cold dipole magnets downstream of IR7 might reach a level three times higher than their quench limits, estimated at their 7 TeV current equivalent.

Various paths have been followed within the HL-LHC project to address this limitation. The baseline solution was to improve the collimation cleaning by adding standard collimators in the dispersion-suppressor regions that would locally dispose of the off-momentum halo particles before they impact the cold magnets. To create the necessary space, two shorter dipoles with a stronger (11 T) field would replace a standard, 15 m-long 8.3 T LHC dipole. This robust upgrade, which works equally well for proton beams, was planned to be used in Run 3. However, due to technical issues with the availability of the new dipoles, which are based on a niobium-tin rather than niobium-titanium conductor, the decision was taken to defer their installation. The HL-LHC project now relies on an alternative solution based on a crystal collimation scheme that was studied in parallel.

Crystals in the LHC

The development of crystal applications with hadron beams at CERN dates back to the activities carried out by the UA9 collaboration at the CERN SPS. Crystal collimation makes use of a phenomenon called planar channelling: charged particles impinging on a pure crystal with well-defined impact conditions can remain trapped in the electromagnetic potential well generated by the regular planes of atoms. If the crystal is bent, particles follow its geometrical shape and experience a net kick that can steer them with high efficiency to a downstream absorber. Crystal collimation was tested at the Tevatron, and in 2018 a prototype system was used for protons at the LHC in a special run at injection energy. The scheme is particularly attractive for ion beams as it was demonstrated that the existing secondary collimators can serve as a halo absorber without risking damage. 

At the LHC, a total of four bent crystals are needed for the horizontal and vertical collimation of both beams. During Run 2, a test stand for crystal-collimation tests was installed in the LHC betatron cleaning region of IR7 with the aim of demonstrating the feasibility of this advanced collimation technique at LHC energies. Silicon crystals with a length of just 4 mm were bent to a curvature radius of 80 m to produce a 50 μrad deflection – much larger than the few-μrad angles typically experienced by proton interaction with the 60 cm-long primary collimators (see “Silicon swerve” image). Indeed, to produce such a kick with conventional dipole magnets would require a field of around 300 T in the same volume of the crystal. The crystals were mounted on an assembly (see “On target” image) that is a jewel of accelerator technology and control: the target collimator primary crystal (TCPC). This device allows the crystal to be moved to the desired distance from the circulating beam – typically just a few millimetres at 7 TeV – and its angular orientation to be adjusted to better than 1 μrad. While the former is no more demanding than the control system of other LHC collimators, the angular control demands a customised technology that is the heart of LHC crystal collimation. 

Crystal channelling can only occur for particles impinging on the crystal surface with well-defined impact conditions. For a 6.8 TeV proton beam, they must have an angle of 90° with angular deviations of at most ±0.0001° (around ±2 μrad) – which is similar to aiming at a 10 cm-wide snooker pocket from a shooting distance of 25 km! If this tiny angular acceptance is not respected, the transverse momentum is sufficient to send particles out of the potential well produced between the planes of the crystal lattice, thus losing the channelling condition. Both the beam-impact conditions and the accuracy of the crystal’s angle must therefore be kept under excellent control. 

The crystal collimators are steered remotely using a technology that is unique to the CERN accelerator complex. It relies on a high-precision interferometer that provides suitable feedback to the advanced controller, and a precise piezo-actuation device that drives the crystal orientation with respect to impinging halo particles with unprecedented precision. During Run 2, the system demonstrated the sub-microradian accuracy required to maintain crystal channelling at high beam energy (see “High precision” figure, top). A recent feature of the newly installed devices is that the interferometer heads (which enable the precise control of the angle) are located outside the vacuum with the laser light coupled to the angular stage by means of viewports. This means that any fibre degradation due to motion or radiation, which was observed on the prototype system, can be corrected during routine maintenance. Using this setup in 2018, an improvement in ion-collimation cleaning by up to a factor of eight was demonstrated experimentally with the best crystal, paving the way for crystal collimation to become the baseline solution for the HL-LHC. 

The test devices used during Run 2 served their purpose well, but they do not meet the standards required for regular, high-efficiency operation. An upgrade plan was therefore put in place to replace them with a higher performing new design. This has been developed in a crash programme at CERN that started in November 2020, when the decision to postpone the installation of the 11 T dipoles was taken. Two units were built and installed in the LHC in 2021 (see “On target” image) and another four are nearing completion: two for installation in the LHC at the end of 2022 and the others serving as operational spares. The first two installed units replaced the two prototype vertical crystals that showed the lowest performance. The horizontal prototype devices remain in place for 2022, since they performed well and were tested with a pilot beam in October 2021. 

Improved ion-collimation cleaning has paved the way to adopt crystal collimation as the baseline of the HL-LHC

The start of Run 3 in April this year provided a unique opportunity to test the new devices with proton beams, ahead of the next operational ion run. One of the first challenges is to establish the optimal alignment of the crystals, to make sure stray particles are channelled as required. While channelled, the impinging particles interact with the crystal with the lowest nuclear-interaction rate: halo particles travel preferentially in the “empty” channel relatively far from the lattice nuclei. Optimum channelling is therefore revealed by the orientation that has the lowest losses, as measured by beam-loss monitors located immediately downstream of the crystal (see “High precision” figure, bottom). Considering the large angular range possible (more than 50 μrad, compared with the full angular range of 20 mrad), establishing this optimum condition is a bit like finding a needle in a haystack. However, following a successful campaign in dedicated operational beam tests in August 2022, channelling was efficiently established for both the new and old crystals, allowing the commissioning phase to continue. 

Looking forward

The LHC collimation system is the most complex beam-cleaning system built to date for particle accelerators. However, it must be further improved to successfully face the upcoming challenges from the HL-LHC upgrade which, for heavy-ion beams, begins during Run 3. Crystal collimation is a crucial upgrade that is now being put into operation to improve the betatron cleaning in preparation for the upgraded ion-beam parameters, mitigating the risks of machine downtime from ion-beam losses. The collimation cleaning performance will be established experimentally as soon as Run 3 ion operation begins. Initial beam tests with protons indicate that the newly installed bent crystals perform well. The first measurements demonstrated that the crystals can be put into operation as expected and showed the specified channelling property. We are therefore confident that this advanced technology can be used successfully for the heavy-ion challenges of the HL-LHC programme.

The post Crystal collimation brings HL-LHC into focus appeared first on CERN Courier.

In school I liked and did well in science and math. I liked the feeling of certainty of math. There is an objective truth in math. And I was fascinated by the fact that I could use math to describe physical phenomena, to capture the complexity of the world in elegant mathematical equations. I also had an excellent, rigorous high-school physics teacher, whom I admired. 

Accelerators offered the possibility of addressing fundamental challenges in (accelerator) physics and technology, and getting verifiable results in a reasonable amount of time to have a material impact. In addition, particle accelerators enable research and discovery in a vast range of scientific fields (such as particle and nuclear physics, X-ray and neutron science) and societal applications such as cancer treatment and radioisotope production.

What was your thesis topic? 

My PhD thesis tackled experimentally, theoretically and via computer simulations the nonlinear dynamics of transverse particle oscillations in the former Tevatron collider at Fermilab, motivated by planning for the Superconducting Super Collider. Nonlinearities were introduced in the Tevatron by special sextupole magnets. In a series of experiments, we obtained accurate measurements of various phase–space features with sextupoles switched on. One of the features was the experimental demonstration of “nonlinear resonance islands” – protons captured on fixed points in phase space.

What have been the most rewarding and challenging aspects of your career so far?

There are many rewarding aspects of what I do. Seeing an audience, especially young people, who light up when I explain a fascinating concept. Pointing to something tangible that I contributed towards that will enable scientists to make discoveries in accelerator, particle or nuclear physics. Having conceived, worked on and advocated certain types of accelerators and seeing them realised. Predicting a behaviour of the particle beam, and verifying it in experiments. Also, troubleshooting a serious problem, and after days and nights of toil, finding the origin of or solution to the problem. 

In terms of challenges, at Fermilab right now we are working on very complex and challenging projects like LBNF/DUNE. It involves more than 1400 international collaborators preparing and building a technically complex endeavour almost one mile underground. The mere scale of the operation is enormous but the pay-off is completing something unprecedented and enabling groundbreaking discoveries.

What are your goals as Fermilab director?

First and foremost, the completion of LBNF/DUNE to advance neutrino physics. Also, the completion of the remainder of the 2014 “P5” programmes, including the HL-LHC upgrades of the accelerator and CMS detector, and a new experiment at Fermilab called Mu2e. Looking to the future, when the next P5 report is completed, we will launch the next series of projects. Quantum technology is also a growing focus. Fermilab hosts one of five national quantum centres in addition to being a partner in a second one. We utilise our world-leading expertise in superconducting radiofrequency technology and instrumentation/control to advance quantum information technologies, as well as conducting unique dark-matter searches using this expertise. 

Is being director different to what you imaged?

It takes a lot of hard work to build an excellent team, exceeding my initial projection. But equally our staff’s commitment, good will and dedication have also exceeded my expectations.

Which collider should follow the LHC, and what is the role of the US/Fermilab in realising such a project? 

No matter which collider is chosen, there is still a lot of R&D required for any path concerning magnets, radiofrequency cavities and detectors. This R&D is crucial to multiple applications. I would advocate the development of these capabilities to push the state of the art for accelerators and detectors in the near future. Future colliders are an important component of the current Snowmass/P5 community planning exercise. Here, Fermilab is aligned with the previous P5 and is committed to following the next P5 recommendations.

How would you describe high-energy physics today compared to when you entered the field?

In the 1980s, the major building blocks of the Standard Model were largely in place, and the focus of the field was to experimentally verify many of its predictions. Today, the Standard Model is much more thoroughly tested, but there is evidence that it does not completely describe the whole picture. 

The upcoming century promises a fascinating array of ground-breaking discoveries

A lot of present-day research is about physics beyond the Standard Model, including dark matter, dark energy and the question of matter–antimatter asymmetry in the universe. In parallel, technologies have advanced tremendously since the 1980s, enabling unprecedented precision, parameter reach and new discoveries. This applies to accelerators, telescopes, detectors and computing. The upcoming century promises a fascinating array of groundbreaking discoveries, all of which will fundamentally further our understanding of the universe. 

What can be done to ensure that there are more female laboratory directors worldwide?

I think it is important to increase the pipeline, starting with efforts to attract young people in elementary and high school. We need to look at changing the cultural perspective that women can’t do STEM and get to the point where the entire culture is open-minded. We also need to change the make-up of the committees. 

It is important to encourage females to take on leadership positions and then support and empower them with enlightened mentors. Once they develop their careers, we will have a much bigger pool for future lab directors. We must inspire and empower young girls and women to follow their dreams, and help them stay focused to succeed. 

The post A view from Fermilab appeared first on CERN Courier.

Maximising energy efficiency is a major factor in the FCC design. Two new projects backed by the Swiss Accelerator Research and Technology collaboration (CHART) seek to reduce the environmental impact of FCC-ee by exploring the use of high-temperature superconductors in core accelerator technologies. 

Much like its predecessor, LEP, and indeed every lepton collider to date, the main magnet systems in the FCC-ee design are based on normal-conducting technology. While perfectly adequate from a magnetic-field point of view, normal-conducting magnets consume electricity through Ohmic heating. The FCC-ee focusing and defocusing elements, comprising about 3000 quadrupole magnets and 6000 sextupole magnets, are estimated to consume in excess of 50 MW when operating at the highest energies. This can be reduced if the magnetic systems are made superconducting, and if high-temperature superconductors (HTS) were to be used. Whereas conventional superconductors such as the niobium-titanium used in the LHC must be cooled to extremely low temperatures (1.9–4.5 K), state-of-the-art HTS materials can operate up to 90 K, significantly reducing the cryogenic power needed to keep them superconducting. The question remains if high-performing HTS accelerator magnets, with all their advantages on paper, can be built in practice.

Turning FCC-ee superconducting not only helps with operational costs and environmental credentials, but the new HTS technology has potential applications in everyday life

In April 2022, the CHART executive board gave the green light to two projects investigating the feasibility of superconducting technology for the main magnet systems of FCC-ee. CHART was founded in 2016 as an umbrella collaboration for R&D activities in Switzerland, with CERN, PSI, EPFL, ETH-Zurich and the University of Geneva as present partners. The larger HTS4 project, involving CERN and PSI, will focus on superconducting magnets, while CPES (Cryogenic Power Electronic Supply) will focus on cryogenic power supplies, with partners ETHZ and PSI.

The use of HTS-based magnets could dramatically reduce the power drawn by the main quadrupole and sextupole systems for FCC-ee when operating at the highest centre-of-mass energies, explains HTS4 principal investigator Michael Koratzinos of PSI. Furthermore, he says, since HTS magnets do not need iron to shape the magnetic field, they can be made much lighter and can be nested inside one another to increase performance and flexibility in the optics design. “Turning FCC-ee superconducting not only helps with the reduction in operational costs and the environmental credentials of the accelerator, but it also helps society develop this new and exciting HTS technology with potential applications in everyday life.”

High demand

HTS conductors are currently in high demand, mainly from a multitude of privately-funded fusion projects, such as the SPARC project at MIT. Their main disadvantage is their high cost, but this is expected to come down as demand picks up. SPARC needs about 10,000 km of HTS conductor during the next few years, compared to an estimated 20,000 km for FCC-ee, although on a later time scale. 

The ultimate aim of HTS4 is the production of a full-size prototype of one of the FCC-ee short-straight sections based on HTS technology. Four work packages will address: integration with the rest of the FCC-ee accelerator systems; enabling technologies on peripheral issues such as impregnation; the conceptual and technical design of a short demonstrator and a prototype; and the design, construction and testing of the full prototype module.

“Any future project at CERN and elsewhere relies on innovative R&D to minimise its electricity consumption,” says project leader of the FCC study Michael Benedikt of CERN. “We are doing our utmost at FCC to increase our energy efficiency.” 

The post FCC-ee designers turn up the heat appeared first on CERN Courier.

Following final pitches in the Globe by the four shortlisted entrants, a consortium led by Swiss firm BG Ingenieurs Conseils was awarded first prize – including support to the value of €40,000 to bring the technology to maturity – for their proposal “Molasse is the New Ore”. Using a near real-time flow analysis that has been demonstrated in cement plants, the proposal would see excavated materials immediately identified and separated for further processing on-site, treating them not as waste that needs to be managed and thereby serving environmental objectives and efficiency targets. 

The runners-up were proposals led by: Amberg (to sort, characterise and redistribute the molasse into fractions of known compositions and recycle each material on a large scale locally); Briques Technique Concept (to produce bricks from the excavated material for the construction of nearby buildings); and Edaphos (to process the molasses into topsoil-like material in a process known as soil conditioning). Although only one winner was chosen, it emerged during the ceremony that an integrated approach of all four shortlisted scenarios would be a valid scenario for managing the estimated 7–8 million m³ of molasse materials required for the FCC construction project. 

“This is a key ingredient for the FCC feasibility study while also creating business opportunities for applying these technologies in different markets,” said competition creator Johannes Gutleber of CERN. “The proposals submitted in the course of the contest show that designing a new research infrastructure acts as an amplifier of ideas for society at large.”

The post Sustainable mining wins awards appeared first on CERN Courier.

After five years of arduous and continuous activity, the main civil-engineering works for the High-Luminosity LHC project (HL–LHC) are on track to be completed by the end of the year. Approved in June 2016 and due to enter operation in 2029, the HL-LHC is a major upgrade that will extend the LHC’s discovery potential significantly. It relies on several innovative and challenging technologies, including new superconducting quadrupole magnets, compact crab cavities to rotate the beams at the collision points, and 80 m-long high-power superconducting links, among many others.

These new LHC accelerator components will be mostly integrated at Point 1 and Point 5 of the ring, where the two general-purpose detectors ATLAS and CMS are located, respectively. As such, the HL-LHC requires new, large civil-engineering structures at each site to house the services, technical infrastructure and accelerator equipment required to power, control and cool the machine’s new long-straight sections.

Connections

At each Point, the underground structures consist of a vertical shaft (80 m deep and 10 m in diameter) leading to a service cavern (16 m in diameter and 46 m long). A power-converter gallery (5.6 m in diameter and 300 m long), two service galleries (3.1 m in diameter and 54 m long), two radio-frequency galleries (5.8 m in diameter and 68 m long), as well as two short safety galleries, complete the underground layout. The connection to the LHC tunnel will be made via 12 vertical cores (1 m in diameter and 7 m deep), which will be drilled later and completed during long-shutdown 3 after the removal of the existing LHC long-straight sections.

The two sites generated 120 jobs on average from 2018 to 2021, solely for companies in charge of civil-engineering construction

Luz Anastasia Lopez-Hernandez

The surface structures consist of five buildings. Three are constructed from reinforced concrete to house noisy equipment such as helium compressors, cooling towers, water pumps, chillers and ventilation units. The other two buildings have steel-frame structures to house electrical distribution cabinets, a helium refrigerator cold-box and the shaft access system. The buildings are interconnected via buried technical galleries.

The HL-LHC civil-engineering project is based on four main contracts. Two consultancy service contracts are dedicated to the design and construction administration: Setectpi-CSD-Rocksoil (ORIGIN) at Point 1 and Lombardi-Artelia-Pini (LAP) at Point 5. Two supply contracts are dedicated to the construction of both the underground and surface structures: Marti Tunnelbau – Marti Österreich – Marti Deutschland (JVMM) at Point 1 and Implenia Schweiz – Baresel – Implenia Construction (CIB) at Point 5.

In total, 92,000 m³ of spoil has been excavated from the underground structures, while 30,000 m³ of concrete and 5000 tonnes of reinforcement-steel were used to construct the underground structures. At Point 5, based on the experience of civil engineering for the CMS shaft, groundwater infiltration was envisaged to make HL-LHC shaft excavation difficult. A different execution methodology and a dry summer in 2018 made the task easier, although the discovery of unexpected hydrocarbon layers (not seen during the CMS works) added some additional difficulties in the management of the polluted spoil. At Point 1, the expected quantity of spoil polluted by hydrocarbon was managed accordingly. The construction of the surface structures, meanwhile, required 6 km of anchor piles, 15,000 m³ of concrete, 1400 tonnes of reinforcement-steel and 700 tonnes of steel frames.

Opportunities

“The two sites generated 120 jobs on average from 2018 to 2021, solely for companies in charge of civil-engineering construction,” says Luz Anastasia Lopez-Hernandez, head of the project-portfolio management group of the site and civil-engineering department.

Special care was taken to limit worksite nuisance with respect to CERN’s neighbours. Truck wheels were systematically washed before leaving the worksites, and temporary buildings were erected on top of the shaft heads to limit the noise impact of the excavation work. The only complaint received during the construction period was related to light pollution at Point 5, after which it was decided to limit worksite lighting during nightfall to the minimum compatible with worker safety. As the excavation of the two shafts started in 2018 in parallel with LHC operation, special care was taken to limit the vibration level by using electrically driven road-header excavators.

The COVID-19 pandemic, which, among other things, required the two worksites to be closed for several weeks in 2020, caused a delay of one-to-two months with respect to the initial construction schedule. The Russian Federation’s invasion of Ukraine also impacted activities this year by delaying some deliveries.

“The next step is to equip these new structures with their technical infrastructures before the next long shutdown, which will be dedicated to the installation of the accelerator equipment,” says Laurent Tavian, work-package leader of the HL–LHC infrastructure, logistics and civil engineering.

The post HL–LHC civil engineering reaches completion appeared first on CERN Courier.

The 13th International Particle Accelerator Conference (IPAC’22), which took place in Bangkok from 12 to 17 June, marked the return of an in-person event after two years due to the COVID pandemic. Hosted by the Synchrotron Light Research Institute, it was the first time that Thailand has hosted an IPAC conference, with around 800 scientists, engineers, technicians, students and industrial partners from 37 countries in attendance. The atmosphere was understandably electric. Energy and enthusiasm filled the rooms, as delegates had the chance to meet with colleagues and friends from around the world.

The conference began with a blessing from princess Maha Chakri Sirindhorn, who attended the two opening plenary sessions. The scientific programme included excellent invited and contributed talks, as well as outstanding posters, highlighting scientific achievements worldwide. Among them were the precise measurement of the muon’s anomalous magnetic dipole moment (g-2) at Fermi­lab, and the analysis at synchrotron light sources of soil samples obtained from near-Earth asteroid 162173 Ryugu by the Hayabusa2 space mission, which gave a glimpse into the origin of the Solar System.

In total, 88 invited and contributing talks on a wide array of particle accelerator-related topics were presented. These covered updates of new collider projects such as the Electron Ion Collider (EIC), proposed colliders (FCC, ILC and CEPC), as well as upgrade plans for existing facilities such as BEPCII and SuperKEKB, and new photo-source projects such as NanoTerasu and Siam Photon Source II. A talk about the power efficiency of accelerators drew a lot of attention given increasing global concern about sustainability. Accelerator-based radiotherapy continued to be the main topic in the accelerator application category, with a special focus on designing an affordable and low-maintenance linac for deployment in low- and middle-income countries and other challenging environments (CERN Courier January/February 2022 p30). 

Raffaella Geometrante (KYMA) hosted a popular industry session on accelerator technology. Completely revamped from past editions, its aim was to substantially improve the dynamics between laboratories and industry, while also addressing other topics on accelerator innovations and disruptive technologies. 

An engaging outreach talk “Looking into the past with photons” highlighted how synchrotron radiation has become an indispensable tool in archaeological and paleontological research, enabling investigations of the relationship between past civilisations in different corners of the world. A reception held during an evening boat cruise along the Chao Phraya River took participants past majestic palaces and historic temples against a backdrop of traditional Thai music and performances.

IPAC’22 was a successful and memorable conference, seen as a symbol of our return to normal scientific activities and face-to-face interaction. It was also one of the most difficult IPAC conferences to organise – prohibiting or impeding participation from several regions, particularly China and Taiwan, as the world begins to recover from the most prevalent health-related crisis in a century. It was mentioned in the opening session that many breakthroughs in combating the coronavirus pandemic were achieved with the use of particle accelerators: the molecular structure of the virus, which is essential information for subsequent rational drug design, was solved at synchrotron light sources.

The post IPAC back in full force appeared first on CERN Courier.

More than 500 participants from over 30 countries attended the annual meeting of the Future Circular Collider (FCC) collaboration, which is pursuing a feasibility study for a visionary post-LHC research infrastructure at CERN. Organised as a hybrid event at Sorbonne University in Paris from 30 May to 3 June, the event demonstrated the significant recent progress en route to the completion of the feasibility study in 2025, and the technological and scientific opportunities on offer.

In their welcome talks, Ursula Bassler (CNRS) and Philippe Chomaz (CEA), chair of the FCC collaboration board, stressed France’s long-standing participation in CERN and reaffirmed the support of French physicists and laboratories in the different areas of the FCC project. CERN Director-General Fabiola Gianotti noted that the electron–positron stage, FCC-ee, could begin operations within a few years of the end of the HL-LHC – a crucial step in keeping the community engaged across different generations – while the full FCC programme would offer 100 years of trailblazing physics at both the energy and intensity frontiers. Beyond its outstanding scientific case, FCC requires coordinated R&D in many domains, such as instrumentation and engineering, raising opportunities for young generations to contribute with fresh ideas. These messages echoed those in other opening talks, in particular by Jean-Eric Paquet, director for research and innovation at the European Commission, who highlighted FCC’s role as a world-scale research infrastructure that will allow Europe to maintain its leadership in fundamental research.

A new era

Ten years after the discovery of the Higgs boson, the ATLAS and CMS collaborations continue to establish its properties and interactions with other particles. The discovery of the Higgs boson completes the Standard Model but leaves many questions unanswered; a new era of exploration has opened that requires a blend of large leaps in precision, sensitivity and eventually energy. Theorist Christophe Grojean (DESY) described how the diverse FCC research programme (CERN Courier May/June 2022 p23) offers an extensive set of measurements at the electroweak scale, the widest exploratory potential for new physics, and the potential to address outstanding questions such as the nature of dark matter and the origin of the cosmic matter–antimatter asymmetry.

In recent months, teams from CERN have worked closely with external consultants and CERN’s host states to develop a new FCC layout and placement scenario (CERN Courier May/June 2022 p27). Key elements include the effective use of the European electricity grid, the launch of heat-recovery projects, cooling, agriculture and industrial use – as well as cutting-edge data connections to rural areas. Parallel sessions at FCC Week focused on the design of FCC-ee, which offers a high-luminosity Higgs and electroweak factory. Tor Raubenheimer (SLAC) showed it to be the most efficient lepton collider for energies up to the top-quark mass threshold and highlighted its complementarity to a future FCC-hh. Profiting from the FCC-ee’s high technological readiness, ongoing R&D efforts aim to maximise the efficiency and performance while optimising its environmental impact and operational costs. Many sessions were dedicated to detector development, where the breadth of new results showed that the FCC-ee is much more than a scaled-up version of LEP. It would offer unprecedented precision on Higgs couplings, electroweak and flavour variables, the top-quark mass, and the strong coupling constant, with ample discovery potential for feebly interacting particles. Participants also heard about the FCC-ee’s unique ability in ultra-precise centre-of-mass energy measurements, and the need for new beam-stabilisation and feedback systems.

The FCC programme builds on the large, stable global community that has existed for more than 30 years at CERN and in other laboratories worldwide

High-temperature superconductor (HTS) magnets are among key FCC-ee technologies under consideration for improved energy efficiency, also offering significant potential societal impact. They could be deployed in the FCC-ee final-focus sections, around the positron-production target, and even in the collider arcs. Another major focus is ensuring that the 92 km-circumference machine’s arc cells are effective, reliable and easy to maintain, with a complete arc half-cell mockup planned to be constructed by 2025. The exploration of existing and alternative technologies for FCC-ee is supported by two recently approved projects: the Swiss accelerator R&D programme CHART, and the EU-funded FCCIS design study. The online software requirements for FCC-ee are dominated by an expected physics event rate of ~200 kHz when running at the Z pole. Trigger and data acquisition systems sustaining comparable data rates are already being developed for the HL-LHC, serving as powerful starting points for FCC-ee.

Looking to the future

Finally, participants reviewed ongoing activities toward FCC-hh, an energy- frontier 100 TeV proton–proton collider to follow FCC-ee by exploiting the same infrastructure. FCC-hh studies complement those for FCC-ee, including the organisation of CERN’s high-field magnet R&D programme and the work of the FCC global conductor-development programme. In addition, alternative HTS technologies that could reach higher magnetic fields and higher energies while reducing energy consumption are being explored for FCC’s energy-frontier stage. The challenges of building and operating this new infrastructure and the benefits that can be expected for society and European industry were also discussed during a public event under the auspices of the French Physical Society. 

The FCC programme builds on the large, stable global community that has existed for more than 30 years at CERN and in other laboratories worldwide. The results presented during FCC Week 2022 and ongoing R&D activities will inspire generations of students to learn and grow. Participants from diverse fields and the high number of junior researchers who joined the meeting underline the attractiveness of the project. Robust international participation and long-term commitment to deliver ambitious projects are key for the next steps in the FCC feasibility study.

The post A word from FCC Week appeared first on CERN Courier.

The radio-frequency (RF) cavities that accelerate charged particles in machines like the LHC are powered by devices called klystrons. These electro-vacuum tubes, which amplify RF signals by converting an initial velocity modulation of a stream of electrons into an intensity modulation, produce RF power in a wide frequency range (from several hundred MHz to tens of GHz) and can be used in pulsed or continuous-wave mode to deliver RF power from hundreds of kW to hundreds of MW. The close connection between klystron performance and the power consumption of an accelerator has driven researchers at CERN to develop more efficient devices for current and future colliders. 

The efficiency of a klystron is calculated as the ratio between generated RF power and the electrical power that is delivered from the grid. Experience with many thousands of such devices during the past seven decades has established that at low frequency and moderate RF power levels (as required by the LHC), klystrons can deliver an efficiency of 60–65%. For pulsed, high-frequency and high peak-RF power devices, efficiencies are about 40–45%. The efficiency of RF power production is a key element of an accelerator’s overall efficiency. Taking the proposed future electron–positron collider FCC-ee as an example: by increasing klystron efficiency from 65 to 80%, the electrical power savings over a 10-year period could be as much as 1 TWhr. In addition, reduced demand on the electrical power storage capacity and cooling and ventilation may further reduce the original investment cost.

In 2013 the development of high-efficiency klystrons started at CERN within the Compact Linear Collider study as a means to reduce the global energy consumed by the proposed collider. Thanks to strong support by management, this evolved into a project inside the CERN RF group. A small team of five people at CERN and Lancaster University, led by Igor Syratchev, developed accurate computer tools for klystron simulations and in-depth analysis of the beam dynamics, and used them to evaluate effects that limit klystron efficiency. Finally, the team proposed novel technological solutions (including new bunching methods and higher order harmonic cavities) that can improve klystron efficiency by 10–30% compared to commercial analogues. These new technologies were applied to develop new high-efficiency klystrons for use in the high-luminosity LHC (HL-LHC), FCC-ee and the CERN X-band high-gradient facilities, as well as in medical and industrial accelerators. Some of the new tube designs are now undergoing prototyping in close collaboration between CERN and industry.

The first commercial prototype of a high-efficiency 8 MW X-band klystron developed at CERN was built and tested by Canon Electron Tubes and Devices in July this year. Delivering an expected power level with an efficiency of 53.3% measured at their factory in Japan, it is the first demonstration of the technological solution developed at CERN that showed an efficiency increase of more than 10% compared to commercially available devices. In terms of RF power production, this translates to an overall increase of 25% using the same wall-plug power as the model currently working at CERN’s X-band facility. Later this year the klystron will arrive at CERN and replace Canon’s conventional 6 MW tube. The next project in progress aims to fabricate a high-efficiency version of the LHC klystron, which, if successful, could be used in the HL-LHC.

“These results give us confidence for the coming high-efficiency version of the LHC klystrons and for the development of FCC-ee,” says RF group leader Frank Gerigk. “It is also an excellent demonstration of the powerful collaboration between CERN and industry.” 

The post CERN and Canon demonstrate efficient klystron appeared first on CERN Courier.

A multidisciplinary team in the UK has received seed funding to investigate the feasibility of a new facility for ion-therapy research based on novel accelerator, instrumentation and computing technologies. At the core of the facility would be a laser-hybrid accelerator dubbed LhARA: a high-power pulsed laser striking a thin foil target would create a large flux of protons or ions, which are captured using strong-focusing electron–plasma lenses and then accelerated rapidly in a fixed-field alternating-gradient accelerator. Such a device, says the team, offers enormous clinical potential by providing more flexible, compact and cost-effective multi-ion sources.

High-energy X-rays are by far the most common radiotherapy tool, but recent decades have seen a growth in particle-beam radiotherapy. In contrast to X-rays, protons and ion beams can be manipulated to deliver radiation doses more precisely than conventional radiotherapy, sparing surrounding healthy tissue. Unfortunately, the number of ion treatment facilities is few because they require large synchrotrons to accelerate the ions. The Proton-Ion Medical Machine Study undertaken at CERN during the late 1990s, for example, underpinned the CNAO (Italy) and MedAustron (Austria) treatment centres that helped propel Europe to the forefront of the field – work that is now being continued by CERN’s Next Ion Medical Machine Study (CERN Courier July/August 2021 p23).

“LhARA will greatly accelerate our understanding of how protons and ions interact and are effective in killing cancer cells, while simultaneously giving us experience in running a novel beam,” says LhARA biological science programme manager Jason Parsons of the University of Liverpool. “Together, the technology and the science will help us make a big step forward in optimising radiotherapy treatments for cancer patients.” 

A small number of laboratories in Europe already work on laser-driven sources for biomedical applications. The LhARA collaboration, which comprises physicists, biologists, clinicians and engineers, aims to build on this work to demonstrate the feasibility of capturing and manipulating the flux created in the laser-target interaction to provide a beam that can be accelerated rapidly to the desired energy. The laser-driven source offers the opportunity to capture intense, nanosecond-long pulses of protons and ions at an energy of 15 MeV, says the team. This is two orders of magnitude greater than in conventional sources, allowing the space-charge limit on the instantaneous dose to be evaded. 

In July, UK Research and Innovation granted £2 million over the next two years to deliver a conceptual design report for an Ion Therapy Research Facility (ITRF) centred around LhARA. The first goal is to demonstrate the feasibility of the laser-hybrid approach in a facility dedicated to biological research, after which the team will work with national and international partnerships to develop the clinical technique. While the programme carries significant technical risk, says LhARA co-spokesperson Kenneth Long from Imperial College London/STFC, it is justified by the high level of potential reward: “The multi­disciplinary approach of the LhARA collaboration will place the ITRF at the forefront of the field, partnering with industry to pave the way for significantly enhanced access to state-of-the-art particle-beam therapy.” 

The post Exploring a laser-hybrid accelerator for radiotherapy appeared first on CERN Courier.

An ambitious upgrade of the US’s flagship X-ray free-electron-laser facility – the Linac Coherent Light Source (LCLS) at SLAC in California – is nearing completion. Set for “first light” early next year, LCLS-II will deliver X-ray laser beams that are 10,000 times brighter than LCLS at repetition rates of up to a million pulses per second – generating more X-ray pulses in just a few hours than the current laser has delivered through the course of its 12-year operational lifetime. The cutting-edge physics of the new facility – underpinned by a cryogenically cooled superconducting radio-frequency (SRF) linac – will enable the two beams from LCLS and LCLS-II to work in tandem. This, in turn, will help researchers observe rare events that happen during chemical reactions and study delicate biological molecules at the atomic scale in their natural environments, as well as potentially shed light on exotic quantum phenomena with applications in next-generation quantum computing and communications systems. 

Successful delivery of the LCLS-II linac was possible thanks to a multi-centre collaborative effort involving US national and university laboratories, following the decision to pursue an SRF-based machine in 2014 through the design, assembly, test, transportation and installation of a string of 37 SRF cryomodules (most of them more than 12 m long) into the SLAC tunnel. All told, this major undertaking necessitated the construction of forty 1.3 GHz SRF cryomodules (five of them spares) and three 3.9 GHz cryomodules (one spare) – with delivery of approximately one cryomodule per month from February 2019 until December 2020 to allow completion of the LCLS-II linac installation on schedule by November 2021. 

This industrial-scale programme of works was shaped by a strategic commitment, early on in the LCLS-II design phase, to transfer, and ultimately iterate, the established SRF capabilities of the European XFEL in Hamburg into the core technology platform used for the LCLS-II SRF cryomodules. Put simply: it would not have been possible to complete the LCLS-II project, within cost and on schedule, without the sustained cooperation of the European XFEL consortium – in particular, colleagues at DESY, CEA Saclay and several other European laboratories as well as KEK – that generously shared their experiences and know-how. 

Better together 

These days, large-scale accelerator or detector projects are very much a collective endeavour. Not only is the sprawling scope of such projects beyond a single organisation, but the risks of overspend and slippage can greatly increase with a “do-it-on-your-own” strategy. When the LCLS-II project opted for an SRF technology pathway in 2014 to maximise laser performance, the logical next step was to build a broad-based coalition with other US Department of Energy (DOE) national laboratories and universities. In this case, SLAC, Fermilab, Jefferson Lab (JLab) and Cornell University contributed expertise for cryomodule production, while Argonne National Laboratory and Lawrence Berkeley National Laboratory managed delivery of the undulators and photoinjector for the project. For sure, the start-up time for LCLS-II would have increased significantly without this joint effort, extending the overall project by several years.

Each partner brought something unique to the LCLS-II collaboration. While SLAC was still a relative newcomer to SRF technologies, the lab had a management team that was familiar with building large-scale accelerators (following successful delivery of the LCLS). The priority for SLAC was therefore to scale up its small nucleus of SRF experts by recruiting experienced SRF technologists and engineers to the staff team. In contrast, the JLab team brought an established track-record in the production of SRF cryomodules, having built its own machine, the Continuous Electron Beam Accelerator Facility (CEBAF), as well as cryomodules for the Spallation Neutron Source (SNS) linac at Oak Ridge National Laboratory in Tennessee. Cornell, too, came with a rich history in SRF R&D – capabilities that, in turn, helped to solidify the SRF cavity preparation process for LCLS-II. 

Finally, Fermilab had, at the time, recently built two cutting-edge cryomodules of the same style as that chosen for LCLS-II. To fabricate these modules, Fermilab worked closely with the team at DESY to set up the same type of production infrastructure used on the European XFEL. From that perspective, the required tooling and fixtures were all ready to go for the LCLS-II project. While Fermilab was the “designer of record” for the SRF cryomodule, with primary responsibility for delivering a working design to meet LCLS-II requirements, the realisation of an optimised technology platform was a team effort involving SRF experts from across the collaboration.

Collective problems, collective solutions 

While the European XFEL provided the template for the LCLS-II SRF cryomodule design, several key elements of the LCLS-II approach subsequently evolved to align with the continuous-wavelength (CW) operation requirements and the specifics of the SLAC tunnel. Success in tackling these technical challenges – across design, assembly, testing and transportation of the cryomodules – is testament to the strength of the LCLS-II collaboration and the collective efforts of the participating teams in the US and Europe.

Challenges are inevitable when developing new facilities at the limits of known technology

For one, the thermal performance specification of the SRF cavities exceeded the state-of-the-art and required development and industrialisation of the concept of nitrogen doping (a process in which SRF cavities are heat-treated in a nitrogen atmosphere to increase their cryogenic efficiency and, in turn, lower the overall operating costs of the linac). The nitrogen-doping technique was invented at Fermilab in 2012 but, prior to LCLS-II construction, had been used only in an R&D setting.

The priority was clear: to transfer the nitrogen-doping capability to LCLS-II’s industry partners, so that the cavity manufacturers could perform the necessary materials-processing before final helium-vessel jacketing. During this knowledge transfer, it was found that nitrogen-doped cavities are particularly sensitive to the base niobium sheet material – something the collaboration only realised once the cavity vendors were into full production. This resulted in a number of process changes for the heat treatment temperature, depending on which material supplier was used and the specific properties of the niobium sheet deployed in different production runs. JLab, for its part, held the contract for the cavities and pulled out all stops to ensure success.

At the same time, the conversion from pulsed to CW operation necessitated a faster cooldown cycle for the SRF cavities, requiring several changes to the internal piping, a larger exhaust chimney on the helium vessel, as well as the addition of two new cryogenic valves per cryomodule. Also significant is the 0.5% slope in the longitudinal floor of the existing SLAC tunnel, which dictated careful attention to liquid-helium management in the cryomodules (with a separate two-phase line and liquid-level probes at both ends of every module). 

However, the biggest setback during LCLS-II construction involved the loss of beamline vacuum during cryomodule transport. Specifically, two cryomodules had their beamlines vented and required complete disassembly and rebuilding – resulting in a five-month moratorium on shipping of completed cryomodules in the second half of 2019. It turns out that a small (what was thought to be inconsequential) change in a coupler flange resulted in the cold coupler assembly being susceptible to resonances excited by transport. The result was a bellows tear that vented the beamline. Unfortunately, initial “road-tests” with a similar, though not exactly identical, prototype cryomodule had not revealed this behaviour. 

Such challenges are inevitable when developing new facilities at the limits of known technology. In the end, the problem was successfully addressed using the diverse talents of the collaboration to brainstorm solutions, with the available access ports allowing an elastomer wedge to be inserted to secure the vulnerable section. A key take-away here is the need for future projects to perform thorough transport analysis, verify the transport loads using mock-ups or dummy devices, and install adequate instrumentation to ensure granular data analysis before long-distance transport of mission-critical components. 

Upon completion of the assembly phase, all LCLS-II cryo­modules were subsequently tested at either Fermilab or JLab, with one module tested at both locations to ensure reproducibility and consistency of results. For high Q₀ performance in nitrogen-doped cavities, cooldown flow rates of at least 30 g/s of liquid helium were found to give the best results, helping to expel magnetic flux that could otherwise be trapped in the cavity. Overall, cryomodule performance on the test stands exceeded specifications, with a total accelerating voltage per cryomodule of 158 MV (versus specification of 128 MV) and average Q₀ of 3 × 10¹⁰ (versus specification of 2.7 × 10¹⁰). Looking ahead, attention is already shifting to the real-world cryomodule performance in the SLAC tunnel – something that was measured for the first time in 2022.

Transferable lessons

For all members of the collaboration working on the LCLS-II cryomodules, this challenging project holds many lessons. Most important is to build a strong team and use that strength to address problems in real-time as they arise. The mantra “we are all in this together” should be front-and-centre for any multi-institutional scientific endeavour – as it was in this case. Solutions need to be thought of in a more global sense, as the best answer might mean another collaborator taking more onto their plate. Collaboration implies true partnership and a working model very different to a transactional customer–vendor relationship.

From a planning perspective, it’s vital to ensure that the initial project cost and schedule are consistent with the technical challenges and preparedness of the infrastructure. Prototypes and pre-series production runs reduce risk and cost in the long term and should be part of the plan, but there must be sufficient time for data analysis and changes to be made after a prototype run in order for it to be useful. Time spent on detailed technical reviews is also time well spent. New designs of complex components need a comprehensive oversight and review, and should be controlled by a team, rather than a single individual, so that sign-off on any detailed design changes are made by an informed collective. 

LCLS-II science: capturing atoms and molecules in motion like never before

The strobe-like pulses of the LCLS, which produced its first light in April 2009, are just a few millionths of a billionth of a second long, and a billion times brighter than previous X-ray sources. This enables users from a wide range of fields to take crisp pictures of atomic motions, watch chemical reactions unfold, probe the properties of materials and explore fundamental processes in living things. LCLS-II will provide a major jump in capability – moving from 120 pulses per second to 1 million, enabling experiments that were previously impossible. The scientific community has identified six areas where the unique capabilities of LCLS-II will be essential for further scientific progress:

Nanoscale materials dynamics, heterogeneity and fluctuations 

Programmable trains of soft X-ray pulses at high rep rate will characterise spontaneous fluctuations and heterogeneities at the nanoscale across many decades, while coherent hard X-ray scattering will provide unprecedented spatial resolution of material structure, its evolution and relationship to functionality under operating conditions.

Fundamental energy and charge dynamics

High-repetition-rate soft X-rays will enable new techniques that will directly map charge distributions and reaction dynamics at the scale of molecules, while new nonlinear X-ray spectroscopies offer the potential to map quantum coherences in an element-specific way for the first time.

Catalysis and photocatalysis

Time-resolved, high-sensitivity, element- specific spectroscopy will provide the first direct view of charge dynamics and chemical processes at interfaces, characterise subtle conformational changes associated with charge accumulation, and capture rare chemical events in operating catalytic systems across multiple time and length scales – all of which are essential for designing new, more efficient systems for chemical transformation and solar-energy conversion.

Emergent phenomena in quantum materials

Fully coherent X-rays will enable new high- resolution spectroscopy techniques to map the collective excitations that define these new materials in unprecedented detail. Ultrashort X-ray pulses and optical fields will facilitate new methods for manipulating charge, spin and phonon modes to both advance fundamental understanding and point the way to new approaches for materials control.

Revealing biological function in real time

The high repetition rate of LCLS-II will provide a unique capability to follow the dynamics of macromolecules and interacting complexes in real time and in native environments. Advanced solution-scattering and coherent imaging techniques will characterise the conformational dynamics of heterogeneous ensembles of macromolecules, while the ability to generate “two-colour” hard X-ray pulses will resolve atomic-scale structural dynamics of biochemical processes that are often the first step leading to larger-scale protein motions.

Matter in extreme environments

The capability of LCLS-II to generate soft and hard X-ray pulses simultaneously will enable the creation and observation of extreme conditions that are far beyond our present reach, with the latter allowing the characterisation of unknown structural phases. Unprecedented spatial and temporal resolution will enable direct comparison with theoretical models relevant for inertial-confinement fusion and planetary science.

Work planning and control is another essential element for success and safety. This idea needs to be built into the “manufacturing system”, including into the cost and schedule, and to be part of each individual’s daily checklist. No one disagrees with this concept, but good intentions on their own will not suffice. As such, required safety documentation should be clear and unambiguous, and be reviewed by people with relevant expertise. Production data and documentation need to be collected, made easily available to the entire project team, and analysed regularly for trends, both positive and negative. 

Supply chain, of course, is critical in any production environment – and LCLS-II is no exception. When possible, it is best to have parts procured, inspected, accepted and on-the-shelf before production begins, thereby eliminating possible workflow delays. Pre-stocking also allows adequate time to recycle and replace parts that do not meet project specifications. Also worth noting is that it’s often the smaller components – such as bellows, feedthroughs and copper-plated elements – that drive workflow slowdowns. A key insight from LCLS-II is to place purchase orders early, stay on top of vendor deliveries, and perform parts inspections as soon as possible post-delivery. Projects also benefit from having clearly articulated pass/fail criteria and established procedures for handling non-conformance – all of which alleviates the need to make critical go/no-go acceptance decisions in the face of schedule pressures.

As with many accelerator projects, LCLS-II is not an end-point in itself, more an evolutionary transition within a longer term roadmap

Finally, it’s worth highlighting the broader impact – both personal and professional – on individual team members participating in a big-science collaboration like LCLS-II. At the end of the build, what remained after designs were completed, problems solved, production rates met, and cryomodules delivered and installed, were the friendships that had been nurtured over several years. The collaboration amongst partners, both formal and informal, who truly cared about the project’s success, and had each other’s backs when there were issues arising: these are the things that solidified the mutual respect, the camaraderie and, in the end, made LCLS-II such a rewarding project.

First light

In April 2022 the new LCLS-II linac was successfully cooled to its 2 K operating temperature. The next step was to pump the SRF cavities with more than a megawatt of microwave power to accelerate the electron beam from the new source. Following further commissioning of the machine, first X-rays are expected to be produced in early 2023. 

As with many accelerator projects, LCLS-II is not an end-point in itself, more an evolutionary transition within a longer term roadmap. In fact, work is already under way on LCLS-II HE – a project that will increase the energy of the CW SRF linac from 4 to 8 GeV, enabling the photon energy range to be extended to at least 13 keV, and potentially up to 20 keV at 1 MHz repetition rates. To ensure continuity of production for LCLS-II HE, 25 next-generation cryomodules are in the works, with even higher performance specifications versus their LCLS-II counterparts, while upgrades to the source and beam transport are also being finalised. 

While the fascinating science opportunities for LCLS-II-HE continue to be refined and expanded, of one thing we can be certain: strong collaboration and the collective efforts of the participating teams are crucial. 

• This is an updated version of an article published in 2021 in a CERN Courier “In Focus” issue about US accelerator projects.

The post First light beckons at SLAC’s LCLS-II appeared first on CERN Courier.

The Synchrotron-light for Experimental Science and Applications in the Middle East (SESAME) is a 2.5 GeV third-generation synchrotron radiation (SR) source developed under the auspices of UNESCO and modelled after CERN. Located in Allan, Jordan, it aims to foster scientific and technological excellence as well as international cooperation amongst its members, which are currently Cyprus, Egypt, Iran, Israel, Jordan, Pakistan, Palestine and Turkey. As a user facility, SESAME hosts visiting scientists from a wide range of disciplines, allowing them to access advanced SR techniques that link the functions and properties of samples and materials to their micro, nano and atomic structure.

The location of SESAME is known for its richness in archaeological and cultural heritage. Many important museums, collections, research institutions and universities host departments dedicated to the study of materials and tools that are inextricably linked to prehistory and human history, demanding interdisciplinary research agendas and teams. As materials science and condensed-matter physics play an increasing role in understanding and reconstructing the properties of artefacts, SESAME offers a highly versatile tool for the researchers, conservators and cultural-heritage specialists in the region.

The high photon flux, small source size and low divergence available at SR sources allow for advanced spectroscopy and imaging techniques that are well suited for studying ancient and historical materials, and which often present very complex and heterogeneous structures. SR techniques are non-destructive, and the existence of several beamlines at SR facilities means that samples can easily be transferred and reanalysed using complementary techniques.

SESAME offers a versatile tool for researchers, conservators and cultural-heritage specialists in the region

At SESAME, an infrared microspectroscopy beamline, an X-ray fluorescence and absorption spectroscopy beamline, and a powder diffraction beamline are available, while a soft X-ray beamline called “HESEB” has been designed and constructed by five Helmholtz research centres and is now being commissioned. Next year, the BEAmline for Tomography at SESAME (BEATS) will also be completed, with the construction and commissioning of a beamline for hard X-ray full-field tomography. BEATS involves the INFN, The Cyprus Institute and the European SR facilities ALBA-CELLS (Spain), DESY (Germany), ESRF (France), Elettra (Italy), PSI (Switzerland) and SOLARIS (Poland).

To explore the potential of these beamlines, the First SESAME Cultural Heritage Day took place online on 16 February with more than 240 registrants in 39 countries. After a welcome by SESAME director Khaled Toukan and president of council Rolf Heuer, Mohamed ElMorsi (Conservation Centre, National Museum of Egyptian Civilization), Marine Cotte (ESRF) and Andrea Lausi (SESAME) presented overviews of ancient Egyptian cultural heritage, heritage studies at the ESRF, and the experimental capabilities of SESAME, respectively. This was followed by several research insights obtained by studies at SESAME and other SR facilities: Maram Na’es (TU Berlin) showed the reconstruction of colour in Petra paintings; Heinz-Eberhard Mahnke and Verena Lepper (Egyptian Museum and Papyrus Collection, FU/HU Berlin and HZB) explained how to analyse ancient Elephantine papyri using X-rays and tomography; Amir Rozatian (University of Isfahan) and Fatma Marii (University of Jordan) determined the material of pottery, glass, metal and textiles from Iran and ancient glass from the Petra church; and Gonca Dardeniz Arıkan (Istanbul University) provided an overview of current research into the metallurgy of Iran and Anatolia, the origins of glassmaking, and the future of cultural heritage studies in Turkey. Palaeontology with computed tomography and bioarchaeological samples were highlighted in talks by Kudakwashe Jakata (ESRF) and Kirsi Lorentz (The Cyprus Institute).

During the following discussions, it was clear that institutions devoted to the research, preservation and restoration of materials would benefit from developing research programmes in close cooperation with SESAME. Because of the multiple applications in archaeology, palaeontology, palaeo-environmental science and cultural heritage, it will be necessary to establish a multi-disciplinary working group, which should also share its expertise on practical issues such as handling, packaging, customs paperwork, shipping and insurance. 

The post SESAME revives the ancient Near East appeared first on CERN Courier.

Tens of thousands of accelerators around the world help create radiopharmaceuticals, treat cancer, preserve food, monitor the environment, strengthen materials, understand fundamental physics, study the past, and even disclose crimes.

A first of its kind international conference, Accelerators for Research and Sustainable Development: From Good Practices Towards Socioeconomic Impact was organised by the International Atomic Energy Agency (IAEA) at its headquarters in Vienna from 23 to 27 May. It was held as a hybrid event attended by around 500 scientists from 72 IAEA member states. While focusing mainly on applications of accelerator science and technology, the conference was geared towards accelerator technologists, operators, users, entrepreneurs, and other stakeholders involved in applications of accelerator technologies as well as policy makers and regulators.

The far-reaching capabilities of accelerator technology help countries progress towards sustainable development

Rafael Mariano Grossi

“The far-reaching capabilities of accelerator technology help countries progress towards sustainable development,” said IAEA director general Rafael Mariano Grossi in his opening address. “IAEA’s work with accelerators helps to fulfil a core part of its ‘Atoms for Peace and Development’ mandate.” He also highlighted how accelerator technology plays a critical role in two IAEA initiatives launched over the past year: Rays of Hope, aimed at improving access to radiotherapy and cancer care in low- and middle-income countries, and NUTEC plastics, supporting countries in addressing plastic waste issues in the ocean and on land. Finally, he described IAEA plans to establish an accelerator of its own: a state-of-the-art ion-beam facility in Seibersdorf, Austria that will support research and help educate and train scientists.

The conference included sessions dedicated to case studies demonstrating socioeconomic impact as well as best practices in effective management, safe operation, and the sustainability of present and future accelerator facilities. It showcased the rich diversity in types of accelerators – from large-scale synchrotrons and spallation neutron sources, or medical cyclotrons and e-beam irradiators used for industrial applications, to smallscale electrostatic accelerators and compact-accelerator based neutron sources – and included updates in emerging accelerator technologies, such as laser-driven neutron and X-ray sources and their future applications. Six plenary sessions featuring 16 keynote talks captured the state of the art in various application domains, accompanied by 16 parallel and two poster sessions by young researchers.

During the summary and highlights session, important developments and future trends were presented:

Accelerator technologies evolve very fast, presenting a challenge for regulatory bodies to authorise and inspect accelerator facilities and activities. This conference demonstrated that thanks to recent technological breakthroughs in accelerator technology and associated instrumentation, accelerators are becoming an equally attractive alternative to other sources of ionising radiation such as gamma irradiators or research reactors, among other conventional techniques. Based on the success of this conference, it is expected that the IAEA will start a new series of accelerator community gatherings periodically from now on every two to three years.

The post Accelerating a better world appeared first on CERN Courier.

At 4.47 p.m. on Tuesday 5 July, applause broke out in the CERN Control Centre as LHC operators declared Stable Beams. After more than three years of upgrade and maintenance work across the machine and experiments, ALICE, ATLAS, CMS and LHCb started recording their first proton–proton collisions at an unprecedented energy of 13.6 TeV. 

LHC Run 3 is set to last until December 2025. In addition to a slightly higher centre-of-mass energy than Run 2, the machine will operate at an increased average luminosity thanks to larger proton intensities and smaller transverse beam sizes. New or upgraded detectors and improved data readout and selection promise the experiments their greatest physics harvests yet. ATLAS and CMS each expect to record more collisions during Run 3 than in the two previous runs combined, while LHCb and ALICE hope for three and 50 times more data, respectively. Two new forward experiments, FASER and SND@LHC (CERN Courier July/August 2021 p7), also join the LHC-experiment family. 

While pilot beams circulated in the LHC for a brief period in October 2021, the countdown to LHC Run 3 began in earnest on 22 April, when two beams of protons circulated in opposite directions at their injection energy of 450 GeV. Since then, operators have worked around the clock to ensure the smooth beginning of the LHC’s third run, which was livestreamed to the media on the afternoon of 5 July. True to form, the machine added drama to proceedings: a training quench that morning generated enough heat to warm up several magnets well above their operating temperature. The cryogenics team sprang into action, managing to recuperate operational conditions just in time for the live event, watched by more than 1.5 million people. 

Since then, the intensity of the beams has been increased in carefully monitored steps. As the Courier went to press, 900 bunches each containing around 120 billion protons were circulating, with 2748 bunches expected by September. “Run 3 is going to be a game-changer for us,” says operations group leader Rende Steerenberg. “In Run 2, we exploited the LHC in its ‘normal’ hardware configuration as constructed. Now, after the injectors have been adapted, we can push the brightness and the intensity of the beams much more. Run 3 is also an important stepping-stone to the High-Luminosity LHC upgrade.” 

Schedule change

In March, the CERN management announced a change to the LHC schedule. Long Shutdown 3 will now start in December 2025, one year later than in the previous baseline, and last for three instead of 2.5 years. Production schedules across the LHC’s lifetime will remain unaffected, while the change will allow work for the HL-LHC to be completed with appropriate schedule margins. The extended year-end technical stop (EYETS) is now scheduled to take place in 2024/2025 and to last for 17 weeks, while the two preceding EYETSs will be of the standard length of 13 weeks beam-to-beam. 

The preferred scenarios and duration of ion runs during Run 3 remain to be confirmed, but are likely to take place in four week-long periods towards the end of each year. While the majority of the LHC’s heavy-ion runs employ lead ions, a novel addition to the Run 3 programme will be a short period of collisions between oxygen ions in 2024. As with the first xenon runs in 2017, colliding ions with masses that are intermediate between protons and lead allows the experiments to scan important physics regimes relevant to the study of high-energy QCD. 

“Every time you make a step in energy, even if it’s not that large, and a step in the amount of data, you open up new physics opportunities,” said CERN Director-General Fabiola Gianotti. “And every time we start a new run, it’s always a new adventure. You have to recalibrate the detectors and the accelerator, so it’s always uncharted territory and always a big emotion.” 

• For full coverage of the physics targets at LHC Run 3, please see the May/June 2022 issue of CERN Courier.

The post Run 3 physics gets under way appeared first on CERN Courier.

The first Italian workshop on the Future Circular Collider (FCC) took place in Rome from 21 to 22 March and was attended by around 120 researchers.

The FCC study is exploring the technical and financial feasibility of a 91 km-circumference collider situated under French and Swiss territory near CERN, thus exploiting existing infrastructures. In a first phase (FCC-ee) the tunnel would host an electron–positron collider at energies from 90 to 365 GeV, which would be replaced by a proton–proton collider (FCC-hh) with a centre-of-mass energy of at least 100 TeV, almost an order of magnitude higher than that of the LHC. The proposed roadmap foresees the R&D for the 16 T superconducting dipole magnets needed to keep the FCC-hh proton beams on track to take place in parallel with FCC-ee construction and operation. 

“The FCC is a large infrastructure that would allow Europe to maintain its worldwide leadership in high-energy physics research. This project is therefore of strategic importance in the international science scenario of the coming years,” remarked INFN president Antonio Zoccoli in his introduction. “INFN has great potential and could make a significant contribution to its implementation. In this perspective, it is important to clearly identify the main activities in which to invest, assemble the necessary human resources and identify possible industrial partners.”

The workshop was opened by FCC study leader Michael Benedikt, who gave an overview of the FCC feasibility study, while deputy study leader Frank Zimmermann covered the technological challenges, design features and machine studies for FCC-ee. Opportunities for technological development related to the FCC-ee were then presented, along with machine studies, in which INFN are already involved. Scientific and technological R&D areas where collaborations could be strengthened or initiated were also identified, prompting an interesting discussion with CERN colleagues. 

INFN is already well integrated both in the FCC coordination structure and several ongoing studies, having participated in the project since its beginning, and provides important contributions on all aspects of the FCC study. These range from accelerator and detector R&D, such as the development of superconducting magnets, to experimental and theoretical physics studies. This is made evident by the strong Italian involvement in FCC-related European programmes, such as EuroCirCol for FCC-hh and FCC-IS for FCC-ee, and AIDAinnova on innovative detector technologies for future accelerators. INFN is committed to the development of superconducting magnets for FCC-hh, for which substantial additional funding could come from a project in the context of the next-generation funding programme Horizon Europe.

The second day of the workshop focused on the work that experimental and theoretical physicists have been carrying out to deeply understand the scientific potential of the visionary FCC project, the specific requests for the detectors and the associated R&D activities.

This workshop was the first in a series organised by INFN to promote and support the FCC project and pursue the key technological R&D needed to demonstrate its feasibility by the next update of the European strategy for particle physics.

The post Future Circular Collider workshop debuts in Italy appeared first on CERN Courier.

The cryogenic infrastructure of the Large Hadron Collider (LHC) at CERN is the most complex helium refrigeration system of all the world’s research facilities.

The operation of the LHC’s cryogenic system was initiated in 2008 after reception testing and a first cool down to 1.9 K. This webinar will cover information on the design, operational experiences and main challenges linked to the accelerator, along with the physics requirements.

During the first stage, the operation team had to learn about the responsivity and limitations of the system. They then had to manage stable operation by maintaining the necessary conditions for the superconducting magnets, RF cavities, electrical feed boxes, power links and detector devices, thus contributing to the physics programme and the discovery of the Higgs boson in 2012.

One of the most challenging parameters impacting the cryogenics was the beam-induced heat load that was taken up, beginning during the second operation period (Run 2) of the LHC in 2015 with increased beam parameters. A complicated optimisation of the configuration of the cryogenic system was successfully applied to cope with these requirements.

Run 3 (preparation for which started in 2020) required the handling of several hundred magnet training quenches towards the nominal beam energy for physics production.

Now, after several years of operational experience with steady state and transient handling, the cryogenic system is being optimised to provide the necessary refrigeration, whilst incorporating the all-important aspect of energy preservation.

In conclusion, there will be a brief discussion of the next four years of operation.

Krzysztof Brodzinski is a senior staff member in the cryogenics group at the technology department at CERN. He is a mechanical engineer with a specialisation in refrigeration equipment, and graduated from Cracow University of Technology in Poland. Krzysztof  joined the LHC cryogenic design team in 2001, has been a member of the cryogenic operation team since 2009 and in 2019 was mandated as a section leader of the cryogenic operation team for the LHC, ATLAS and CMS. He is also involved in the engineering of the cryogenic system for the HiLumi LHC RF deflecting cavities project, as well as participating in the ongoing FCC cryogenics study.

The post The LHC cryogenics and its adaptation to the operational parameters for beams, related physics and energy preservation appeared first on CERN Courier.

19 September 2008: the LHC was without beam because of a transformer problem. The hardware commissioning team were finishing off powering tests of the main dipole magnet circuit in sector 3–4 when, at 11:18, an electrical fault resulted in considerable physical damage, the release of helium, and debris in a long section of the machine. In the control room, the alarms came swamping in. The cryogenics team grappled to make sense of what their systems were telling them, and there was frantic effort to interpret the data from the LHC’s quench protection system. I called LHC project leader Lyn Evans: “looks like we’ve got a serious problem here”.

Up to this point, 2008 had been non-stop but things were looking good. First circulating beam had been established nine days earlier in a blaze of publicity. Beam commissioning had started in earnest, and the rate of progress was catching some of us by surprise.

It is hard to describe how much of a body blow the sector 3–4 incident was to the community. In the following days, as the extent of the damage became clearer, I remember talking to Glyn Kirby of the magnet team and being aghast when he observed that “it’s going to take at least a year to fix”. He was, of course, right.

What followed was a truly remarkable effort by everyone involved. A total of 53 cryomagnets (39 dipoles and 14 quadrupoles) covering most of the affected 700 m-long zone were removed and brought to the surface for inspection, cleaning and repair or reuse. Most of the removed magnets were replaced by spares. All magnets whatever their origin had to undergo full functional tests before being installed.

Soot in the vacuum pipes, which had been found to extend beyond the zone of removed magnets, was cleared out using endoscopy and mechanical cleaning. The complete length of the beam pipes was inspected for contamination by flakes of multilayer insulation, which were removed by vacuum cleaning. About 100 plug-in modules installed in the magnet interconnects were replaced. 

Following an in-depth analysis of the root causes of the incident, and an understanding of the risks posed by the joints in the magnet interconnects, a new worst-case Maximum Credible Incident was adopted and a wide range of recommendations and mitigation measures were proposed and implemented. These included a major upgrade of the quench protection system, new helium pressure-release ports, and new longitudinal restraints for selected magnets. 

One major consequence of the 19 September incident was the decision to run at a lower-than-design energy until full consolidation of the joints had been performed – hence the adoption of an operational beam energy of 3.5 TeV for Run 1. Away from the immediate recovery, other accelerator teams took the opportunity to consolidate and improve controls, hardware systems, instrumentation, software and operational procedures. As CMS technical coordinator Austin Ball famously noted, come the 2009 restart, CMS, at least, was in an “unprecedented state of readiness”. 

Take two

Beam was circulated again on 20 November 2009. Progress thereafter was rapid. Collisions with stable-beam conditions were quickly established at 450 + 450 GeV, and a ramp to the maximum beam energy at the time (1.18 TeV, compared to the Tevatron’s 0.98 TeV) was successfully performed on 30 November. The first ramps were a lot of fun – there’s a lot going on behind the scenes, including compensation of significant field dynamics in the superconducting dipoles. Cue much relief when beam made it up the ramp for the first time. All beam-based systems were at least partially commissioned and LHC operations started a long process to master the control of a hugely complex machine. Following continued deployment of the upgraded quench protection system during the 2009 year-end technical stop, commissioning with beam started again in the new year. Progress was good, with first colliding beams at 3.5 + 3.5 TeV being established under the watchful eye of the media on 30 March 2010. With scheduled collisions delayed by two unsuccessful ramps, it was a gut-knotting experience in the control room. Nonetheless, we finally got there about three hours late. “Stable Beams” was declared, the odd beer was had, and we were off. 

Essentially 2010 was then devoted to commissioning and establishing confidence in operational procedures and the machine protection system, before starting to increase the number of bunches in the beam. In June the decision was taken to go for bunches with nominal population (~1.2 × 10¹¹ protons), which involved another extended commissioning period. Up to this point, in deference to machine-protection concerns, only around one fifth of the nominal bunch population had been used. To further increase the number of bunches, the move to a bunch separation of 150 ns was made and the crossing angle bumps spanning the experiments’ insertion regions were deployed. After a carefully phased increase in total intensity, the proton run finished with beams of 368 bunches of around 1.2 × 10¹¹ protons per bunch, and a peak luminosity of 2.1 × 10³² cm^–2s^–1.

Looking back, 2010 was a profoundly important year for a chastened and cautious accelerator sector. The energy stored in the magnets had demonstrated its destructive power, and it was clear from the start that the beam was to be treated with the utmost respect; safe exploitation of the machine was necessarily an underlying principle for all that followed. The LHC became magnetically and optically well understood (judged by the standards at the time – impressively surpassed in later years), and was stunningly magnetically reproducible. The performance of the collimation system was revelatory and accomplished its dual role of cleaning and protection impeccably throughout the full cycle. The injectors were doing a great job throughout in reliably providing high-intensity bunches with unforeseen low transverse emittances.

2010 finished with a switch from protons to operations with lead ions for the first time. Diligent preparation and the experience gained with protons allowed a rapid execution of the ion commissioning programme and Stable Beams for physics was declared on 7 November. 

Homing in 

The beam energy remained at 3.5 TeV in 2011, with the bunch spacing switched from 75 to 50 ns. A staged ramp in the number of bunches then took place up to a maximum of 1380 bunches, and performance was further increased by reducing the transverse size of the beams delivered by the injectors and by gently increasing the bunch population. The result was a peak luminosity of 2.4 × 10³³ cm^–2s^–1 and some healthy delivery rates that topped 90 pb^–1 in 24 hours. The next step-up in peak luminosity followed a reduction in the β^* parameter in ATLAS and CMS from 1.5 to 1 m (the transverse beam size at the interaction point is directly related to the value of β*). Along with further gentle increases in bunch population, this produced a peak luminosity of 3.8 × 10³³ cm^–2s^–1 – well beyond expectations at the start of the year. Coupled with a concerted effort to improve availability, the machine went on to deliver a total of around 5.6 fb^–1 for the year to both ATLAS and CMS. 

Meanwhile, excitement was building in the experiments. A colloquium at the end of 2011 showed a strengthening significance of an excess at around 125 GeV. The possible discovery of the Higgs boson in 2012 was recognised, and corresponding LHC running scenarios were discussed in depth – first at the Evian workshop (where we heard the plea from CMS spokesperson Guido Tonelli to “gimme 20” [inverse femtobarns]) and crystallised at the 2012 Chamonix workshop, where CERN Director-General Rolf Heuer stated: as a top priority the LHC machine must produce enough integrated luminosity to allow the ATLAS and CMS experiments an independent discovery of the Higgs before the start of long shutdown 1 (LS1). Soon after the workshop, Council president Michel Spiro sent a message to CERN’s member states: “After a brilliant year in 2011, 2012 should be historic, with either the discovery of the Standard Model Higgs boson or its exclusion.”

An important decision concerned the energy. A detailed risk evaluation concluded that the probability of a splice burn-out at 4 TeV per beam in 2012 was equal to, or less than, the probability that had been estimated in 2011 for 3.5 TeV per beam. The decision to run at 4 TeV helped in a number of ways: higher cross-sections for Higgs-boson production, reduced emittance and the possibility for a further reduction of β^*.

Discovery year 

And so 2012 was to be a production year at an increased beam energy of 4 TeV. The choice was made to continue to exploit 50 ns bunch spacing, which offered the advantages of less electron cloud and higher bunch charge compared with 25 ns, and to run with 1380 bunches. Based on the experience of 2011, it was also decided to operate with tight collimator settings, enabling a more aggressive squeeze to β^* = 0.6 m. The injectors continued to provide exceptional quality beam and routinely delivered 1.7 × 10¹¹ protons per bunch. The peak luminosity quickly rose to its maximum for the year, followed by determined and long running attempts to improve peak performance. Beam instabilities, although never debilitating, were a reoccurring problem and there were phases when they cut into operational efficiency. Nonetheless by the middle of the year another 6 fb^–1 had been delivered to both ATLAS and CMS. Combined with the 2011 dataset, this paved the way for the announcement of the Higgs-boson discovery. 

After a brilliant year in 2011, 2012 should be historic, with either the discovery of the Standard Model Higgs boson or its exclusion

2012 was a very long operational year and included the extension of the proton–proton run until December to allow the experiments to maximise their 4 TeV data before LS1. Integrated-luminosity rates were healthy at around 1 fb^–1 per week, and the total for the year came in at about 23 fb^–1 to both ATLAS and CMS. Run 1 finished with four weeks of proton–lead operations at the start of 2013.

It is impossible to do justice to the commitment and effort that went into establishing, and then maintaining, the complex operational performance of the LHC that underpinned the Higgs-boson discovery: RF, power converters, collimation, injection and beam-dump systems, vacuum, transverse feedback, machine protection, cryogenics, magnets, quench detection and protection, accelerator physics, beam instrumentation, beam-based feedbacks, controls, databases, software, survey, technical infrastructure, handling engineering, access, radiation protection plus material science, mechanical engineering, laboratory facilities … and the coordination of all that! 

The post The bumpy ride to the bump appeared first on CERN Courier.

This webinar is focused on the technology of the superconducting magnets used in the LHC. After reviewing the equations for an electromagnet, we show how superconductivity enables much larger magnetic fields in very compact devices, thanks to the possibility of increasing the current density in the windings by more than two order of magnitudes with respect to resistive conductors. We then outline the development of superconducting accelerator magnets from the ISR quadrupoles, up to the LHC and beyond.

We conclude by describing the successive increases of LHC energy since 2008 up to the 6.8 TeV per beam recently achieved, and show how the control of field imperfections has been an essential element for reaching the ultimate luminosity.

Ezio Todesco was born in Bologna Italy, where he got a PhD in physics. In the 90’s, after a master thesis at CERN, he worked at the Italian national institute of nuclear physics (INFN) on topics related to nonlinear dynamics of particle accelerators, and long-term stability in the planned Large Hadron Collider. He joined the magnet group at CERN in 1998, and has been in charge of the field quality follow-up of the LHC main dipoles and quadrupole during the five-year-long magnet production. After the completion of the production phase, he has been in charge of the magnetic field model of the LHC, following the initial commissioning and the successive energy increases up to 13 TeV centre of mass. Then, he has been involved in the studies of the LHC luminosity upgrade, and he leads the interaction region magnets for HL-LHC since the beginning of the project in 2015.

The post Superconducting magnets: an enabling technology for the discovery of the Higgs boson appeared first on CERN Courier.

This webinar, presented by Frank Gerigk, will provide an overview of the LHC RF system, its superconducting cavities and RF power system. It also introduce the changes, which will be implemented to accelerate the high-intensity beams of the HL-LHC era.

Join this webinar to:
• Learn about the technology that accelerates LHC protons from 450 GeV to 7 TeV.
• Appreciate the development of the superconducting cavities used in the LHC.
• Understand how the LHC system will be modified for HL-LHC and how crab cavities will increase the number of collisions.

Frank Gerigk is the leader of the Radio Frequency (RF) Group at CERN. After graduating at the Technical University Berlin in 1999, he came to CERN as a fellow to work on RF and beam dynamics for linear accelerators. In 2002, he became staff member at the Rutherford Appleton Laboratory in the UK, continuing with beam dynamics and focussing on halo development in hadron beams. After his return to CERN in 2005, Frank joined the RF group and soon became responsible for the Linac4 RF cavities. He became section leader for Linac RF in 2012, and then for Superconducting RF in 2018. Since 2020 he has been leading the RF group in the new Systems Department.

The post RF technology for LHC and HL-LHC appeared first on CERN Courier.

An advisory panel to the Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) has called on proponents of the International Linear Collider (ILC) to re-evaluate their plans. In particular, noting the global situation and the progress in other future-collider proposals, the expert panel recommends that the issue of Japan hosting the ILC should be temporarily shelved in forthcoming ILC activities.

The Japanese high-energy physics community proposed Japan to host the ILC shortly after the discovery of the Higgs boson in 2012. Since then, MEXT and bodies including the Science Council of Japan (SCJ) have been examining all aspects of the estimated $7 billion project, which would collide electrons and positrons to study the Higgs boson in detail. In 2018 the International Committee for Future Accelerators (ICFA) backed a 20 km-long ILC operating at a centre-of-mass energy of 250 GeV – half the energy set out in the 2013 technical design report. But the following year MEXT, with input from the SCJ, announced that it had “not yet reached declaration” for hosting the ILC and that further discussion and greater international commitment were necessary.

Planning and progress

In June 2021, a 50 page-long report published by the ILC International Development Team (IDT), which was established in 2020, set out the organisational framework, implementation model, work plan and required resources for an ILC “pre-lab”. At the same time, KEK and the Japan Association of High Energy Physicists submitted a report to MEXT summarising progress on ILC activities over the past three years. Having evaluated this progress, the ILC advisory panel to MEXT released its findings on 14 February.

While recognising the academic significance of particle physics, the importance of a Higgs factory and the value of international collaborative research, the panel concluded that there is no progress in the international cost sharing for the ILC and that it is premature to proceed with an ILC pre-lab based on the premise that the Japanese government will express its interest in hosting the facility. It recommended that ILC proponents reflect upon the increasing strain in the financial situation of the related countries and reevaluate the plan in a global manner, in particular taking into account the progress in studies such as the Future Circular Collider (FCC). The question of hosting the ILC in Japan should be “decoupled”, recommended the report, and development work in key technological areas be carried out by further strengthening the international collaboration among institutes and laboratories. The panel also urged the research community to continue efforts to expand the broad support from various stakeholders in Japan and abroad by building up trust and mutual understanding.

Responding to the advisory panel’s findings on 22 March, KEK stated that it will re-examine the path for realising the ILC as a Higgs factory, taking into account the progress in various fronts including the FCC feasibility study. Also, in collaboration with the ILC-IDT, KEK will propose a framework to ICFA to address some of the pressing accelerator R&D issues for the ILC pre-lab. “KEK and the Japanese ILC community is committed to further advance important technological and engineering development in the accelerator area,” stated KEK, also announcing a new centrally managed organisation to strengthen ILC communications to the public, academia and industry.

Writing in ILC Newsline on 22 March, ILC-Japan chair Shoji Asai of the University of Tokyo sought to clarify the advisory panel’s statements, pointing out the “rather ambiguous” Japanese language: “It is easy to react by saying ‘ILC is dead’ or ‘Japan is not interested’. However, this is not a project that can be talked about in such a simple manner.” Regarding the panel’s statement about the FCC: “Some interpret this line as the recommendation to choose between the ILC and the FCC. It is NOT. There is a clear understanding of the timing difference between the two projects.”

On 11 April, ICFA published a statement reaffirming its position that the concept for the ILC is technically robust and has reached a level of maturity “which supports its moving forward with the engineering design study toward its timely realisation”. ICFA commits to continuing efforts within the IDT over the next year to coordinate the global research community’s activities, in particular to further strengthen international collaboration among institutes and laboratories to advance international collaboration toward important R&D activities, and will continue to encourage intergovernmental discussion between Japan and potential partner nations on the ILC.

“Since Japan has never hosted a large international research facility in the past, the cautious attitude of the Japanese government is in some way understandable,” says Tatsuya Nakada, head of the ILC-IDT. “Linear colliders should remain as a viable option for the future Higgs factory and beyond. In this context, ICFA support for the Japanese community proposing the ILC as a global project hosted in Japan is very important.”

The post Reports evaluate case for the ILC in Japan appeared first on CERN Courier.

In preparing the long-term future of high-energy physics after the LHC, the 2020 update of the European strategy for particle physics recommended that Europe, together with its international partners, explore the technical and financial feasibility of a future proton–proton collider at CERN with a centre-of-mass energy of at least 100 TeV, and with an electron–positron Higgs and electroweak factory as a possible first stage. In 2021 a new chapter opened for the Future Circular Collider (FCC) feasibility study with the development of the preferred layout and placement scenario for this visionary possible new research infrastructure.

Following the publication of the FCC conceptual design report in 2019, an interdisciplinary team from CERN and CERN’s host-state authorities worked to ensure that the preferred placement scenario aligned with the regional requirements and environmental constraints in France and Switzerland. This included Cerema (the Centre for Studies and Expertise on Risks, the Environment, Mobility and Urban Planning) in France and departments from the Canton of Geneva. A key challenge in constructing a new 90–100 km-circumference tunnel for a future collider concerns subsurface areas. Here, the FCC study has brought together international leaders in the construction industry along with French and Swiss universities, thus profiting from local expertise, to develop geological studies. Thanks to this colossal effort, more than 100 scenarios with different layout geometries and surface sites have been analysed, leading to a number of potential options. 

Preferred placement

In June 2021 an international committee independently reviewed the results of these studies, recommending a specific, 91 km-circumference layout with a four-fold symmetry and eight surface sites (see “Closing the loop” image). This configuration balances the requirement for maximising the scientific output of the FCC within territorial constraints and project implementation risks. To validate the feasibility of this placement scenario, further data about the surface and the geology are needed. This entails specific site investigations to optimise the locations of surface sites in view of infrastructure and environmental constraints, and to gain a more realistic understanding of the geological conditions. 

In line with these planned activities, the Préfet de la Région Auvergne-Rhône-Alpes has been mandated by the French government to coordinate the involvement of all relevant services in France in close cooperation with Switzerland, and the local authorities and communities potentially affected by such a project. A few weeks later, on 10 December, the Swiss Federal Council announced its decision to strengthen support for current CERN projects and future developments, including the FCC: “In addition to its considerable contributions to science and innovation, CERN has also brought significant economic benefits to Switzerland, and the Geneva region in particular,” stated the Federal Council announcement. “Switzerland must promote CERN’s long-term development potential, particularly in terms of spatial planning, which has prompted the Federal Council to initiate work on a federal sectorial plan focusing on CERN projects.” 

In parallel with activities at the federal level, the Canton of Geneva has created a support unit involving about 20 different offices to work with CERN. The first meeting between the newly established group and the CERN FCC team took place in December 2021, paving the way for a roadmap of activities from 2022 onwards to analyse the FCC requirements and the constraints that will apply during the different project phases.

Local engagement

As the FCC feasibility study moves from a generic to a specific geographical level, dialogues between government officials, local elected representatives and citizens become increasingly important. Consequently, CERN – together with France and Switzerland – has created a permanent group to communicate with all stakeholders in both countries. The first activities involve identifying and analysing the needs and expectations of the populations in the relevant areas, and preparing non-invasive activities on the surface, such as environmental analyses and detailed planning of geophysical and geotechnical investigations to be carried out from 2024.

Developing a scenario for such a geographically distributed infrastructure raises numerous challenges at both large and small scales, and therefore calls for thoughtful planning. One example is the connection of surface sites to the French high-capacity electrical network, which involves planning for electricity lines with voltages above 63 kV. A second example is the connection between selected surface sites and the transport network to allow the efficient removal of excavated materials and the movement of construction materials. At the local level, one of the issues that working groups in France and Switzerland face is the provision of land plots. Since the launch of the FCC study in 2014, no less than 400 ha of candidate surface-site areas had to be discarded due to the designation of new environmental protection zones, agricultural protection areas and the development of housing and infrastructure projects. 

Despite the long time scales involved, the local population should already be engaged from the feasibility study stage in developing the vision for CERN’s post-LHC future. This year, a series of meetings will take place with the communes that would potentially host the surface sites in both France and Switzerland. The activity will be accompanied by an environmental initial-state analysis and an agricultural-economics study, which will create the baselines for impact studies. These, in turn, will form the cornerstone of the Éviter-réduire-compenser (avoid-reduce-compensate) principle, anchored in French environmental law, which the FCC study has adopted from the beginning to ensure a well-balanced, scientifically excellent and territorially acceptable project scenario. A further issue that should be carefully explored is the accessibility of the surface sites; certain candidate areas are in zones that lack road or train access, for example. It is also important for regional administration services in France and Switzerland to establish contacts for FCC-related trans-border traffic in time to understand the needs and the possibilities on a time frame of 10–15 years.

Building the future

These recent developments offer a glimpse of the ongoing work needed to prepare for a new research infrastructure in the Geneva region, and highlight the importance of the timely completion of a geo-localised scenario on a timescale of around a decade. In parallel, machine, detector and physics studies by the global FCC collaboration continue across 150 institutes in 30 countries. 

Despite the long time scales involved, the local population should already be engaged from the feasibility study stage

It takes time and care to build a mutual understanding of the possibilities and constraints, both within the engineering domains at CERN and the public administration services in France and Switzerland, along with the development of the required legal and administrative frameworks. Tripartite working-group meetings involving CERN, representatives of the Canton of Geneva and representatives of the Auvergne-Rhône-Alpes region are now taking place on a regular basis.

Clearly, the strong support and cooperation of public administration services in both host states is a reassuring condition for the next steps of the FCC feasibility analysis. The recent FCC physics workshop reaffirms the interest of the physics community in the long-term scientific research programme offered by this future endeavour. The commitment of the community is the precondition for continued efforts to develop the FCC project scenario with an extended group of regional and local stakeholders. 

The post Host states gear up to work on FCC appeared first on CERN Courier.

While all eyes focus on the LHC restart, a diverse landscape of fixed-target experiments at CERN have already begun data-taking. Driven by beams from smaller accelerators in the LHC chain, they span a large range of research programmes at the precision and intensity frontiers, complementary to the LHC experiments. Several new experiments join existing ones in the new run period, in addition to a suite of test-beam and R&D facilities. 

At the North Area, which is served by proton and ion beams from the Super Proton Synchrotron (SPS), new physics programmes have been underway since the return of beams last year. Experiments in the North Area, which celebrated its 40th anniversary in 2019, are located at different secondary beamlines and span QCD, electroweak physics and QED, as well as dark-matter searches. “During Long Shutdown 2, a major overhaul of the North Area started and will continue during the next 10 years to provide the best possible beam and infrastructure for our users,” says Yacine Kadi, leader of the North Area consolidation project. “The most critical part of the project is to prepare for the future physics programme.”

The first phase of the AMBER facility at the M2 beamline is an evolution of COMPASS, which has operated since 2002 and focuses on the study of the gluon contribution to the nucleon spin structure. By measuring the proton charge radius via muon–proton elastic scattering, AMBER aims to clarify the long-standing proton–radius puzzle, offering a complementary approach to previous electron–proton scattering and spectroscopy measurements. A new data-acquisition system will enable the collaboration to measure the antiproton production cross-section to improve the sensitivity of searches for cosmic antiparticles from possible dark-matter annihilation. A third AMBER programme will concentrate on measurements of the kaon, pion and proton charge radii via Drell-Yan processes using heavy targets. 

A second North Area experiment specialising in hadron physics is NA61/SHINE, which underwent a major overhaul during Long Shutdown 2 (LS2), including the re-use of the vertex detector from the ALICE experiment. Building on its predecessor NA49, the 17 m-long NA61/SHINE facility, situated at the H2 beamline, focuses on three main areas: strong interactions, cosmic rays and cross-section measurements for neutrino physics. The collaboration continues its study of the energy dependence of hadron production in heavy-ion collisions, in which NA49 found irregularities. It also aims to observe the critical point at which the phase transition from a quark–gluon plasma to a hadron gas takes place, the threshold energy for which is only measurable at the SPS rather than at the higher energy LHC or RHIC experiments. By measuring hadron production from pion–carbon interactions, meanwhile, the team will study the properties of high-energy cosmic rays from cascades of charged particles. Finally, using kaons and pions produced from a target replicating that of the T2K experiment in Japan, NA61/SHINE will help to determine the neutrino flux composition at the future DUNE and Hyper-Kamiokande experiments for precise measurements of neutrino mixing angles and the CP-violating phase.

New physics

Situated at the same H2 beamline, the new NA65 “DsTau” experiment will study the production of D_s mesons. This is important because D_s decays are the main source of ν_τ’s in a neutrino beam, and are therefore relevant for neutrino-oscillation studies. After a successful pilot run in 2018, a measurement campaign began in 2021 to determine the ν_τ-production flux.

At the K12 secondary beamline, NA62 continues its measurement of the ultra-rare charged kaon decay to a charged pion, a neutrino and an antineutrino, which is very sensitive to possible physics beyond the Standard Model. The collaboration aims to increase its sensitivity to a level (10%) approaching theoretical uncertainties, thanks to further data and experimental improvements to the more than 200 m-long facility. One is the installation during LS2 of a muon veto hodoscope that helps to determine whether a muon is coming from a kaon decay or from other interactions. Since 2021, NA62 also operates as a beam-dump experiment, where its primary focus is to search for feebly-interacting particles. Here, the ability to determine whether muons come from the target absorber is even more important since they make up most of the background.

Dark interactions

Searching for new physics is the focus of NA64 at the H4 beamline, which studies the interaction between an electron beam and an active target to look for a hypothetical dark-photon mediator connecting the SM with a possible dark sector. With at least five times more data expected this year, and up to 10 times more data during the period of LHC Run 3, it could be possible to determine whether the dark mediator, should it exist, is either an elastic scalar or a Majorana particle. Adding further impetus to this programme is an unexpected 17 MeV peak reported in e⁺e^– internal pair production by the ATOMKI experiment and, more significantly, the tension between the measured and predicted values of the anomalous magnetic moment of the muon (g-2)_μ, for which possible explanations include models that invoke a dark mediator. During a planned muon run at the M2 beamline, the collaboration aims to cover the relevant parameter space for the (g-2)_μ anomaly.  

NA63 also receives electrons from the H4 beamline and uses a high-energy electron beam to study the behaviour of scattered electrons in a strong electromagnetic field. In particular, the experiment tests QED at higher orders, which have a gravitational analogue in extreme astroparticle physics phenomena such as black-hole inspirals and magnetars. The NA63 team will continue its measurements in June.

Besides driving the broad North Area physics programme, the SPS serves protons to AWAKE – a proof-of-principle experiment investigating the use of plasma wakefields driven by a proton bunch to accelerate charged particles. Following successful results from its first run, the collaboration aims to further develop methods to modulate the proton bunches to demonstrate scalable plasma-wakefield technology, and to prepare for the installation of a second plasma cell and an electron-beam system using the whole CNGS tunnel at the beginning of LS3 in 2026.

Located on the main CERN site, receiving beams from the Proton Synchrotron (PS), the East Area underwent a complete refurbishment during LS2, leading to a 90% reduction in its energy consumption. Its main experiment is CLOUD, which simulates the impact of particulates on cloud formation. This year, the collaboration will test a new detector component called FLOTUS, a 70 litre quartz chamber extending the simulation from a period of minutes to a maximum of 10 days. The PS also feeds the n_TOF facility, which last year marked 20 years of service to neutron science and its applications. A new third-generation spallation target installed and commissioned in 2021 will enable new n_TOF measurements relevant for nuclear astrophysics. 

Different dimensions

Taking CERN science into an altogether different dimension, the PS also links to the Antimatter Factory via the Antiproton Decelarator (AD) and ELENA rings, where several experiments are poised to test CPT invariance and antimatter gravitational interactions at increased levels of precision (see “Antimatter galore at ELENA” panel). Even closer to the proton beam source is the PS Booster, which serves the ISOLDE facility. ISOLDE covers a diverse programme across the physics of exotic nuclei and includes MEDICIS (devoted to the production of novel radioisotopes for medical research), ISOLTRAP (comprising four ion traps to measure ions) and COLLAPS and CRIS, which focus on laser spectroscopy. Its post-accelerators REX/HIE-ISOLDE increase the beam energy up to 10 MeV/u, making ISOLDE the only facility in the world that provides radioactive ion-beam acceleration in this energy range.

Antimatter galore at ELENA

Served directly by the Antiproton Decelerator (AD) for the past two decades, experiments at the CERN Antimatter Factory are now connected to the new ELENA ring, which decelerates 5.3 MeV antiprotons from the AD to 100 keV to allow a 100-fold increase in the number of trapped antiprotons. Six experiments involving around 350 researchers use ELENA’s antiprotons for a range of unique measurements, from precise tests of CPT invariance to novel studies of antimatter’s gravitational interactions. 

The ALPHA experiment focuses on antihydrogen-spectroscopy measurements, recently reaching an accuracy of two parts per trillion in the transition from the ground state to the first excited state. By clocking the free-fall of antiatoms released from a trap, it is also planning to measure the gravitational mass of antihydrogen. ALPHA’s recent demonstration of laser-cooled antihydrogen has opened a new realm of precision on anti-hydrogen’s internal structure and gravitational interactions to be explored in upcoming runs.

ASACUSA specialises in spectroscopic measurements of antiprotonic helium, recently finding surprising behaviour. The experiment is also gearing up to perform hyperfine-splitting spectroscopy in antihydrogen using atomic-beam methods complementary to ALPHA’s trapping techniques.

GBAR and AEgIS target direct measurements of the Earth’s gravitational acceleration on antihydrogen. GBAR is developing a method to measure the free-fall of antihydrogen atoms, using sympathetic laser cooling to cool antihydrogen atoms and release them, after neutralisation, from a trap directly injected with antiprotons from ELENA, maximising antihydrogen production. AEgIS, having established pulsed formation of antihydrogen in 2018, is following a different approach based on measuring the vertical drop of a pulsed cold beam of antihydrogen atoms travelling horizontally through a device called a Moiré deflectometer.

BASE uses advanced Penning traps to compare matter and antimatter with extreme precision, recently finding the charge-to-mass ratios of protons and antiprotons to be identical within 16 parts per trillion. The data also allowed the collaboration to perform the first differential test of the weak equivalence principle using antiprotons, reaching the 3% level, with experiment improvements soon expected to increase the sensitivities of both measurements. The BASE team is also working on an improved measurement of the antiproton magnetic moment, the implementation of a transportable antiproton trap called BASE-STEP and improved searches for millicharged particles.

The newest AD experiment, PUMA, which is preparing for first commissioning later this year, aims to transport trapped antiprotons collected at ELENA to ISOLDE where, from next year, they will be annihilated on exotic nuclei to study neutron densities at the surface of nuclei. 

“Thanks to the beam provided by ELENA and the major upgrades of the experiments, we hope to see big progress in ultra-precise tests of CPT invariance, first and long-awaited antihydrogen-based studies of gravity, as well as the development of new technologies such as transportable antimatter traps,” says Stefan Ulmer, head of the AD user committee. 

Stable and highly customisable beams at the North and East areas also facilitate important detector R&D and test-beam activities. These include the recently approved Water-Cherenkov Test Experiment, which will help to develop detector techniques for long-baseline neutrino experiments, and new detector components for the LHC experiments and proposed future colliders. The CERN Neutrino Platform is dedicated to the development of detector technologies for neutrino experiments across the world. Upcoming activities including ongoing contributions to the future DUNE experiment in the US, in particular the two huge DUNE cryostats and R&D for “vertical drift” liquid-argon detection technology. In the East Area, the mixed-field irradiation (CHARM) and proton-irradiation (IRRAD) facilities provide key input to detector R&D and electronics tests, similar to the services provided by the SPS-driven GIF irradiation facility and HiRadMat.

With the many physics opportunities mapped out by Physics Beyond Colliders and the consolidation of our facilities, we are looking into a bright future

Johannes Bernhard

Fixed-target experiments in the North and East areas, along with experiments at ISOLDE and the AD, demonstrate the importance of diverse physics studies at CERN, when the best path to discover new physics is unclear. Some of these experiments emerged within the Physics Beyond Colliders initiative and there are many more on the horizon, such as KLEVER and the SPS Beam Dump Facility. “With the many physics opportunities mapped out by Physics Beyond Colliders and the consolidation of our facilities, we are looking into a bright future,” says Johannes Bernhard, head of the liaison to experiments section in the beams department. “We are always aiming to serve our users with the highest beam quality and performance possible.”

The post Science diversity at the intensity and precision frontiers appeared first on CERN Courier.

Originally considered a troublesome byproduct of particle accelerators designed to explore fundamental physics, synchrotron radiation is now an indispensable research tool across a wide spectrum of science and technology. The latest generation of synchrotron-radiation sources are X-ray free electron lasers (XFELs) driven by linacs. With sub-picosecond pulse lengths and wavelengths down to the hard X-ray range, these facilities offer unprecedented brilliance, exceeding that of third-generation synchrotrons based on storage rings by many orders of magnitude. However, the high costs and complexity of XFELs have meant that there are only a few such facilities currently in operation worldwide, including the European XFEL at DESY and LCLS-II at SLAC.

CompactLight, an EU-funded project involving 23 international laboratories and academic institutions, three private companies and five third parties, aims to use emerging and innovative accelerator technologies from particle physics to make XFELs more affordable, compact, power-efficient and performant. In the early stages of the project, a dedicated workshop was held at CERN to survey the X-ray characteristics needed by the many user communities. This formed the basis for a design based on the latest concepts for bright electron photo-injectors, high-gradient X-band radio-frequency structures developed in the framework of the Compact Linear Collider (CLIC), and innovative superconducting short-period undulators. After four years of work, the CompactLight team has completed a conceptual design report describing the proposed facility in detail.

The 360-page report sets out a hard X-ray (16–0.25 keV) facility with two separate beamlines offering soft and hard X-ray sources with a pulse-repetition rate of up to 1 kHz and 100 Hz, respectively. It includes a facility baseline layout and two main upgrades, with the most advanced option allowing the operation of both soft and hard X-ray beamlines simultaneously. The technology also offers preliminary evaluations of a very compact, soft X-ray FEL and of an X-ray source based on inverse Compton scattering, considered an affordable solution for university campuses, small labs and hospitals. 

CompactLight is the most significant current effort to enable greater diffusion of XFEL facilities, says the team, which plans to continue its activities beyond the end of its Horizon 2020 contract, improving the partnership and maintaining its leadership in compact acceleration and light production. “Compared to existing facilities, for the same operating wavelengths, the technical solutions adopted ensure that the CompactLight facility can operate with a lower electron beam energy and will have a significantly more compact footprint,” explains project coordinator Gerardo D’Auria. “All these enhancements make the proposed facility more attractive and more affordable to build and operate.”

• Based on an article in Accelerating News, 4 March.

The post Compact XFELs for all appeared first on CERN Courier.

Multi-bend achromat (MBA) lattices have initiated a fourth generation for storage-ring light sources with orders of magnitude increase in brightness and transverse coherence. A few MBA rings have been built, and many others are in design or construction worldwide, including upgrades of APS and ALS in the US.

The HMBA (hybrid MBA), developed for the successful ESRF–EBS MBA upgrade has proven to be very effective in addressing the nonlinear dynamics challenges associated with pushing the emittance toward the diffraction limit. The evolution of the HMBA ring designs will be described in this seminar. The new designs are consistent with the breaking of the lattice periodicity found in traditional circular light sources, inserting dedicated sections for efficient injection and additional emittance damping.

Techniques developed for high-energy physics rings to mitigate nonlinear dynamics challenges associated with breaking periodicity at collision points were applied in the HMBA designs for the injection and damping sections. These techniques were also used to optimise the individual HMBA cell nonlinear dynamics. The resulting HMBA can deliver the long-sought diffraction limited source while maintaining the temporal and transverse stability of third-generation light sources due to the long lifetime and traditional off-axis injection enabled by nonlinear dynamics optimisation, thus improving upon the performance of rings now under construction.

Pantaleo Raimondi, professor at the Stanford Linear Accelerator Center, research technical manager, SLAC National Accelerator Laboratory and previously director, Accelerator and Source Division, ESRF.

The post Toward a diffraction limited storage-ring-based X-ray source appeared first on CERN Courier.

The overall FCC programme – comprising an electron-positron Higgs and electroweak factory (FCC-ee) as a first stage followed by a high-energy proton-proton collider (FCC-hh) – combines the two key strategies of high-energy physics. FCC-ee offers a unique set of precision measurements to be confronted with testable predictions and opens the possibility for exploration at the intensity frontier, while FCC-hh would enable further precision and the continuation of open exploration at the energy frontier. The February workshop saw advances in our understanding of the physics potential of FCC-ee, and discussions of the possibilities provided at FCC-hh and at a possible FCC-eh facility.

The overall FCC programme combines the two key strategies of high-energy physics: precision measurements at the intensity frontier and the open exploration at the energy frontier

The proposed R&D efforts for the FCC align with the requests of the 2020 update of the European strategy for particle physics and the recently published accelerator and detector R&D roadmaps established by the Laboratory Directors Group and ECFA. Key activities of the FCC feasibility study, including the development of a regional implementation scenario in collaboration with the CERN host states, were presented.

Over the past several months, a new baseline scenario for a 91 km-circumference layout has been established, balancing the optimisation of the machine performance, physics output and territorial constraints. In addition, work is ongoing to develop a sustainable operational model for FCC taking into account human and financial resources and striving to minimise its environmental impact. Ongoing testing and prototyping work on key FCC-ee technologies will demonstrate the technical feasibility of this machine, while parallel R&D developments on high-field magnets pave the way to FCC-hh.

Physics programme
A central element of the overall FCC physics programme is the precise study of the Higgs sector. FCC-ee would provide model-independent measurements of the Higgs width and its coupling to Standard Model particles, in many cases with sub-percent precision and qualitatively different to the measurements possible at the LHC and HL-LHC. The FCC-hh stage has unique capabilities for measuring the Higgs-boson self-interactions, profiting from previous measurements at FCC-ee. The full FCC programme thus allows the reconstruction of the Higgs potential, which could give unique insights into some of the most fundamental puzzles in modern cosmology, including the breaking of electroweak symmetry and the evolution of the universe in the first picoseconds after the Big Bang.

Presentations and discussions throughout the week showed the impressive breadth of the FCC programme, extending far beyond the Higgs factory alone. The large integrated luminosity to be accumulated by FCC-ee at the Z-pole enables high-precision electroweak measurements and an ambitious flavour-physics programme. While the latter is still in the early phase of development, it is clear that the number of B mesons and tau-lepton pairs produced at FCC-ee significantly surpasses those at Belle II, making FCC-ee the flavour factory of the 2040s. Ongoing studies are also revealing its potential for studying interactions and decays of heavy-flavour hadrons and tau leptons, which may provide access to new phenomena including lepton-flavour universality-violating processes. Similarly, the capabilities of FCC-ee to study beyond-the-Standard Model signatures such as heavy neutral leptons have come into further focus. Interleaved presentations on FCC-ee, FCC-hh and FCC-eh physics also further intensified the connections between the lepton- and hadron-collider communities.

The impressive potential of the full FCC programme is also inspiring theoretical work. This ranges from overarching studies on our understanding of naturalness, to concrete strategies to improve the precision of calculations to match the precision of the experimental programme.

The physics thrusts of the FCC-ee programme inform an evaluation of the run plan, which will be influenced by technical considerations on the accelerator side as well as by physics needs and the overall attractiveness and timeliness of the different energy stages (ranging from the Z pole at 91 GeV to the tt threshold at 365 GeV). In particular, the possibility for a direct measurement of the electron Yukawa coupling by extensive operation at the Higgs pole (125 GeV) raises unrivaled challenges, which will be further explored within the FCC feasibility study. The main challenge here is to reduce the spread in the centre-of-mass energy by a factor of around ten while maintaining the high luminosity, requiring a monochromatisation scheme long theorised but never applied in practice.

Detectors status and plan
Designing detectors to meet the physics requirements of FCC-ee physics calls for a strong R&D programme. Concrete detector concepts for FCC-ee were discussed, helping to establish a coherent set of requirements to fully benefit from the statistics and the broad variety of physics channels available.

The primary experimental challenge at FCC-ee is how to deal with the extremely high instantaneous luminosities. Conditions are the most demanding at the Z pole, with the luminosity surpassing 10³⁶ cm^-2s^-1 and the rate of physics events exceeding 100 kHz. Since collisions are continuous, it is not possible to employ “power pulsing” of the front-end electronics as has been developed for detector concepts at linear colliders. Instead, there is a focus on the development of fast, low-power detector components and electronics, and on efficient and lightweight solutions for powering and cooling. With the enormous data samples expected at FCC-ee, statistical uncertainties will in general be tiny (about a factor of 500 smaller than at LEP). The experimental challenge will be to minimise systematic effects towards the same level.

The mind-boggling integrated luminosities delivered by FCC-ee would allow Standard Model particles – in particular the W, Z and Higgs bosons and the top quark, but also the b and c quarks and the tau lepton – to be studied with unprecedented precision. The expected number of Z bosons produced (5×10¹²) is more than five orders of magnitude larger than the number collected at LEP, and more than three orders of magnitude larger than that envisioned at a linear collider. The high-precision measurements and the observation of rare processes made possible by these large data samples will open opportunities for new-physics discoveries, including the direct observation of very weakly-coupled particles such as heavy-neutral leptons, which are promising candidates to explain the baryon asymmetry of the universe.

With overlapping requirements, designs for FCC-ee can follow the example of detectors proposed for linear colliders.

The detectors that will be located at two (possibly four) FCC-ee interaction points must be designed to fully profit from the extraordinary statistics. Detector concepts under study feature: a 2 T solenoidal magnetic field (limited in strength to avoid blow-up of the low-emittance beams crossing at 30 mrad); a small-pitch, thin-layers vertex detector providing an excellent impact-parameter resolution for lifetime measurements; a highly transparent tracking system providing a superior momentum resolution; a finely segmented calorimeter system with excellent energy resolution for electrons and photons, isolated hadrons and jets; and a muon system. To fully exploit the heavy-flavour possibilities, at least one of the detector systems will need efficient particle-identification capabilities allowing π/K separation over a wide momentum range, for which there are ongoing R&D efforts on compact, light RICH detectors.

With overlapping requirements, designs for FCC-ee can follow the example of detectors proposed for linear colliders. The CLIC-inspired CLD concept – featuring a silicon-pixel vertex detector and a silicon tracker followed by a 3D-imaging, highly granular calorimeter system (a silicon-tungsten ECAL and a scintillator-steel HCAL) surrounded by a superconducting solenoid and muon chambers interleaved with a steel return yoke – is being adapted to the FCC-ee experimental environment. Further engineering effort is needed to make it compatible with the continuous-beam operation at FCC-ee. Detector optimisation studies are being facilitated by the robust existing software framework which has been recently integrated into the FCC study.

The IDEA (International Detector for Electron-positron Accelerator) concept, specifically developed for a circular electron-positron collider, brings in alternative technological solutions. It includes a five-layer vertex detector surrounded by a drift chamber, enclosed in a single-layer silicon “wrapper”. The distinctive element of the He-based drift chamber is its high transparency. Indeed, the material budget of the full tracking system, including the vertex detector and the wrapper, amounts to only about 5% (10%) of a radiation length in the barrel (forward) direction. The drift chamber promises superior particle-identification capabilities via the use of a cluster-counting technique that is currently under test-beam study. In the baseline design, a thin low-mass solenoid is placed inside a monolithic, 2 m-deep, dual-readout fibre calorimeter. An alternative (more expensive) design also features a finely segmented crystal ECAL placed immediately inside the solenoid, providing an excellent energy resolution for electrons and photons.

Recently, work has started on a third FCC-ee detector concept comprising: a silicon vertex detector; a light tracker (drift chamber or full-silicon device); a thin, low-mass solenoid; a highly-granular noble liquid-based ECAL; a scintillator-iron HCAL; and a muon system. The current baseline ECAL design is based on lead/steel absorbers and active liquid-argon, but a more compact option based on tungsten and liquid-krypton is an interesting option. The concept design is currently being implemented inside the FCC software framework.

All detector concepts are under evolution and there is ample room for further innovative concepts and ideas.

Closing remarks
Circular colliders reach higher luminosities than linear machines because the same particle bunches are used over many turns, while detectors can be installed at several interaction points. The FCC-ee programme greatly benefits from the possibility of having four interaction points to allow the collection of more data, systematic robustness and better physics coverage — especially for very rare processes that could offer hints as to where new physics could lie. In addition, the same tunnel can be used for an energy-frontier hadron collider at a later stage.

The FCC feasibility study will be submitted by 2025, informing the next update of the European strategy for particle physics. Such a machine could start operation at CERN within a few years after the full exploitation of the HL-LHC in around 2040. CERN, together with its international partners, therefore has the opportunity to lead the way for a post-LHC research infrastructure that will provide a multi-decade research programme exploring some of the most fundamental questions in physics. The geographical distribution of participants in the 5^th FCC physics workshop testifies to the global attractiveness of the project. In addition, the ongoing physics and engineering efforts, the cooperation with the host states, the support from the European physics community and the global cooperation to tackle the open challenges of this endeavour, are reassuring for the next steps of the FCC feasibility study.

The post Spotlight on FCC physics appeared first on CERN Courier.

Several technologies are being developed for this High-Luminosity LHC (HL-LHC) upgrade. One is new, large-aperture quadrupole magnets based on a niobium-tin superconductor. These will be installed on either side of the ATLAS and CMS experiments, providing the space required for smaller beam-spot sizes at the interaction points and shielding against the higher radiation levels when operating at increased luminosities. The other key technology, necessary to take advantage of the smaller beam-spot size at the interaction points, is a series of superconducting radio-frequency (RF) “crab” cavities that enlarge the overlap area of the incoming bunches and thus increase the probability of collisions. Never used before at a hadron collider, a total of 16 compact crab cavities will be installed on either side of each of ATLAS and CMS once Run 3 ends and Long Shutdown 3 begins.

At a collider such as the LHC, it is imperative that the two counter-circulating beams are physically separated by an angle, aka the crossing angle, such that bunches collide only in one single location over the common interaction region (where the two beams share the same beam pipe). The bunches at the HL-LHC will be 10 cm long and only 7 μm wide at the collision points, resembling thin long wires. As a result, even a very small angle between the bunches implies an immediate loss in luminosity. With the use of powerful superconducting crab cavities, the tilt of the bunches at the collision point can be precisely controlled to make it optimal for the experiments and fully exploit the scientific potential of the HL-LHC.

Radical concepts 

The tight space constraints from the relatively small separation of the two beams outside the common interaction region requires a radically new RF concept for particle deflection, employing a novel shape and significantly smaller cavities than those used in other accelerators. Designs for such devices began around 10 years ago, with CERN settling on two types: double quarter wave (DQW) and RF-dipole (RFD). The former will be fitted around CMS, where bunches are separated vertically, and the latter around ATLAS, where bunches will be separated horizontally, requiring crab cavities uniquely designed for each plane. It is also planned to swap the crossing-angle planes and crab-cavity installations at a later stage during the HL-LHC operation.

In 2017, two prototype DQW-type cavities were built and assembled at CERN into a special cryomodule and tested at 2 K, validating the mechanical, cryogenic and RF functioning. The module was then installed in the Super Proton Synchrotron (SPS) for beam tests, with the world’s first “crabbing” of a proton beam demonstrated on 31 May 2018. In parallel, the fabrication of two prototype RFD-type cavities from high-purity niobium was underway at CERN. Following the integration of the devices into a titanium helium tank at the beginning of 2021, and successful tests at 2 K reaching voltages well beyond the nominal value of 3.4 MV, the cavities were equipped with specially designed RF couplers, which are necessary for beam operations. The two cavities are now being integrated into a cryomodule at Daresbury Laboratory in the UK as a joint effort between CERN and the UK’s Science and Technology Facilities Council (STFC). The cryomodule will be installed in a 15 m-long straight section (LSS6) of the SPS in 2023 for its first test with proton beams. This location in the SPS is equipped with a special by-pass and other services, which were put in place in 2017–2018 to test and operate the DQW-type module. 

The manufacturing challenge 

Due to the complex shape and micrometric tolerances required for the HL-LHC crab cavities, a detailed study was performed to realise the final shape through forming, machining, welding and brazing operations on the high-purity niobium sheets and associated materials (see “Fine machining” images). To ensure a uniform removal of material along the cavities’ complex shape, a rotational buffer chemical polishing (BCP) facility was built at CERN for surface etching of the HL-LHC crab cavities. For the RFD and DQW, the rotational setup etches approximately 250 μm of the internal RF surface to remove the damaged cortical layer during the forming process. Ultrasound measurements were performed to follow the evolution of the cavity-wall thickness during the BCP steps, showing remarkable uniformity (see “Chemical etching” images).

Preparation of the RFD cavities involved a similar process as that for the DQW modules. Following chemical etching and a very high-temperature bake at 650 °C in a vacuum furnace, the cavities are rinsed in ultra-pure water at high pressure (100 bar) for approximately seven hours. This process has proven to be a key step in the HL-LHC crab-cavity preparation to enable extremely high fields and suppress electron-field emitters, which can limit the performance. The cavity is then closed with its RF ancillaries in an ISO4 cleanroom environment to preserve the ultra-clean RF surface, and installed into a special vertical cryostat to cool the cavity surface to its 2 K operating temperature (see “Clean and cool” image, top). Both RFD cavities reached performances well above the nominal target of 3.4 MV. RFD1 reached more than 50% over the nominal voltage and RFD2 reached above a factor of two (7 MV) – a world-record deflecting field in this frequency range. These performances were reproducible after the assembly and welding of the helium tank owing to the careful preparation of the RF surface throughout the different steps of assembly and preparation. 

The helium tank provides a volume around the cavity surface that is maintained at 2 K with superfluid helium (see “Clean and cool” image, bottom). Due to sizeable deformations during the cool-down process from ambient temperature, a titanium vessel which has a thermal behaviour close to that of the niobium cavity is used. A magnetic shield between the cavity and the helium tank suppresses stray fields in the operating environment and further preserves cavity performance. Following the tests with helium tanks, the cavities were equipped with higher-order-mode couplers and field antennae to undergo a final test at 2 K before cryostating them into a two-cavity string.

The crab cavities require many ancillary components to allow them to function. This overall system is known as a cryomodule (see “Cryomodule” image, top) and ensures that the operational environment is correct, including the temperature, stability, vacuum conditions and RF frequency of the cavities. Technical challenges arise due to the need to assemble the cavity string in an ISO4 cleanroom, the space constraints of the LHC (leading to the rectangular compact shape), and the requirement of fully welded joints (where typically “O” rings would be used for the insulation vacuum).

Design components

The outer vacuum chamber (OVC) of the cryomodule provides an insulation vacuum to prevent heat leaking to the environment as well as providing interfaces to any external connections. Manufactured by ALCA Technology in Italy, the OVC used a rectangular design where the cavity string is mounted to a top-plate that is lowered into the rest of the OVC, and includes four large windows to allow access for repair in situ if required (see “Cryomodule” image, bottom). Since the first DQW prototype module, several cryomodule interfaces including cryogenic and vacuum components were updated to be fully compatible with the final installation in the HL-LHC. 

The HL-LHC crab-cavity programme has developed into a mature project supported by a large number of collaborating institutions around the world

Since superconducting RF cavities can have a higher surface resistance if cooled below their transition temperature in the presence of a magnetic field, they need to be shielded from Earth’s magnetic field and stray fields in the surrounding environment. This is achieved using a warm magnetic shield manufactured in the OVC, and a cold magnetic shield mounted inside the liquid-helium vessel. Both shields, which are made from special nickel-iron alloys, are manufactured by Magnetic Shields Ltd in the UK.

Status and outlook

The RFD crab-cavity pre-series cryomodule will be assembled this year at Daresbury lab, where the infrastructure on site has been upgraded, including an extension to the ISO4 cleanroom area and the introduction of an ISO6 preparation area. A bespoke five-tonne crane has also been installed and commissioned to allow the precise lowering of the delicate cavity string into the outer vacuum vessel.

Parallel activities are taking place elsewhere. The HL-LHC crab-cavity programme has developed into a mature project supported by a large number of collaborating institutions around the world. In the US, the Department of Energy is supporting the HL-LHC Accelerator Upgrade Project to coordinate the efforts and leverage the expertise of a group of US laboratories and universities (FNAL, BNL, JLAB, SLAC, ODU) to deliver the series RFD cavities for the HL-LHC. In 2021, two RFD prototype cavities were built by the US collaboration and exceeded the two most important functional project requirements for crab cavities – deflecting voltage and quality factor. After this successful demonstration, the fabrication of the pre-series cavities was launched.

Crab cavities were first implemented in an accelerator in 2006, at the KEKB electron–positron collider in Japan, where they helped the collider reach record luminosities. A different “crab-waist” scheme is currently employed at KEKB’s successor, SuperKEKB, helping to reach even higher luminosities. The development of ultra-compact, very-high-field cavities for a high-energy hadron collider such as the HL-LHC is even more challenging, and will be essential to maximise the scientific output of this flagship facility beyond the 2030s. 

Beyond the HL-LHC, the compact crab-cavity concepts have been adopted by future facilities, including the proton–proton stage of the proposed Future Circular Collider; the Electron–Ion Collider under construction at Brookhaven; bunch compression in synchrotron X-ray sources to produce shorter pulses; and ultrafast particle separators in proton linacs to separate bunches of secondary particles for different experiments. The full implementation of this technology at the HL-LHC is therefore keenly awaited. 

The post Crab cavities enter next phase appeared first on CERN Courier.

The world’s longest-serving heavy-ion collider, the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory, started its latest run in December. In addition to further probing the quark–gluon plasma, the focus of RHIC Run 22 (the 3.8 km-circumference collider’s 22nd run in as many years) is on testing innovative accelerator techniques and detector technologies for the Electron–Ion Collider (EIC) due to enter operation at Brookhaven in the early 2030s.

The EIC, which will add an electron storage ring to RHIC, will collide 5–18 GeV electrons (and possibly positrons) with ion beams of up to 275 GeV per nucleon, targeting luminosities of 10³⁴ cm^–2 s^–1 and a beam polarisation of up to 85%. This will enable researchers to go beyond the present one-dimensional picture of nuclei and nucleons: by correlating the longitudinal components of the quark and gluon momenta with their transverse momenta and spatial distribution inside the nucleon, the EIC will enable 3D “nuclear femtography”.

Unique ability

Preparations for the EIC rely on RHIC’s unique ability to collide polarised proton beams via the use of helical dipole magnets, which offers a directional frame of reference to study hadron collisions. The last time polarised protons were collided at RHIC was 2017. For Run 22, the accelerator team aims to accumulate proton–proton collisions at the highest possible polarisation, and also at the highest energies (255 GeV per beam). To ensure the EIC hadron beams are as tightly packed as possible, thus maximising the luminosity, the accelerator team will try a technique previously used at RHIC to accelerate larger particles, but which has never been used with protons before.

“We are going to split each proton bunch into two when they’re still at low energy in the Booster, and accelerate those as two separate bunches,” explains Run-22 coordinator Vincent Schoefer. “That splitting will alleviate some of the stress during low energy, and then we can merge the bunches back together to put very dense bunches into RHIC.” Such merging is challenging, he adds, because it takes around 300,000 turns in the Alternating Gradient Synchrotron (the link between the Booster and RHIC), during which the protons must be handled “very gently”.

To further reduce the spread of high-energy hadron beams, the team will explore several cooling strategies (a major challenge for high-energy hadron beams) for possible use at the EIC. One is coherent electron cooling, whereby electrons from a high-gain free-electron laser are used to attract the protons closer to a central position. In addition, the team plans to ramp up beams of helium-3 ions to develop methods for measuring the polarisation of particles other than protons. Measuring how particles in the beam scatter off a gas target is the established method, but ions such as helium-3 can complicate matters by breaking up when they strike the target. To accurately measure the polarisation of helium-3 and other beams at the EIC, it is necessary to identify when this breakup occurs. During Run 22 the RHIC team will test its ability to accurately characterise scattering products using unpolarised helium-3 beams to develop new polarimetry methods.

During the run, RHIC’s recently upgraded STAR detector will track particles emerging from collisions at a wider range of angles than ever before (covering a rapidity of –1.5 – 4.2). The upgrades include finer granulated sensors for the inner part of the time projection chamber, and two new forward-tracking detectors and electromagnetic and hadronic calorimetery at one end of the detector, which will allow better reconstruction of jets.

Detector technologies

In addition to increasing the dataset for exploring colour-charge interactions, these upgrades will give physicists crucial information about the detector technologies and the behaviour of nucleon structure relevant to the EIC. RHIC’s other main detector, the upgraded PHENIX, is under construction and scheduled to enter operation during Run 23 next year.

“Our goal this run is basically doing EIC physics with proton–proton collisions,” says Elke-Caroline Aschenauer, who led the STAR upgrade project. “We have to verify that what you measure in electron–proton collisions at the EIC and in proton–proton events at RHIC is universal – meaning it doesn’t depend on which probe you use to measure it.”

The post RHIC stress-tests the future EIC appeared first on CERN Courier.

The successful restart of Linac4 on 9 February marked the start of the final countdown to LHC Run 3. Inaugurated in May 2017 after two decades of design and construction, Linac4 was connected to the next link in the accelerator chain, the Proton Synchrotron Booster (PSB), in 2019 at the beginning of Long Shutdown 2 and operated for physics last year. The 86 m-long accelerator now replaces the long-serving Linac2 as the source of all proton beams for CERN experiments.

On 14 February, H^– ions accelerated to 160 MeV in Linac4 were sent to the PSB, with beam commissioning and physics to start in ISOLDE on 7 and 28 March. Beams will be sent to the PS on 28 February, to serve, after set-up, experiments in the East Area, the Antiproton Decelerator and n_TOF. The SPS will be commissioned with beam during the week beginning 7 March, after which beams will be supplied to the AWAKE facility and to the North Area experiments, where physics operations are due to begin on 25 April.

Meanwhile, preparations for some of the protons’ final destination, the LHC, are under way. Powering tests and magnet training in the last of the LHC’s eight sectors are scheduled to start in the week of 28 February and to last for four weeks, after which the TI12 and TI18 transfer tunnels and the LHC experiments will be closed and machine checkout will begin. LHC beam commissioning with 450 GeV protons is scheduled to start on 11 April, with collisions at 450 GeV per beam expected around 10 May. Stable beams with collisions at 6.8 TeV per beam and nominal bunch population are scheduled for 15 June. An intensity ramp-up will follow, producing collisions with 1200 bunches per beam in the week beginning 18 July on the way to over double this number of bunches. High-energy proton-proton operations will continue for 3–4 months, before the start of a month-long run with heavy ions on 14 November. All dates are subject to change as the teams grapple with LHC operations at higher luminosities and energies than those during Run 2, following significant upgrade and consolidation work completed during LS2.

Among the highlights of Run 3 are the first runs of the neutrino experiments FASERν and SND@LHC

Among the highlights of Run 3 are the first runs of the neutrino experiments FASERν and SND@LHC, as well as the greater integrated luminosities and physics capabilities resulting from upgrades of the four main LHC experiments. A special request was made by LHCb for a SMOG2 proton-helium run in 2023 to measure the antiproton production rate and thus improve understanding of the cosmic antiproton excess reported by AMS-02. Ion runs with oxygen, including proton-oxygen and oxygen-oxygen, will commence in 2023 or 2024. The former is also long-awaited by the cosmic-ray community, to help improve models of high-energy air showers, while high-energy oxygen-oxygen collisions allow studies of the emergence of collective effects in small systems. High β* runs to maximise the interaction rate will be available for the forward experiments TOTEM and LHCf in late 2022 and early 2023.

On 28 January, CERN announced a change to the LHC schedule to allow necessary work for the High-Luminosity LHC (HL-LHC) both in the machine and in the ATLAS and CMS experiments. The new schedule foresees Long Shutdown 3 to start in 2026, one year later than in the previous schedule, and to last for three instead of 2.5 years. “Although the HL-LHC upgrade is not yet completed, a gradual intensity increase from 1.2 × 10¹¹ to 1.8 × 10¹¹ protons per bunch is foreseen for 2023,” says Rende Steerenberg, head of the operations group. “This promises exciting times and a huge amount of data for the experiments.”

The post LHC Run 3: the final countdown appeared first on CERN Courier.

Bruno Touschek was born in Vienna on 3 February 1921. His mother came from a well-to-do Jewish family and his father was a major in the Austrian Army. Bruno witnessed the tragic consequences of racial discrimination that prevented him from both completing his high school and university studies in Austria. But he also experienced the hopes of the post-war era and played a role in the post-war reconstruction.  With the help of his friends, he continued his studies in Hamburg, where he worked on the 15 MeV German betatron proposed by Rolf Widerøe and learnt about electron accelerators. After the war he obtained his PhD at the University of Glasgow in 1949 , where he was involved in theoretical studies and in the building of a 300 MeV electron synchrotron. Touschek emerged from the early-post war years as one of the first physicists in Europe endowed with a unique expertise in the theory and functioning of accelerators. His genius was nurtured by close exchanges with Arnold Sommerfeld, Werner Heisenberg, Max Born and Wolfgang Pauli, among others, and flourished in Italy, where he arrived in 1953 called by Edoardo Amaldi, his first biographer and first Secretary-General of CERN.

In 1960 he proposed and built the first electron-positron storage ring, Anello di Accumulazione (AdA), which started operating in Frascati in February 1961. The following year, in order to improve the injection efficiency, a Franco-Italian collaboration was born that brought AdA to Orsay. It was here that the “Touschek effect“, describing the loss and scattering of charged particles in storage rings, was discovered and the proof of collisions in an electron-positron ring was obtained.

AdA paved the way to the electron-positron colliders ADONE in Italy, ACO in France, VEPP-2 in the USSR and SPEAR in the US. Bruno spent the last year of his life at CERN, from where – already quite ill – he was brought to Innsbruck, Austria, where he passed away on 25 May 1978 aged just 57.

Bruno Touschek’s  life and scientific contributions were celebrated at a memorial symposium from 2 to 4 December, held in the three institutions where Touschek has left a lasting legacy: Sapienza University of Rome, INFN Frascati National Laboratories and Accademia Nazionale dei Lincei. Contributions also came from the Irène Joliot-Curie Laboratoire, and sponsorship from the Austrian Embassy in Italy.

In addition to Touschek’s impact on the physics of particle colliders, the three-day symposium addressed the present-day landscape. Carlo Rubbia and Ugo Amaldi gave a comprehensive overview of the past and future of particle colliders, followed by talks about physics at ADONE and LEP, and future machines, such as a muon collider, the proposed Future Circular Collider at CERN and the Circular Electron Positron Collider in China, as well as new developments in accelerator techniques. ADONE’s construction challenges were remembered. Developments in particle physics since the 1960s – including the quark model, dual models and string theory, spontaneous symmetry breaking and statistical physics – were described in testimonies from the  universities of Rome, Frascati, Nordita and Collège de France.

Touschek’s direct influence was captured in talks by his former students, from Rome and the Frascati theory group, which he founded in the mid 1960s. His famous lectures on statistical mechanics, given from 1959 to 1960, were remembered by many speakers. Giorgio Parisi, who graduated with Nicola Cabibbo, recollected the years in Frascati after the observation of a large hadron multiplicity in e⁺ e^– annihilations made by ADONE, and the ideas leading to QCD.

The final day of the symposium, which took place at the Accademia dei Lincei where Touschek had been a foreign member since 1972, turned to future strategies in high-energy physics, including neutrinos and other messengers from the universe. Also prominent were the many benefits brought to society by particle accelerators, reaffirming the intrinsic broader value of fundamental research.

Touschek’s life and scientific accomplishments have been graphically illustrated in the three locations of the symposium, including displays of his famous drawings on academic life in Roma and Frascati. LNF’s visitor center was dedicated to Touschek, in the presence of his son Francis Touschek.

The post Commemorating Bruno Touschek’s centenary appeared first on CERN Courier.

Within a particle accelerator, the surface of materials directly exposed to the beams interacts with the circulating particles and, in so doing, influences the local vacuum conditions through which those particles travel. Put simply: accelerator performance is linked inextricably to the surface characteristics of the vacuum beam pipes and chambers that make up the machine. 

In this way, the vacuum vessel’s material top surface and subsurface layer (just a few tens of nm thick) determine, among many other characteristics, the electrical resistance of the beam image current, synchrotron light reflectivity, degassing rates and secondary electron yield under particle bombardment. The challenge for equipment designers and engineers is that while the most common structural materials used to fabricate vacuum systems – stainless steel, aluminium alloys and copper – ensure mechanical resistance against atmospheric pressure, they do not deliver the full range of chemical and physical properties required to achieve the desired beam performance. 

Sputtering is one of the methods used to produce thin films by physical vapour deposition

Aluminium alloys, though excellent in terms of electrical conductivity, suffer from high secondary electron emission. On the latter metric, copper represents a better choice, but can be inadequate regarding gas desorption and mechanical performance. Even though it is the workhorse of vacuum technology, for its excellent mechanical and metallurgical behaviour, stainless steel lacks most of the required surface properties. The answer is clear: adapt the surface properties of these structural materials to the specific needs of the accelerator environment by coating them with more suitable materials, typically using electrochemical or plasma treatments. (For a review of electrochemical coating methods, see Surface treatment: secrets of success in vacuum science.) 

Variations on the plasma theme

The emphasis herein is exclusively on plasma-based thin-film deposition, in which an electrically quasi-neutral state of matter (composed of positive and negative charged particles) is put to work to re-engineer the physical and chemical properties of vacuum component/subsystem surfaces. A plasma can be produced by ionising gas atoms so that the positive charges are ions, and the negative ones are electrons. The most useful properties of the resultant gas plasma derive from the large difference in inertial mass between the particles carrying negative and positive charges. Owing to their much lower inertial mass, electrons are a lot more responsive than ions to variations of the electromagnetic field, leading to separation of charges and electrical fields within the plasma. What’s more, the particle trajectories for ions and electrons also differ markedly. 

These characteristics can be exploited to deposit thin films and, more generally, to modify the properties of vacuum chamber and component surfaces. For such a purpose, noble-gas ions are extracted from a plasma and accelerated towards a negatively charged solid target. If the ions acquire enough kinetic energy (of the order of hundreds to thousands of eV), one of the effects of the bombardment is the extraction of neutral atoms from the target and their deposition on the surface of the substrate to be modified. This mechanism – called sputtering – is one of the methods used to produce thin films by physical vapour deposition (PVD), where film materials are extracted from a solid into a gas phase before condensing on a substrate.

In the plasma, the lost ions are reintroduced by electron ionisation of additional gas atoms. While the rate of ionisation is improved by increasing the gas density, an excessive gas density can have a detrimental effect on the sputtered atoms (as their trajectories are modified and their kinetic energy decreased by multiple collisions with gas atoms). The alternative is to increase the length of the electron trajectories by applying a magnetic field of several hundred gauss to the plasma. 

Contrary to ions – which are affected minimally – electrons move around the lines of force of the magnetic field in longer helical-like curves, such that the probability of hitting an atom is higher. As electrons are sooner or later lost – either on the growing film or nearby surfaces – the plasma is refilled by secondary electrons extracted from the target (as a result of ion collisions). For a given set of parameters – among them target voltage, plasma power, gas pressure and magnetic flux density – the plasma ultimately attains stable conditions and a constant rate of deposition. Typical film thicknesses for accelerator applications range from a few tens of nm to 2–3 microns.

Unique requirements

The peculiarities of thin-film deposition for accelerator applications lie in the size of the objects to be coated and the purity of the coatings in question. Substrate areas, for example, range from a few cm² up to m², and in a great variety of 3D shapes and geometries. Large-aspect-ratio beam pipes that are several metres long or complicated multicell cavities for RF applications are typical substrates regularly coated at CERN. The coating process is implemented either in dedicated workshops or directly inside the accelerators during the retrofitting of installed equipment. 

HiPIMS target geometries and coating parameters must be optimised for each family of accelerator components 

The simplest sputtering configuration can be deployed when coating a cylindrical beam pipe. The target, which is made of a wire or a rod of the material to be deposited, is aligned along the longitudinal axis of the beam pipe. Argon is the most commonly used noble gas, at a pressure that depends on the cross-section – i.e. the smaller the diameter, the higher the pressure (a typical value for vacuum chambers that are a few centimetres in diameter is 0.1 mbar). The plasma is ignited by polarising the target negatively (at a few hundred volts) using a DC power supply while keeping the pipe grounded. It’s possible to reduce the pressure by one or two orders of magnitude if a magnetic field is applied parallel to the target (owing to the longer electron paths). In this case, the deposition technique is known as DC magnetron sputtering. 

When the substrate is not a simple cylinder, however, the target design becomes more complicated. That’s because of the need to accommodate different target–substrate distances, while the angle of incidence of sputtered atoms on the substrate is also subject to change. As a result, the deposited film might have different thicknesses and uneven properties at different locations on the substrate (owing to dissimilar morphologies, densities and defects, including voids). These weaknesses have been addressed, in large part, over recent years with a new family of sputtering methods called high-power impulse magnetron sputtering (HiPIMS). 

In HiPIMS, short plasma pulses (of the order of 10-100 μs) of high power density (kW/cm² regime) are applied to the target. The discharge is shut down between two consecutive pulses for a duration of about 100–1000 μs; in this way, the duty cycle is low (less than 10%) and the average power ensures there is no overheating and deformation of the target. The resulting plasma, though, is about 10 times denser (approximately 10¹³ ions/cm³) versus standard DC magnetron sputtering – a figure of merit that, thanks to a bias voltage applied to the substrate, ensures a higher fraction of ionised sputtered atoms are transported to the surfaces to be coated. 

The impingement of such energetic ions produces denser films and reduces the columnar structure resulting from the deposition of sputtered atoms moving along lines of sight. As the bias voltage is not always a safe and practical solution, the CERN vacuum team has successfully tested the application of a positive pulse to the target immediately after the main negative pulse. The effect is an increase in energy of the ionised sputtered atoms, with equivalent results as per the bias voltage (though with a simpler implementation for accelerator components).  

Owing to the variety of materials and shapes encountered along a typical (or atypical) beamline, the HiPIMS target geometries and coating parameters must be optimised for each distinct family of accelerator components. This optimisation phase is traditionally experimental, based on testing and measurement of “coupon samples” and then prototypes. In the last five years, however, the CERN team has reinforced these experimental studies with 3D simulations based on a particle-in-cell Monte Carlo/direct simulation Monte Carlo (PICMS/DSMC) code – a capability originally developed at the Fraunhofer Institute for Surface Engineering and Thin Films (IST) in Braunschweig, Germany. 

Plasma versatility

So much for the fundamentals of plasma processing, what of the applications? At CERN, the large-scale deployment of thin-film coatings began in the 1980s on the Large Electron–Positron (LEP) collider. To increase LEP’s collision energy to 200 GeV and above, engineering teams studied, and subsequently implemented, superconducting niobium (Nb) thin films deposited on copper (Cu) for the RF cavities (in place of bulk niobium). 

This technology was also adopted for the Large Hadron Collider (LHC), the High Intensity and Energy ISOLDE (HIE ISOLDE) project at CERN and other European accelerators operating at fields up to 15 MV/m. The advantages are clear: lower cost, better thermal stability (thanks to the higher thermal conductivity of the copper substrate), and reduced sensitivity to trapped magnetic fields. The main drawback of Nb/Cu superconducting RF cavities is an exponential growth of the power lost in an RF cycle with the accelerating electrical field (owing to resistivity and magnetic permeability of the Nb film). This weakness, although investigated extensively, has eluded explanation and proposed mitigation for the past 20 years. 

NEG coatings comprise a mixture of titanium, zirconium and vanadium

It’s only lately, in the frame of studies for the proposed electron–positron Future Circular Collider (FCC-ee), that researchers have shed light on this puzzling behaviour. Those insights are due, in large part, to a deeper theoretical analysis of Nb thin-film densification as a result of HiPIMS, though a parallel line of investigation involves the manufacturing of seamless copper cavities and their surface electropolishing. In both cases, the objective is the reduction of defects in the substrate to enhance film adherence and purity. 

Related studies have shown that Nb films on Cu can perform as well as bulk Nb in terms of superconducting RF properties, though coating materials other than Nb are also under investigation. Today, for example, the CERN vacuum group is evaluating Nb₃Sn and V₃Si – both of which are part of the A15 crystallographic group and exhibit superconducting transition temperatures of about 18 K (i.e. 9 K higher than Nb). This higher critical temperature would allow the use of RF cavities operating at 4.3 K (instead of 1.9 K), yielding significant simplification of the cryogenic infrastructure and reductions in electrical energy consumption. Even so, intense development is still necessary before these coatings can really challenge pure Nb films – not least because A15 films are brittle, plus the coating of such materials is tricky (given the need to reproduce a precise stoichiometry and crystallographic structure). 

Game-changing innovations

Another wide-scale application of plasma processing at CERN is in the deposition of non-evaporable-getter (NEG) thin-film coatings, specialist materials originally developed to provide distributed vacuum pumping for the LHC. NEG coatings comprise a mixture of titanium, zirconium and vanadium with a typical composition around 30:30:40, respectively. For plasma deposition of NEG films, the target (comprising three interlacing elemental wires) is pulled along the main axis of the beam pipes. Once the coated vacuum chambers are installed within an accelerator and pumped out, the NEG films undergo heating for 24 hours at temperatures ranging from 180 to 250 °C – a process known as activation, in which the superficial oxide layer and any contaminants are dissolved into their bulk. 

The clean surfaces obtained in this way chemically adsorb most of the gas species in the vacuum system at room temperature – except for noble gases (which are chemically inert) and methane (for which small auxiliary pumps are necessary). The NEG-coated surfaces provide an impressively high pumping speed and, thanks to their cleanliness, a lower desorption yield when bombarded by electrons, photons and ions – and all this with minimal space occupancy. Moreover, owing to their maximum secondary electron yields (δ_max) below 1.3, NEG coatings avoid the development of electron multipacting, the main cause of electron clouds in beam pipes (and related unfavourable impacts on beam performance, equipment operation and cryogenic heat load). 

More broadly, plasma processing of NEG coatings represents a transformative innovation in the implementation of large-scale vacuum systems. Hundreds of beam pipes were NEG-coated for the long straight section of the LHC, including the experimental vacuum chambers inserted in the four gigantic detectors. Beyond CERN, NEG coatings have also been employed widely in other large scientific instruments, including the latest generation of synchrotron light sources.

In-situ capabilities

Of course, NEG coatings require thermal activation, so cannot be applied in vacuum systems that are unheatable (i.e. vacuum vessels that operate at cryogenic temperatures or legacy accelerators that may need retrofitting). For these specific cases, the CERN vacuum team has, over the past 15 years, been developing and iterating low-δ_max carbon coatings comprised mostly of amorphous carbon (a-C) with prevailing graphitic-like bonding among the carbon atoms. 

Even though a-C thin films were originally studied for CERN’s older Super Proton Synchrotron (SPS), they are now the baseline solution for the beam screen of the superconducting magnets in the long straight section of the High-Luminosity LHC. A 100 nm thin coating is deposited either in the laboratory for the new magnets (located on both sides of the ATLAS and CMS detectors) or in situ for the ones already installed in the tunnel (both sides of LHCb and ALICE). 

Production of denser plasmas will be key for future applications in surface treatments for accelerators

The in situ processing has opened up another productive line of enquiry: the possibility of treating the surface of beam screens (15 m long, a few cm diameter) directly in the accelerators with the help of mobile targets. The expectation is that these innovative coating methods for a-C could, over time, also be applied to improve the performance of installed vacuum chambers in the LHC’s arcs, without the need to dismount magnets and cryogenic connections. 

Opportunity knocks

Looking ahead, the CERN vacuum team has plenty of ideas regarding further diversification of plasma surface treatments – though the direction of travel will ultimately depend on the needs of future studies, projects and collaborations. Near term, for example, there are possible synergies with the Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE), an accelerator R&D project based at CERN that’s investigating the use of plasma wakefields driven by a proton bunch to accelerate charged particles over short distances. Certainly, the production of denser plasmas (and their manipulation) will be key for future applications in surface treatments for accelerators. 

Another area of interest is the use of plasma-assisted chemical vapour deposition to extend the family of mat­erials that can be deposited. For the longer term, the coating of vacuum systems with inert materials that allow the attainment of very low pressures (in the ultrahigh vacuum regime) in a short timeframe (five years) without bakeout remains one of the most ambitious targets.

The post Plasmas on target in vacuum science appeared first on CERN Courier.

The reliability of the CERN vacuum systems is very much front-and-centre as the restart of the LHC physics programme approaches in mid-2022. The near-term priority is the recommencement of beam circulation in vacuum systems that were open to the air for planned interventions and modification – sometimes for several days or weeks – during Long Shutdown 2 (LS2), a wide-ranging overhaul of CERN’s experimental infrastructure that’s been underway since the beginning of 2019.  

With LS2 now drawing to a close and pilot beam already circulated in October for a general check of the accelerator chain, it’s worth revisiting the three operational objectives that CERN’s engineering teams set out to achieve during shutdown: consolidation of the LHC dipole diodes (essential safety elements for the superconducting magnets); the anticipation of several interventions required for the High-Luminosity LHC (HL–LHC) project (the successor to the LHC, which will enter operation in 2028); and the LHC Injectors Upgrade project to enhance the injection chain so that beams compatible with HL–LHC expectations can be injected into CERN’s largest machine. 

“The CERN vacuum team has made fundamental contributions to the achievement of the LS2 core objectives and other parallel activities,” notes Paolo Chiggiato, head of the CERN vacuum, surfaces and coatings group. “As such, we have just completed an intense period of work in the accelerator tunnels and our laboratories, as well as running and supporting numerous technical workshops.” 

As for vacuum specifics, all of the LHC’s arcs were vented to the air after warm-up to room temperature; all welds were leak-checked after the diode consolidation (with only one leak found among the 1796 tests performed); while the vacuum team also replaced or consolidated around 150 turbomolecular pumps acting on the cryogenic insulation vacuum. In total, 2.4 km of non-evaporable-getter (NEG)-coated beampipes were also opened to the air at room temperature – an exhaustive programme of work spanning mechanical repair and upgrade (across 120 weeks), bakeout (spread across 90 weeks) and NEG activation (over 45 weeks). “The vacuum level in these beampipes is now in the required range, with most of the pressure readings below 10^–10 mbar,” explains Chiggiato.  

Close control

Another LS2 priority for Chiggiato and colleagues involved upgrades to CERN’s vacuum control infrastructure, with the emphasis on reducing single points of failure and the removal of confusing architectures (i.e. systems with no clear separation of function amongst the different programmable logic controllers). “For the first time,” adds Chiggiato, “mobile vacuum equipment was controlled and monitored by wireless technologies – a promising communication choice for distributed systems and areas of the accelerator complex requiring limited stay.” 

Elsewhere, in view of the higher LHC luminosity (and consequent increased radioactivity) following LS2 works, the vacuum group developed and installed advanced radiation-tolerant electronics to control 100 vacuum gauges and valves in the LHC dispersion suppressors. This roll-out represents the first step of a longer-term campaign that will be scaled during the next Long Shutdown (LS3 is scheduled for 2025–2027), including the production of 1000 similar electronic cards for vacuum monitoring. “In parallel,” says Chiggiato, “we have renewed the vacuum control software – introducing resilient, easily scalable and self-healing web services technologies and frameworks used by some of the biggest names in industry.” 

Success breeds success

In the LHC experimental area, meanwhile, the disassembly of the vacuum chambers at the beginning of LS2 required 93 interventions and 550 person-hours of work in the equipment caverns. Reinstallation has progressed well in the four core LHC experiments, with the most impressive refit of vacuum hardware in the CMS and LHCb detectors. 

For the former, the vacuum team installed a new central beryllium chamber (internal diameter 43.4 mm, 7.3 m long), while 12 new aluminium chambers were manufactured, surface-finished and NEG-coated at CERN. Their production comprised eight separate quality checks, from surface treatment to performance assessment of the NEG coating. “The mechanical installation – including alignments, pump-down and leak detection – lasted two months,” explains Chiggiato, “while the bake-out equipment installation, bake-out process, post-bake-out tests and venting with ultrapure neon required another month.” 

Thankfully, creative problem-solving is part of the vacuum team’s DNA

In LHCb, the team contributed to the new version of the Vertex Locator (VELO) sub-detector. The VELO’s job is to pick out B mesons from the multitude of other particles produced – a tricky task as their short lives will be spent close to the beam. To find them, the VELO’s RF box – a delicate piece of equipment filled with silicon detectors, electronics and cooling circuits – must be positioned perilously close to the point where protons collide. In this way, the sub-detector faces the beam at a distance of just 5 mm, with an aluminium window thinned down to 150 μm by chemical etching prior to the deposition of a NEG coating. 

As the VELO encloses the RF box, and both volumes are under separate vacuum, the pumpdown is a critical operation because pressure differences across the thin window must be lower than 10 mbar to ensure mechanical integrity. “This work is now complete,” says Chiggiato, “and vacuum control of the VELO is in the hands of the CERN vacuum team after a successful handover from specialists at Nikhef [the Dutch National Institute for Subatomic Physics].” 

Wrapping up a three-year effort, the vacuum team’s last planned activity in LS2 involves the bake-out of the ATLAS and CMS beampipe in early 2022. “There was no shortage of technical blockers and potential show-stoppers during our LS2 work programme,” Chiggiato concludes. “Thankfully, creative problem-solving is part of the vacuum team’s DNA, as is the rigorous application of vacuum best practice and domain knowledge accumulated over decades of activity. Ours is a collective mindset, moreover, driven by a humble approach to such complex technological installations, where every single detail can have important consequences.”

A detailed report on the CERN vacuum team’s LS2 work programme – including the operational and technical challenges along the way – will follow in the March/April 2022 issue of CERN Courier magazine.

The post Detail and diligence ensure LS2 progress appeared first on CERN Courier.

Sweden’s MAX IV synchrotron radiation facility is among an elite cadre of advanced X-ray sources, shedding light on the structure and behaviour of matter at the atomic and molecular level across a range of fundamental and applied disciplines – from clean-energy technologies to pharma and healthcare, from structural biology and nanotech to food science and cultural heritage. 

In terms of core building blocks, this fourth-generation light source – which was inaugurated in 2016 – consists of a linear electron accelerator plus 1.5 and 3 GeV electron storage rings (with the two rings optimised for the production of soft and hard X rays, respectively). As well as delivering beam to a short-pulse facility, the linac serves as a full-energy injector to the two storage rings which, in turn, provide photons that are extracted for user experiments across 14 specialist beamlines.

Underpinning all of this is a ground-breaking implementation of ultrahigh-vacuum (UHV) technologies within MAX IV’s 3 GeV electron storage ring – the first synchrotron storage ring in which the inner surface of almost all the vacuum chambers along its circumference are coated with non-evaporable-getter (NEG) thin film for distributed pumping and low dynamic outgassing. Here, Marek Grabski, MAX IV vacuum section leader, gives CERN Courier the insider take on a unique vacuum installation and its subsequent operational validation. 

What are the main design challenges associated with the 3 GeV storage-ring vacuum system?

We were up against a number of technical constraints that necessitated an innovative approach to vacuum design. The vacuum chambers, for example, are encapsulated within the storage ring’s compact magnet blocks with bore apertures of 25 mm diameter (see “The MAX IV 3 GeV storage ring: unique technologies, unprecedented performance”). What’s more, there are requirements for long beam lifetime, space limitations imposed by the magnet design, the need for heat dissipation from incoming synchrotron radiation, as well as minimal beam-coupling impedance. 

The answer, it turned out, is a baseline design concept that exploits NEG thin-film coatings, a technology originally pioneered by CERN that combines distributed pumping of active residual gas species with low photon-stimulated desorption. The NEG coating was applied by magnetron sputtering to almost all the inner surfaces (98% lengthwise) of the vacuum chambers along the electron beam path. As a consequence, there are only three lumped ion pumps fitted on each standard “achromat” (20 achromats in all, with a single acromat measuring 26.4 m end-to-end). That’s far fewer than typically seen in other advanced synchrotron light sources. 

The MAX IV 3 GeV storage ring: unique technologies, unprecedented performance

Among the must-have user requirements for the 3 GeV storage ring was the specified design goal of reaching ultralow electron-beam emittance (and ultrahigh brightness) within a relatively small circumference (528 m). As such, the bare lattice natural emittance for the 3 GeV ring is 328 pm rad – more than an order of magnitude lower than typically achieved by previous third-generation storage rings in the same energy range.

Even though the fundamental concepts for realising ultralow emittance had been laid out in the early 1990s, many in the synchrotron community remained sceptical that the innovative technical solutions proposed for MAX IV would work. Despite the naysayers, on 25 August 2015 the first electron beam circulated in the 3 GeV storage ring and, over time, all design parameters were realised: the fourth generation of storage-ring-based light sources was born. 

Stringent beam parameters 

The MAX IV 3 GeV storage ring represents the first deployment of a so-called multibend achromat magnet lattice in an accelerator of this type, with the large number of bending magnets central to ensuring ultralow horizontal beam emittance. In all, there are seven bending magnets per achromat (and 20 achromats making up the complete storage ring). 

Not surprisingly, miniaturisation is a priority in order to accommodate the 140 magnet blocks – each consisting of a dipole magnet and other magnet types (quadrupoles, sextupoles, octupoles and correctors) – into the ring circumference. This was achieved by CNC machining the bending magnets from a single piece of solid steel (with high tolerances) and combining them with other magnet types into a single integrated block. All magnets within one block are mechanically referenced, with only the block as a whole aligned on a concrete girder.

Vacuum innovation

Meanwhile, the vacuum system design for the 3 GeV storage ring also required plenty of innovative thinking, key to which was the close collaboration between MAX IV and the vacuum team at the ALBA Synchrotron in Barcelona. For starters, the storage-ring vacuum vessels are made from extruded, oxygen-free, silver-bearing copper tubes (22 mm inner diameter, 1 mm wall thickness). 

Copper’s superior electrical and thermal conductivities are crucial when it comes to heat dissipation and electron beam impedance. The majority of the chamber walls act as heat absorbers, directly intercepting synchrotron radiation coming from the bending magnets. The resulting heat is dissipated by cooling water flowing in channels welded on the outer side of the vacuum chambers. Copper also absorbs unwanted radiation better than aluminium, offering enhanced protection for key hardware and instrumentation in the tunnel. 

The use of crotch absorbers for extraction of the photon beam is limited to one unit per achromat, while the section where synchrotron radiation is extracted to the beamlines is the only place where the vacuum vessels incorporate an antechamber. Herein the system design is particularly challenging, with the need for additional cooling blocks to be introduced on the vacuum chambers with the highest heat loads. 

Other important components of the vacuum system are the beam position monitors (BPMs), which are needed to keep the synchrotron beam on an optimised orbit. There are 10 BPMs in each of the 20 achromats, all of them decoupled thermally and mechanically from the vacuum chambers through RF-shielded bellows that also allow longitudinal expansion and small transversal movement of the chambers.

Ultimately, the space constraints imposed by the closed magnet block design – as well as the aggregate number of blocks along the ring circumference – was a big factor in the decision to implement a NEG-based pumping solution for MAX IV’s 3 GeV storage ring. It’s simply not possible to incorporate sufficient lumped ion pumps to keep the pressure inside the accelerator at the required level (below 1 × 10^–9 mbar) to achieve the desired beam lifetime while minimising residual gas–beam interactions. 

Operationally, it’s worth noting that a purified neon venting scheme (originally developed at CERN) has emerged as the best-practice solution for vacuum interventions and replacement or upgrade of vacuum chambers and components. As evidenced on two occasions so far (in 2018 and 2020), the benefits include significantly reduced downtime and risk management when splitting magnets and reactivating the NEG coating. 

How important was collaboration with CERN’s vacuum group on the NEG coatings?

Put simply, the large-scale deployment of NEG coatings as the core vacuum technology for the 3 GeV storage ring would not have been possible without the collaboration and support of CERN’s vacuum, surfaces and coatings (VSC) group. Working together, our main objective was to ensure that all the substrates used for chamber manufacturing, as well as the compact geometry of the 3 GeV storage-ring vacuum vessels, were compatible with the NEG coating process (in terms of coating adhesion, thickness, composition and activation behaviour). Key to success was the deep domain knowledge and proactive technical support of the VSC group, as well as access to CERN’s specialist facilities, including the mechanical workshop, vacuum laboratory and surface treatment plant. 

What did the manufacturing model look like for this vacuum system? 

Because of the technology and knowledge transfer from CERN to industry, it was possible for the majority of the vacuum chambers to be manufactured, cleaned, NEG-coated and tested by a single commercial supplier – in this case, FMB Feinwerk- und Messtechnik in Berlin, Germany. Lengthwise, 70% of the chambers were NEG-coated by the same vendor. Naturally, the manufacturing of all chambers had to be compatible with the NEG coating, which meant careful selection and verification of materials, joining methods (brazing) and handling. Equally important, the raw materials needed to undergo surface treatment compatible with the coating, with the final surface cleaning certified by CERN to ensure good film adhesion under all operating conditions – a potential bottleneck that was navigated thanks to excellent collaboration between the three parties involved. 

To spread the load, and to relieve the pressure on our commercial supplier ahead of system installation (which commenced in late 2014), it’s worth noting that most geometrically complicated chambers (including vacuum vessels with a 5 mm vertical aperture antechamber) were NEG-coated at CERN. Further NEG coating support was provided through a parallel collaboration with the European Synchrotron Radiation Facility (ESRF) in Grenoble. 

How did you handle the installation phase? 

This was a busy – and at times stressful – phase of the project, not least because all the vacuum chambers were being delivered “just-in-time” for final assembly in situ. This approach was possible thanks to exhaustive testing and qualification of all vacuum components prior to shipping from the commercial vendor, while extensive dialogue with the MAX IV team helped to resolve any issues arising before the vacuum components left the factory. 

Owing to the tight schedule for installation – just eight months – we initiated a collaboration with the Budker Institute of Nuclear Physics (BINP) in Russia to provide additional support. For the duration of the installation phase, we had two teams of specialists from BINP working alongside (and coordinated by) the MAX IV vacuum team. All vacuum-related processes – including assembly, testing, baking and NEG activation of each achromat (at 180 °C) – took place inside the accelerator tunnel directly above the opened lower magnet blocks of MAX IV’s multibend achromat (MBA) lattice. Our installation approach, though unconventional, yielded many advantages – not least, a reduction in the risks related to transportation of assembled vacuum sectors as well as reduced alignment issues. 

Presumably not everything went to plan through installation and acceptance?

One of the issues we encountered during the initial installation phase was a localised peeling of the NEG coating on the RF-shielded bellows assembly of several vacuum vessels. This was addressed as a matter of priority – NEG film fragments falling into the beam path is a show-stopper – and all the effected modules were replaced by the vendor in double-quick time. More broadly, the experience of the BINP staff meant difficulties with the geometry of a few chambers could also be resolved on the spot, while the just-in-time delivery of all the main vacuum components worked well, such that the installation was completed successfully and on time. After completion of several achromats, we installed straight sections in between while the RF cavities were integrated and conditioned in situ. 

How has the vacuum system performed from the commissioning phase and into regular operation? 

Bear in mind that MAX IV was the first synchrotron light source to apply NEG technology on such a scale. We were breaking new ground at the time, so there were credible concerns regarding the conditioning and long-term reliability of the NEG vacuum system – and, of course, possible effects on machine operation and performance. From commissioning into regular operations, however, it’s clear that the NEG pumping system is reliable, robust and efficient in delivering low dynamic pressure in the UHV regime.

Initial concerns around potential saturation of the NEG coating in the early stages of commissioning (when pressures are high) proved to be unfounded, while the same is true for the risk associated with peeling of the coating (and potential impacts on beam lifetime). We did address a few issues with hot-spots on the vacuum chambers during system conditioning, though again the overall impacts on machine performance were minimal. 

To sum up: the design current of 500 mA was successfully injected and stored in November 2018, proving that the vacuum system can handle the intense synchrotron radiation. After more than six years of operation, and 5000 Ah of accumulated beam dose, it is clear the vacuum system is reliable and provides sustained UHV conditions for the circulating beam – a performance, moreover, that matches or even exceeds that of conventional vacuum systems used in other storage rings.

What are the main lessons your team learned along the way through design, installation, commissioning and operation of the 3 GeV storage-ring vacuum system?

The unique parameters of the 3 GeV storage ring were delivered according to specification and per our anticipated timeline at the end of 2015. Successful project delivery was only possible by building on the collective experience and know-how of staff at MAX-lab (MAX IV’s predecessor) constructing and operating accelerators since the 1970s – and especially the lab’s “explorer mindset” for the early-adoption of new ideas and enabling technologies. Equally important, the commitment and team spirit of our technical staff, reinforced by our collaborations with colleagues at ALBA, CERN, ESRF and BINP, were fundamental to the realisation of a relatively simple, efficient and compact vacuum solution.

Operationally, it’s worth adding that there are many dependencies between the chosen enabling technologies in a project as complex as the MAX IV 3 GeV storage ring. As such, it was essential for us to take a holistic view of the vacuum system from the start, with the choice of a NEG pumping solution enforcing constraints across many aspects of the design – for example, chamber geometry, substrate type, surface treatment and the need for bellows. The earlier such knowledge is gathered within the laboratory, the more it pays off during construction and operation. Suffice to say, the design and technology solutions employed by MAX IV have opened the door for other advanced light sources to navigate and build on our experience.

The post MAX IV: partnership is the key appeared first on CERN Courier.

By 2040, the annual global incidence of cancer is expected to rise by more than 42% from 19.3 million to 27.5 million cases, corresponding to approximately 16.3 million deaths. Shockingly, some 70% of these new cases will be in low- and middle-income countries (LMICs), which lack the healthcare programmes required to effectively manage their cancer burden. While it is estimated that about half of all cancer patients would benefit from radiotherapy (RT) for treatment, there is a significant shortage of RT machines outside high-income countries.

More than 10,000 electron linear accelerators (linacs) are currently used worldwide to treat patients with cancer. But only 10% of patients in low-income and 40% in middle-income countries who need RT have access to it. Patients face long waiting times, are forced to travel to neighbouring regions or face insurmountable expenditure to access treatment. In Africa alone, 27 out of 55 countries have no linac-based RT facilities. In those that do, the ratio of the number of machines to people ranges from one machine to 423,000 people in Mauritius, one machine to almost five million people in Kenya and one machine to more than 100 million people in Ethiopia (see “Out of balance” image). In high-income countries such as the US, Switzerland, Canada and the UK, by contrast, the ratio is one RT machine to 85,000, 102,000, 127,000 and 187,000 people, respectively. To draw another stark comparison, Africa has approximately 380 linacs for a population of 1.2 billion while the US has almost 4000 linacs for a population of 331 million.

Unique challenges

It is estimated that to meet the demand for RT in LMICs over the next two to three decades, the current projected need of 5000 RT machines is likely to become more than 12,000. To put these figures into perspective, Varian, the market leader in RT machines, has a current worldwide installation base of 8496 linacs. While many LMICs provide RT using cobalt-60 machines, linacs offer better dose-delivery parameters and better treatment without the environmental and potential terrorism risks associated with cobalt-60 sources. However, since linacs are more complex and labour-intensive to operate and maintain, their current costs are significantly higher than cobalt-60 machines, both in terms of initial capital costs and annual service contracts. These differences pose unique challenges in LMICs, where macro- and micro-economic conditions can influence the ability of these countries to provide linac-based RT. 

In November 2016 CERN hosted a first-of-its-kind workshop, sponsored by the International Cancer Expert Corps (ICEC), to discuss the design characteristics of RT linacs (see “Linac essentials” image) for the challenging environments of LMICs. Leading experts were invited from international organisations, government agencies, research institutes, universities and hospitals, and companies that produce equipment for conventional X-ray and particle therapy. The following October, CERN hosted a second workshop titled “Innovative, robust and affordable medical linear accelerators for challenging environments”, co-sponsored by the ICEC and the UK’s Science and Technology Facilities Council, STFC. Additional workshops have taken place in March 2018, hosted by STFC in collaboration with CERN and the ICEC, and in March 2019, hosted by STFC in Gaborone, Botswana (see “Healthy vision” image). These and other efforts have identified substantial opportunities for scientific and technical advancements in the design of the linac and the overall RT system for use in LMICs. In 2019, the ICEC, CERN, STFC and Lancaster University entered into a formal collaboration agreement to continue concerted efforts to develop this RT system. 

The idea of novel medical linacs is an excellent example of the impact of fundamental research on wider society

In June 2020, STFC funded a project called ITAR (Innovative Technologies towards building Affordable and equitable global Radiotherapy capacity) in partnership with the ICEC, CERN, Lancaster University, the University of Oxford and Swansea University. ITAR’s first phase was aimed at defining the persistent shortfalls in basic infrastructure, equipment and specialist workforce that remain barriers to effective RT delivery in LMICs. Clearly, a linac suitable for these conditions needs to be low-cost, robust and easy to maintain. Before specifying a detailed design, however, it was first essential to assess the challenges and difficulties RT facilities face in LMICs and in other demanding environments. Published in June 2021, an expansive study of RT facilities in 28 African countries was carried out and compared to western hospitals by the ITAR team to quantitatively and qualitatively assess and compare variables in several domains (see “Downtime” figure). The survey builds on a related 2018 study on the availability of RT services and barriers to providing such services in Botswana and Nigeria, which looked at the equipment maintenance logs of linacs in those countries and selected facilities in the UK.

Surveying the field

The absence of detailed data regarding linac downtime and failure modes makes it difficult to determine the exact impact of the LMIC environment on the performance of current technology. The ongoing ITAR design development and prototyping process identified a need for more information on equipment failures, maintenance and service shortcomings, personnel, training and country-specific healthcare challenges from a much larger representation of LMICs. A further-reaching ITAR survey obtained relevant information for defining design parameters and technological choices based on issues raised at the workshops. They include well-recognised factors such as ease and reliability of operation, machine self-diagnostics and a prominent display of impending or actual faults, ease of maintenance and repair, insensitivity to power interruptions, low power requirement and the consequent reduced heat production.

Based on the information from its surveys, ITAR produced a detailed specification and conceptual design for an RT linac that requires less maintenance, has fewer failures and offers fast repair. Over the next three years, under the umbrella of a larger project called STELLA (Smart Technologies to Extend Lives with Linear Accelerators) launched in June 2020, the project will progress to a prototype development phase at STFC’s Daresbury Laboratory. 

The design of the electron gun has been optimised to increase beam-capture. This has the dual advantage of reducing both the peak current required from the gun to deliver the requisite dose and “back bombardment”. It also allows for simpler replacement of the electron gun’s cathode by trained personnel (current designs require replacement of the full electron gun or even the full linac). Electron-beam capture is limited in medical linacs as the pulses from the electron gun are much longer in duration than the radiofrequency (RF) period, meaning electrons are injected at all RF phases. Some phases cause the bunch to be accelerated while others result in electrons being reflected back to the cathode. In typical linacs, less than 50% of electrons reach the target and many electrons reach the target with lower energies. In high-energy accelerators velocity bunching can be used to compress the bunch, however the space is limited in medical linacs and the energy gain per cell is often well in excess of the beam energy. To allow velocity bunching in a medical linac, the first cell needs to operate at a low gradient – such that less space is required to bunch as the average beam velocity is much lower and the deceleration is less than the beam energy. By adjusting the length of the first and second cells, the decelerated electrons can re-accelerate on the next RF cycle and synchronise with the accelerated electrons, capturing nearly all the electrons and transporting them to the target without a low-energy tail. This is achieved using techniques originally developed for the optimisation of klystrons as part of the Compact Linear Collider project at CERN. By adjusting cell-to-cell coupling, it is possible to make all the other cells at a higher gradient similar to a standard medical linac such that the total linac length remains the same (see “Strong coupling” figure).

The electrical power supply in LMICs can often be variable and protection equipment to isolate harmonics between pieces of equipment is not always installed, hence it is critical to consider this when designing the electrical system for RT machines. This in itself is relatively straightforward but is not normally considered as part of a RT machine design.

The failure of multi-leaf collimators (MLCs), which alter the intensity of the radiation so that it conforms to the tumour volume via several individually actuated leaves, is a major linac downtime issue. Designing MLCs that are less prone to failure will play a key role in RT in LMICs, with studies ongoing into ways to simplify the design without compromising on treatment quality.

Building a workforce

Making it simpler to diagnose and repair faults on linacs is another key area that needs improvement. Given the limited technical staff training in some LMICs, when a machine fails it can be challenging for local staff to make repairs. In addition, components that are degrading can be missed by staff, leading to loss of valuable time to order spares. An important component of the STELLA project, led by ICEC, is to enhance existing and establish new twinning programmes that provide mentoring and training to healthcare professionals in LMICs to build workforce capacity and capability in those regions.

The idea to address the need for a novel medical linac for challenging environments was first presented by Norman Coleman, senior scientific advisor to the ICEC, at the 2014 ICTR-PHE meeting in Geneva. This led to the creation of the STELLA project, led by Coleman and ICEC colleagues Nina Wendling and David Pistenmaa, which is now using technology originally developed for high-energy physics to bring this idea closer to reality – an excellent example of the impact of fundamental research on wider society. 

The next steps are to construct a full linac prototype to verify the higher capture, as well as to improve the ease of maintaining and repairing the machine. Then we need to have the RT machine manufactured for use in LMICs, which will require many practical and commercial challenges to be overcome. The aim of project STELLA to make RT truly accessible to all cancer patients brings to mind a quote from the famous Nigerian novelist Chinua Achebe: “While we do our good works let us not forget that the real solution lies in a world in which charity will have become unnecessary.” 

The post Linacs to narrow radiotherapy gap appeared first on CERN Courier.

Just over 60 years ago, physicists and engineers at CERN were hard at work trying to tune the world’s first proton synchrotron, the PS. It was the first synchrotron of its kind, employing the strong-focusing principle to produce higher-energy beams within a smaller aperture and with a lower construction cost compared to, for example, the CERN synchrocyclotron. Little could physicists in 1959 imagine the maze of technical galleries and tunnels stemming out of the PS ring not many years later.

The first significant expansion to CERN’s accelerator complex was prompted by the 1962 discovery of the muon neutrino at the competing Alternating Gradient Synchrotron at Brookhaven National Laboratory in the US. Soon afterwards, CERN embarked on an ambitious programme starting with a new east experimental area, the PS booster and the first hadron collider – the Intersecting Storage Rings (ISR). A major challenge during this expansion was transferring the beam to targets, experiments and the ISR, which required that CERN build transfer lines that could handle different particles, different extraction energy levels and various duty cycles (see “In service” figure).

Transfer lines transport particle beams from one machine to another using powerful magnets. Once fully accelerated, a beam is given an ultra-fast “kick” off its trajectory by a kicker magnet and then guided away from the ring by one or more septum magnets. A series of focusing and defocusing quadrupole magnets contain the beams in the vacuum pipe while bending magnets direct them to their new destination (a target or a subsequent accelerator ring).

Making the connection

The first transfer lines linking two different CERN accelerators were TT1 and TT2, which were originally built for the ISR. The need to handle different particle energies and even different particle charges required continuous adjustment of the magnetic field at every extraction, typically once per second in the PS. One of the early challenges faced was a memory effect in the steel yokes of the magnets: alternating among different field values leaves a remnant field that changes the field density depending on the order of cycles played out before. Initially, complex solutions with secondary field-resetting coils were used. Later, magnetic reset was achieved by applying a predefined field excitation that brings the magnet to a reproducible state prior to the next physics cycle.

Solving the magnetic hysteresis problem was not the only hurdle that engineers faced. Handling rapid injections and extractions through the magnets was also a major challenge for the electronics of the time. The very first powering concept used machine/generator setups with adjustable speeds to modulate the electric current and consequently the field density in the transfer-line magnets. Each transfer line would have its own noisy generation plant that required a control room with specialised personnel (see “Early days” images). Modifying the mission-profile of a magnet to test new physics operations was a heavy and tedious operation.

Towards the end of 1960s, electrical motors in the west PS hall were replaced by the first semiconductor-operated thyristor rectifiers, which transformed the 50 Hz alternating grid voltage to a precisely regulated (to nearly 100 parts per million) current in the beamline magnets. They also occupied a fraction of the space, had lower power losses and were able to operate unsupervised. All of a sudden, transporting different particles with variable energies became possible at the touch of a knob. The timing could not have been better, as CERN prepared itself for the Super Proton Synchrotron (SPS) era, which would see yet more transfer lines added to its accelerator complex. 

By the early 1980s the ISR had completed its mission, and the TT1 transfer line was decommissioned together with the storage rings. However, the phenomenal versatility of TT2 has allowed it to continue to extract particles for experiments. Today, virtually all user beams, except those for the East Area and ISOLDE, pass through the 300 m-long line. It delivers low-energy 3 GeV beams to “Dump 2” for machine development, 14 GeV beams to the SPS for various experiments in the North Area, 20 GeV beams towards the n_ToF facility, 26 GeV beams to the Antiproton Decelerator, and to the SPS – where protons are accelerated to 450 GeV before being injected into the LHC. While beams traverse TT2 in just over a microsecond, other beamlines, such as those in the East Area, spill particles out of the PS continuously for 450 ms towards the CLOUD experiment and other facilities – a process known as slow extraction.

Energy economy 

Transfer lines are heavy users of electrical power, since typically their magnets are powered for long periods compared to the time it takes a beam to pass. During their last year of operation in 2017, for example, the East Area transfer lines accounted for 12% of all energy consumption by CERN’s PS/PSB injector complex. The reason for this inefficiency was the non-stop powering of the few dozen magnets used in each transfer line for the necessary focusing, steering and trajectory-correction functions. This old powering system, combined with a solid-yoke magnet structure, did not permit extraction of the magnetic field energy between beam operations. 

CERN is looking at testing and implementing new systems that lower its environmental impact today and into the far future

For reference, a typical bending magnet absorbs the same energy as a high-performance car accelerating from 0 to 100 km/h, and must do so in a period of 0.5 s every 1.2 s for beams from the PS. To supply and recover all this energy between successive beam operations, powerful converters are required along with laminated steel magnet yokes, all of which became possible with the recent East Area renovation project. 

Energy economy was the primary motivation for CERN to adopt the “Sirius” family of regenerative power converters for TT2 and, subsequently, the East Area and Booster transfer lines. While transfer lines typically absorb and return all the magnetic field energy from and to the power grid, the new Sirius power converter allows a more energy-efficient approach by recovering the magnetic field energy locally into electrolytic capacitors for re-use in the next physics cycle. Electrolytic capacitors are the only energy-storage technology that can withstand the approximately 200 million beam transports that a Sirius converter is expected to deliver during its lifetime, and the system employs between 15 and 420 such wine-bottle-sized units according to the magnet size and beam energy to be supplied (see “Transformational” image).

Sirius is also equipped with a front-end unit that can control the energy flow from the grid to match what is required to compensate the thermal losses in the system. By estimating in real time how much of the total energy can be recycled, Sirius has enabled the newly renovated East Area to be powered using only two large-distribution transformers rather than the seven transformers used in the past for the old 1960s thyristor rectifiers. To control the energy flow in the magnets, Sirius uses powerful silicon-based semiconductors that switch on and off 13,000 times per second. By adjusting the “on” time of the switches the average current in and out of the energy-storing units can be controlled with precision, while the high switching frequency allows rapid corrections of the generated voltage and current across the magnet.

The Sirius converters entered operation gradually from September 2020, and at present a total of 500 million magnetic cycles have been completed. Recent measurements made on the first circuits commissioned in the East Area demonstrated an energy consumption 95% lower than compared to the original 1960s figures. But above all, the primary role of Sirius is to provide current and hence magnetic field in transfer-line magnets to a precision of 10 parts per million, which enables excellent reproducibility for the beams coming down the lines. The most recent measurements demonstrated a stability better than 10 ppm during a 24-hour interval.

Unusual engineering model 

CERN employs a rather unusual engineering model compared to those in industry. For Sirius, a team of experts and technicians from the electrical power converters group designed, prototyped and validated the power-converter design before issuing international tenders to procure the subsystems, assembly and testing. Engineers therefore have the opportunity to work with their counterparts in member-state industries, often helping them develop new manufacturing methods and skills. Sirius, for example, helped a magnetics-component manufacturer in Germany achieve a record precision in their manufacturing process and to improve their certification procedures for medium-power reactors. Another key partner acquired new knowledge in the manufacturing and testing of inoxidised water-cooling circuits, enabling the firm to expand its project portfolio. 

Thanks to the CERN procurement process, Sirius components are built by a multitude of suppliers across Europe. For some, it was their first time working with CERN. For example, the converter-assembly contract was the first major (CHF 12 million) contract won by Romanian industry after the country’s accession to CERN five years ago. Other significant contributions were made by German, Dutch, French, UK, Danish and Swedish industries. Recent work by the CERN knowledge transfer group resulted in a contract with a Spanish firm that licensed the Sirius design for production for other laboratories, with the profits invested in R&D for future converter families.

Energy recycling tends to yield more impressive energy savings in fast-cycling accelerators and transfer lines, such as those in the PS. However, CERN is planning to deploy similar technologies in other experimental facilities such as the North Area that will undergo a major makeover in the following years. The codename for this new converter project is Polaris – a scalable converter family that can coast through the long extraction plateaus used in the SPS (see “Physics cycles” figure). The primary goal of the renovation, beyond better energy efficiency, is to restore the reliability and provide a 10-fold improvement in the precision of the magnetic field regulation.

Development efforts in the power-converters group do not stop here. The electrification of transportation and the net-zero carbon emission targets of many governments are also driving innovation in power electronics, which CERN might take advantage of. For example, wide bandgap semiconductors exhibit higher reverse-blocking capabilities and faster transitions that could allow switching at a rate of more than 40,000 Hz and therefore help to reduce size, losses and eliminate the audible noise emitted by power conversion altogether. 

Another massive opportunity concerns energy storage, with CERN looking closely at the technologies driven by the battery mega-factories that are being built around the world. As part of our mission to provide the next generation of sustainable scientific facilities, as outlined in CERN’s recently released second environment report, we are looking at testing and implementing new systems to lower our environmental impact today and into the far future. 

The post Powering for a sustainable future appeared first on CERN Courier.

Former CERN Director-General (DG) Chris Llewellyn Smith swiftly did away with notions that the ISR was built without a physics goal. Viki Weisskopf (DG at the time) was well aware of the quark model, he said, and urged that the ISR be built to discover quarks. “The basic structure of high-energy collisions was discovered at the ISR, but you don’t get credit for it because it is so obvious now,” said Llewellyn Smith. Summarising the ISR physics programme, Ugo Amaldi, former DELPHI spokesperson and a pioneer of accelerators for hadron therapy, listed the observation of charmed-hadron production in hadronic interactions, studies of the Drell–Yan process, and measurements of the proton structure function as ISR highlights. He also recalled the frustration at CERN in late 1974 when the J/ψ meson was discovered at Brookhaven and SLAC, remarking that history would have changed dramatically had the ISR detectors also enabled coverage at high transverse momentum.

A beautiful machine

Amaldi sketched the ISR’s story in three chapters: a brilliant start followed by a somewhat difficult time, then a very active and interesting programme. Former CERN director for accelerators and technology Steve Myers offered a first-hand account, packed with original hand-drawn plots, of the battles faced and the huge amount learned in getting the first hadron collider up and running. “The ISR was a beautiful machine for accelerator physics, but sadly is forgotten in particle physics,” he said. “One of the reasons is that we didn’t have beam diagnostics, on account of the beam being a coasting beam rather than a bunched beam, which made it really hard to control things during physics operation.” Stochastic cooling, a “huge surprise”, was the ISR’s most important legacy, he said, paving the way for the SppS and beyond.

Former LHC project director Lyn Evans took the baton, describing how the confluence of electroweak theory, the SPS as collider and stochastic cooling led to rapid progress. It started with the Initial Cooling Experiment in 1977–1978, then the Antiproton Accumulator. It would take about 20 hours to produce a bunch dense enough for injection into the SppS , recalled Evans, and several other tricks to battle past the “26 GeV transition, where lots of horrible things” happened. At 04:15 on 10 July 1981, with just him and Carlo Rubbia in the control room, first collisions at 270 GeV at the SppS were declared.

Poignantly, Evans ended his presentation “The SPS and LHC machines” there. “The LHC speaks for itself really,” he said. “It is a fantastic machine. The road to it has been a long and very bumpy one. It took 18 years before the approval of the LHC and the discovery of the Higgs. But we got there in the end.”

Discovery machines

The parallel world of hadron-collider experiments was brought to life by Felicitas Pauss, former CERN head of international relations, who recounted her time as a member of the UA1 collaboration at the SppS during the thrilling period of the W and Z discoveries. Jumping to the present day, early-career researchers from the ALICE, ATLAS, CMS and LHCb collaborations brought participants up to date with the progress at the LHC in testing the Standard Model and the rich physics prospects at Run 3 and the HL-LHC.

Few presentations at the symposium did not mention Carlo Rubbia, who instigated the conversion of the SPS into a hadron collider and was the prime mover of the LHC, particularly, noted Evans, during the period when the US Superconducting Super Collider was under construction. His opening talk presented a commanding overview of colliders, their many associated Nobel prizes and their applications in wider society.

During a brief Q&A at the end of his talk, Rubbia reiterated his support for a muon collider operating as a Higgs factory in the LHC tunnel: “The amount of construction is small, the resources are reasonable, and in my view it is the next thing we should do, as quickly as possible, in order to make sure that the Higgs is really what we think it is.”

It seems in hindsight that the LHC was inevitable, but it was anything but

Christopher Llewellyn Smith

In a lively and candid presentation about how the LHC got approved, Llewellyn Smith also addressed the question of the next collider, noting it will require the unanimous support of the global particle-physics community, a “reasonable” budget envelope and public support. “It seems in hindsight that the LHC was inevitable, but it was anything but,” he said. “I think going to the highest energy is the right way forward for CERN, but no government is going to fund a mega project to reduce error bars – we need to define the physics case.”

Following a whirlwind “view from the US”, in which Young-Kee Kim of the University of Chicago described the Tevatron and RHIC programmes and collated congratulatory messages from the US Department of Energy and others, CERN DG Fabiola Gianotti rounded off proceedings with a look at the future of the LHC and beyond. She updated participants on the significant upgrade work taking place for the HL-LHC and on the status of the Future Circular Collider feasibility study, a high-priority recommendation of the 2020 update of the European strategy for particle physics which is due to be completed in 2025. “The extraordinary success of the LHC is the result of the vision, creativity and perseverance of the worldwide high-energy physics community and more than 30 years of hard work,” the DG stated. “Such a success demonstrates the strength of the community and it’s a necessary milestone for future, even more ambitious, projects.”

Videos from the one-off symposium, capturing the rich interactions between the people who made hadron colliders a reality, are available here.

The post Hadron colliders in perspective appeared first on CERN Courier.

Future scientific breakthroughs in high-energy physics will require unprecedented levels of international engagement, building on the successful model of the Large Hadron Collider at CERN. Joe Lykken, Fermilab deputy director for research, will describe how Fermilab is moving forward rapidly with CERN and other international partners to realise this vision.

The questions under scrutiny range from the nature of the Higgs field to the question of whether neutrinos play a role in the matter-antimatter asymmetry observed in the universe. PIP-II, an upgrade to the Fermilab accelerator complex that includes a leading-edge superconducting linear accelerator, is already under construction, with major “in-kind” contributions and expertise from partners in India, Italy, the UK, France and Poland. PIP-II will enable the world’s most intense beam of neutrinos for the Deep Underground Neutrino Experiment (DUNE), which will deploy 70,000 tonnes of liquid argon detectors in a deep underground site 1300 km from Fermilab. DUNE was formulated as an international project from the start, and now includes more than a thousand collaborators from 30 countries. Two large prototype detectors for DUNE have been successfully constructed and tested at the CERN Neutrino Platform. DUNE will have remarkable capabilities to determine how the properties of neutrinos have shaped our universe. At the same time, Fermilab has been developing and building next-generation superconducting magnets that will be deployed in the HL-LHC accelerator at CERN, and is the US lead for ambitious upgrades to the CMS experiment for the HL-LHC era. These technological capabilities will also make Fermilab an important partner for the proposed Future Circular Collider.

Joseph Lykken is Fermilab’s deputy director of research and leads the Fermilab Quantum Institute. A distinguished scientist at the laboratory, Lykken was a former member of the Theory Department, researching string theory and phenomenology, and is a member of the CMS experiment on the Large Hadron Collider at CERN. He received his PhD from the Massachusetts Institute of Technology and has previously worked for the Santa Cruz Institute for Particle Physics and the University of Chicago. Lykken began his tenure at Fermilab in 1989. He is a former member of the High Energy Physics Advisory Panel, which advises both the Department of Energy and the National Science Foundation, and served on the Particle Physics Project Prioritization Panel, developing a road map for the next 20 years of US particle physics. Lykken is a fellow of the American Physical Society and of the American Association for the Advancement of Science.

The post Fermilab: a future built on international engagement appeared first on CERN Courier.

After a three-year hiatus, protons are once again circulating in the LHC, as physicists make final preparations for the start of Run 3. At the beginning of October, a beam of 450 GeV protons made its way from the Super Proton Synchrotron (SPS) down the TI2 beamline towards Point 2, where it struck a dump block and sprayed secondary particles into the ALICE experiment (see image). Beam was also successfully sent down the TI8 transfer line, which meets the LHC near to where the LHCb experiment is located.

Today, counter-rotating protons were finally injected into the LHC, marking the latest milestone in the reawakening of CERN’s accelerator complex, which closed down at the end of 2018 for Long Shutdown 2 (LS2). Two weeks of beam tests are planned, along with first low-energy collisions in the experiments, before the machine is shut down for a 3-4 month maintenance period. Meanwhile, the experiments are continuing to ready themselves for more luminous Run-3 operations.

Final countdown

Beams have been back at CERN since the spring. After a comprehensive two-year overhaul, the Proton Synchrotron (PS) accelerated its first beams on 4 March and has recently started supplying experiments in the newly refurbished East Area and at the new ELENA ring at the Antimatter Factory. Connecting the brand-new Linac4 to the upgraded PS Booster (which also serves ISOLDE) was a major step in the upgrade programme.  Together, they now provide the PS with a 2 GeV beam, 0.6 GeV up from before, for which the 60-year-old machine had to be fitted out with refurbished magnets, new beam-dump systems, instrumentation, and upgraded RF and cooling systems.

When the LHC comes back online for physics in May 2022, it will not only be more luminous, but it will also operate at higher energies

LS2 saw an even greater overhaul of the SPS, including the addition of a new beam-dump system, a refurbished RF system that now includes the use of solid-state amplifier technology, and a major overhaul of the control system. Combined with the LHC Injectors Upgrade project (the main focus of LS2), the accelerator complex is now primed for more intense beams, in particular for the High-Luminosity LHC (HL-LHC) later this decade.

The first bunch was injected from the PS into the SPS on 12 April, building up to “LHC-like” beams of up to 288 bunches a few weeks later. The SPS delivers beams to all of CERN’s North Area experiments, which include a new facility, NA65, approved in 2019 to investigate fast-neutron production for better understanding of the background in underground neutrino experiments. It also drives the AWAKE experiment, which performs R&D for plasma-wakefield acceleration and entered its second run in July with the goal of demonstrating acceleration gradients of 1 GV/m while preserving the beam quality. The restart of North Area experiments will also see pilot runs for new experiments such as AMBER (the successor of COMPASS) and NA64μ (NA64 running with muon beams).

Brighter and more powerful

When the LHC comes back online for physics in May 2022, it will not only be more luminous (with up to 1.8 × 10¹¹ protons per bunch compared to 1.3–1.4 × 10¹¹ during Run 2), but it will also operate at higher energies. This year, the majority of the LHC’s 1232 dipole magnets were trained to carry 6.8 TeV proton beams, compared to 6.5 TeV before, which involves operating with a current of 11.5 kA (with a margin of 0.1 kA). Following the beam tests this autumn, magnet training for the final two of the machine’s eight sectors will take place during a scheduled maintenance period from 1 November to 21 February. After that, the LHC tunnel and experiment areas will be closed for a two-week-long “cold checkout”, with beam commissioning commencing on 7 March and first stable beams expected during the first week of May.

Meanwhile, the LHC experiments are continuing to ready their detectors for the bumper Run-3 data harvest ahead: at least 160 fb^–1 (as for Run 2) to ATLAS and CMS; 25 fb^–1 to LHCb (compared to 6 fb^–1 in Run 2); and 7.5 nb^–1 of Pb–Pb collisions to ALICE (compared to 1.3 nb^–1 in Run 2). The higher integrated luminosities expected for ALICE and LHCb are largely possible thanks to the ability of their upgraded detectors to handle the Run-3 data rate, with LHCb teams currently working around the clock to ensure their brand-new sub-detectors are in place. New forward-experiments, FASER, FASERν and SND@LHC, which aim to make the first observations of collider neutrinos and open new searches for feebly interacting particles, are also gearing up to take first data when the LHC comes back to life.

“The injector performance reached in 2021 is just the start of squeezing out the potential they have been given during LS2, paving the way for the HL-LHC, but also benefiting the LHC’s performance during Run 3,” says Rende Steerenberg, head of the operations group. “Having beam back in the entire complex and routinely providing the experimental facilities with physics is testimony to the excellent and hard work of many people at CERN.”

The post Protons back with a splash appeared first on CERN Courier.

At the time of the first NuFact in 1999, it wasn’t at all clear that accelerator experiments could address leptonic CP violation in neutrinos. Fits still ignored θ₁₃, which expresses the relatively small coupling between the third neutrino mass eigenstate and the electron, and the size of the solar-oscillation mass splitting, which drives the CP-violating amplitude. Today, leading experiments testify to a precision era of neutrino physics where every parameter in the neutrino mixing matrix must be fitted. TK2, NOvA and MINERvA all reported new analyses and speakers from Fermilab updated the conference on the commissioning of the laboratory’s short-baseline experiments ICARUS, MicroBooNE and SBND, which seek to clarify experimental hints of additional “sterile” neutrinos. After a long journey from CERN to Fermilab, the ICARUS detector, the largest and most downstream of the three liquid-argon detectors in the programme, has been filled with liquid argon, and data taking is now in full swing.

g-2 anomaly

As we strive to pin down the values of the neutrino mixing matrix with a precision approaching that of the CKM matrix, NuFact serves as a key forum for collaborations between theorists and experimentalists. Simon Corrodi (Argonne) showed how the latest results from Fermilab on the g-2 anomaly may suggest new physics in lepton couplings, with potential implications for neutrino couplings and neutrino propagation. Collaboration with accelerator physicists is also important. After the discovery in 2012 that θ₁₃ is nonzero, the focus of experiments with artificial sources of neutrinos turned to the development of multi-MW beams and the need for new facilities. Keith Gollwitzer (Fermilab) kicked off the discussion by summarising Fermilab’s outstanding programme at the intensity frontier, paving the way for DUNE, and Megan Friend (KEK) presented impressive progress in Japan last year. The J-PARC accelerator complex is being upgraded to serve the new T2K near detector, for which the final TPC anode and cathode are now being tested at CERN. The J-PARC luminosity upgrade will also serve the Hyper-Kamiokande experiment, which is due to come online on approximately the same timeline as DUNE. Though the J-PARC neutrino beam will be less intense and by design more monochromatic than that from Fermilab to DUNE, the Hyper-Kamiokande detector will be both closer and larger, promising comparable statistics to DUNE, and addressing the same physics questions at a lower energy.

ENUBET and nuSTORM could operate in parallel with DUNE and Hyper-Kamiokande

A lively round-table discussion featured a dialogue between two of the experiments’ co-spokespersons, Stefan Söldner-Rembold (Manchester) and Francesca Di Lodovico (King’s College London). Both emphasised the complementarity of DUNE and Hyper-Kamiokande, and the need to reduce systematic uncertainties with ad-hoc experiments. J-PARC director Takahashi Kobayashi explored this point in the context of data-driven models and precision experiments such as ENUBET and nuSTORM. Both experiments are in the design phase, and could operate in parallel with DUNE and Hyper-Kamiokande in the latter half of this decade, said Sara Bolognesi (Saclay) and Kenneth Long (Imperial). A satellite workshop focused on potential synergies between these two CERN-based projects and a muon-collider demonstrator, while another workshop explored physics goals and technical challenges for “ESSnuSB” – a proposed neutrino beam at the European Spallation Source in Lund, Sweden. In a plenary talk, Nobel laureate and former CERN Director-General Carlo Rubbia went further still, exploring the possibility of a muon collider at the same facility.

The next NuFact will take place in August 2022 in Salt Lake City, Utah.

The post Artificial-neutrino experiments near precision era  appeared first on CERN Courier.

• While construction work for the $815 million upgrade of Argonne National Laboratory’s Advanced Photon Source (APS) is already well under way, the replacement of the facility’s existing electron storage ring – which will require a year-long shutdown of the APS experimental programme – is now scheduled to kick off in April 2023. That represents a 10-month delay versus the original planned refit owing to the operational impacts of the COVID-19 pandemic. The upgrade of the APS, a national synchrotron research facility funded by the US DOE, will reduce electron beam emittance by a factor of 70 from its present value which, together with a doubling of stored beam current and the introduction of high-performance insertion devices (some superconducting), will yield X-ray beams two to three orders of magnitude brighter than the current machine. Delaying the shutdown for the storage-ring upgrade will allow the APS to continue operating for all three experimental runs in 2022.

• The US DOE’s Brookhaven National Laboratory (BNL) has named Wolfram Fischer as chair of its Collider–Accelerator Department (C-AD). C-AD develops, improves and operates BNL’s suite of particle and heavy-ion accelerators – including the Relativistic Heavy Ion Collider (RHIC) and Alternating Gradient Synchrotron (AGS) – and will also play a key role in supporting the upcoming construction of the Electron-Ion Collider (see Partnership yields big wins for the EIC). Fischer previously served as accelerator division head in C-AD.

The post US accelerator projects: Lab reports appeared first on CERN Courier.

The Proton Improvement Plan II (PIP-II) is an essential upgrade – and ambitious reimagining – of the Fermilab accelerator complex. An all-new, leading-edge superconducting linear accelerator, combined with a comprehensive overhaul of the laboratory’s existing circular accelerators, will deliver multimegawatt proton beam power and, in turn, enable the world’s most intense beam of neutrinos for the international Long Baseline Neutrino Facility (LBNF) and Deep Underground Neutrino Experiment (DUNE). While positioning Fermilab at the forefront of accelerator-based neutrino research, PIP-II will also provide the “engine room” for a diverse – and scalable – experimental programme in US particle physics for decades to come. Put simply, PIP-II will be the highest-energy and highest-power continuous-wave (CW) proton linac ever built, capable of delivering both pulsed and continuous particle beams.

Another unique aspect of PIP-II is that it is the first US Department of Energy (DOE)-funded particle accelerator that will be built with significant international participation. With major “in-kind” contributions from institutions in India, Italy, the UK, France and Poland, the project’s international partners bring wide-ranging expertise and know-how in core accelerator technologies along with an established track-record in big-physics initiatives. What’s more, PIP-II is not going to be the last DOE project to benefit from international collaboration – there will be more to come – so a near-term priority is to provide a successful template that others can follow. 

Deconstructing neutrino physics

Operationally, LBNF/DUNE is a global research endeavour comprising three main parts: the experiment itself (DUNE); the facility that produces the neutrino beam plus associated infrastructure to support the experiment (LBNF); and the PIP-II upgrade to the Fermilab accelerator complex, which will power the neutrino beam. 

At Fermilab, PIP-II will accelerate protons and smash them into an ultrapure graphite target. The resulting beam of neutrinos will travel through the DUNE near detector on the Fermilab site, then through 1300 km of earth (no tunnel required), and finally through the DUNE far detector at Sanford Lab in South Dakota (see figure). Data from neutrino interactions collected by the experiment’s detectors will be analysed by a network of more than 1000 DUNE collaborators around the world.

In this way, DUNE will enable a comprehensive programme of precision neutrino-oscillation measurements using ν_μ and ν_μ beams from Fermilab. Key areas of activity will include tests of leptonic charge-parity conservation; determining the neutrino mass ordering; measuring the angle θ₂₃ in the Pontecorvo–Maki–Nakagawa–Sakata mixing matrix; and probing the three-neutrino paradigm. Furthermore, DUNE will search for proton decay in several decay modes and potentially detect and measure the ν_e flux from any supernovae that take place in our galaxy. 

To provide unprecedented detail in the reconstruction of neutrino events, the DUNE experiment will exploit liquid-argon time-projection-chamber (LArTPC) detectors on a massive scale (technology itself that was first deployed at scale in 2010 for the ICARUS detector as part of the CERN Neutrinos to Gran Sasso facility). The LArTPC implementation for DUNE is currently being developed in two prototype detectors at CERN via the CERN Neutrino Platform, an initiative inaugurated in 2014 following the recommendations of the 2013 European Strategy for Particle Physics to provide a focal point for Europe’s contributions to global neutrino research. 

In addition to the prototype DUNE detectors, the CERN Neutrino Platform is contributing to the long-baseline Tokai-to-Kamioka (T2K) and future Hyper-Kamiokande experiments in Japan. Construction of the underground caverns for DUNE and Hyper-Kamiokande is under way, with both experiments chasing similar physics goals and offering valuable scientific complementarity when they come online towards the end of the decade. 

A key driver of change was the recommendation of the 2014 US Particle Physics Project Prioritization Panel (P5) that the US host a world-leading international programme in neutrino physics. “Its centrepiece,” the P5 report asserts, “would be a next-generation long-baseline neutrino facility (LBNF). LBNF would combine a high-intensity neutrino beam and a large-volume precision detector [DUNE] sited underground a long distance away to make accurate measurements of the oscillated neutrino properties… A powerful, wideband neutrino beam would be realised with Fermilab’s PIP-II upgrade project, which provides very high intensities in the Fermilab accelerator complex.”

Fast forward to December 2020 and full DOE approval of the PIP-II baseline plan, at a total project cost of $978m and with completion scheduled for 2028. Initial site preparation actually started in March 2019, while construction of the cryoplant building got under way in July 2020. Commissioning of PIP-II is planned for the second half of this decade, with the first delivery of neutrino beam to LBNF/DUNE in the late 2020s (see “Deconstructing neutrino physics” panel). With the help of Fermilab’s network of international partners, a highly capable, state-of-the-art accelerator will soon be probing new frontiers in neutrino physics and, more broadly, redefining the roadmap for US high-energy physics.  

Then, now, next

If that’s the future, what of the back-story? Fermilab’s particle-accelerator complex originally powered the Tevatron, the first machine to break the TeV energy barrier and the world’s most powerful accelerator before CERN’s Large Hadron Collider (LHC) came online a decade ago. The Tevatron was shut down in 2011 after three illustrious decades at the forefront of particle physics, with notable high-points including discovery of the top quark in 1995 and direct discovery of the tau neutrino in 2000. 

A powerful, wideband neutrino beam would be realised with Fermilab’s PIP-II upgrade project

Today, about 4000 scientists from more than 50 countries rely on Fermilab’s accelerators, detectors and computing facilities to support their cutting-edge research. The laboratory comprises four interlinking accelerators and storage rings: a 400 MeV room-temperature linac; an 8 GeV Booster synchrotron; an 8 GeV fixed-energy storage ring called the Recycler; and a 60–120 GeV Main Injector synchrotron housed in the same tunnel with the Recycler. The Main Injector generates more than 800 kW of proton beam power, in turn yielding the world’s most intense beams of neutrinos for Fermilab’s flagship NOvA experiment (with the far detector located in Ash River, Minnesota), while supporting a multitude of other research programmes exploring fundamental particles and forces down to the smallest scales.

A leading-edge SRF proton linac

The roll-out of PIP-II will make the Fermilab complex more powerful again. Replacing the 50-year-old linear accelerator with a high-intensity, superconducting radio­frequency (SRF) linac will enable Fermilab to deliver 1.2 MW of proton beam power to the LBNF target, providing a platform for scale-up to multimegawatt levels and the capability for high-power operation across multiple particle-physics experiments simultaneously. 

Deconstructed, the PIP-II linac is an 800 MeV, 2 mA H^– machine consisting of a room-temperature front-end (up to 2.1 MeV) followed by an SRF section designed to operate in CW mode. The CW operation, and the requirements it places on the SRF systems, present some unprecedented challenges in terms of machine design. 

The H^– source (capable of 15 mA beam current) is followed by a low-energy beam transport (LEBT) section and a radio­frequency quadrupole (RFQ) that operates at a frequency of 162.5 MHz and is capable of 10 mA CW operation. The RFQ bunches, focuses and accelerates the beam from 30 keV to 2.1 MeV. Subsequently, the PIP-II MEBT includes a bunch-by-bunch chopping system that removes undesired bunches of arbitrary patterns from the CW beam exiting the RFQ. This is one of several innovative features of the PIP-II linac design that enables not only direct injection into the Booster RF bucket – thereby mitigating beam losses at injection – but also delivery of tailored bunch patterns for other experiments. The chopper system itself comprises a pair of wideband kickers and a 20 kW beam absorber.

In terms of the beam physics, the H^– ions are non-relativistic at 2.1 MeV and their velocity changes rapidly with acceleration along the linac. To achieve efficient acceleration to 800 MeV, the PIP-II linac employs several families of accelerating cavities optimised for specific velocity regimes – i.e. five different types of SRF cavities at three RF frequencies. Although this arrangement ensures efficient acceleration, it also increases the technical complexity of the project owing to the unique challenges associated with the design, fabrication and commissioning of a portfolio of accelerating systems.

Mapped versus increasing energy, the PIP-II linac consists of a half-wave resonator (HWR) operating at 162.5 MHz at optimal beta-value of 0.112; two types of single-spoke resonators (SSR1, SSR2) at 325 MHz and optimal betas equal to 0.222 and 0.472, respectively; and two types of elliptical cavities with low and high beta at 650 MHz (LB650, HB650) and optimal betas equal to 0.65 and 0.971. The HWR cryomodule has been built by the DOE’s Argonne National Laboratory (Lemont, Illinois), while an SSR1 prototype cryomodule was constructed by Fermilab, with a cavity provided by India’s Department of Atomic Energy. Both cryomodules have now been tested successfully with beam by the PIP-II accelerator physics team. 

Innovation yields acceleration

Each of the five accelerating systems comes with unique technical challenges and requires dedicated development to validate performance requirements. In particular, the CW RF mode of operation necessitates SRF cavities with high-quality factors at high gradient, thereby minimising the cryogenic load. For the SSR2, LB650 and HB650 cavities, the Q_o and accelerating gradient specifications are: 0.82 × 10¹⁰ and 11.4 MV/m; 2.4 × 10¹⁰ and 16.8 MV/m; 3.3 × 10¹⁰ and 18.7 MV/m, respectively – figures of merit that are all beyond the current state-of-the-art. Nitrogen doping will enable the elliptical cavities to reach this level of performance, while the SSR2 cavities will undergo a rotational-buffered chemical polishing treatment. 

PIP-II prioritises international partnerships

PIP-II is the first DOE-funded particle accelerator to be built with significant international participation, leveraging in-kind contributions of equipment, personnel and expertise from a network of partners across six countries. It’s a similar working model to that favoured by European laboratories like CERN, the European X-ray Free Electron Laser (XFEL) and the European Spallation Source (ESS) – all of which have shared their experiences with Fermilab to inform the PIP-II partnership programme. 

US

Partners: Argonne National Laboratory; Fermilab (lead partner); Lawrence Berkeley National Laboratory; Thomas Jefferson National Accelerator Facility

Key inputs: HWR, RFQ and resonance control systems

INDIA

Partners: Bhabha Atomic Research Centre (BARC); Inter-University Accelerator Centre (IUAC); Raja Ramanna Centre for Advanced Technology (RRCAT); Variable Energy Cyclotron Centre (VECC)

Key inputs: room-temperature and superconducting magnets, SRF cavities, cryomodules, RF amplifiers

ITALY

Partner: Italian Institute for Nuclear Physics (INFN)

Key inputs: SRF cavities (LB650) 

UK

Partner: Science and Technology Facilities Council as part of UK Research and Innovation (STFC UKRI)

Key inputs: SRF cryomodules (HB650)

FRANCE

Partners: French Alternative Energies and Atomic Energy Commission (CEA); French National Centre for Scientific Research/National Institute of Nuclear and Particle Physics (CNRS/IN2P3) 

Key inputs: cryomodules (LB650) and SRF cavity testing (SSR2)

POLAND

Partners: Wrocław University of Science and Technology; Warsaw University of Technology; Lodz University of Technology

Key inputs: cryogenic distribution systems and high-performance electronics (e.g. low-level RF and RF protection instrumentation).

A further design challenge is to ensure that the cavity resonance is as narrow as possible – something that is necessary to minimise RF power requirements when operating in CW mode. However, a narrow-bandwidth cavity is prone to detuning owing to small acoustic disturbances (so-called microphonic noise), with adverse effects on the required phase, amplitude stability and ultimately RF power consumption. The maximum detuning requirement for PIP-II is 20 Hz – achieved via a mix of passive approaches (e.g. cryomodule design, decoupling cavities from sources of vibration and more rigid cavity design) and active intervention (e.g. adaptive detuning control algorithms). 

Another issue in the pulsed RF regime is Lorentz force cavity detuning, in which the thin walls of the SRF cavities are deformed by forces from electromagnetic fields inside the cavity. This phenomenon can be especially severe in the SSR2 and LB650 cavities – where detuning may be approximately 10 times larger than the cavity bandwidth – though initial operation of PIP-II in CW RF and pulsed beam mode will help to mitigate any detuning effects.

The management of risk 

Given the scale and complexity of the linac development programme, the Fermilab project team has constructed the PIP-II Injector Test facility (also known as PIP2IT) as a systems engineering testbed for PIP-II’s advanced technologies. Completed last year, PIP2IT is a near-full-scale prototype of the linac’s room-temperature front-end, which accelerates protons up to 2.1 MeV, and the first two PIP-II cryomodules (HWR and SSR1) that then take the beam up to about 20 MeV. 

The testbed is all about risk management: on the one hand, validating design choices and demonstrating that core enabling technologies will meet PIP-II performance goals in an operational setting; on the other, ensuring seamless integration of the in-kind contributions (including SRF cavities, magnets and RF amplifiers) from PIP-II’s network of international partners (see “PIP-II prioritises international partnerships”). Beam commissioning in PIP2IT was completed earlier this year, with notable successes versus a number of essential beam manipulations and technology validations including: the PIP-II design beam parameters; the bunch-by-bunch chopping pattern required for injection into the Booster; and acceleration of beam to 17.2 MeV in the first two PIP-II cryomodules. Significant progress was also registered with successful testing of the SRF/cryomodule technologies, first operation of the laser-wire profile monitor, and the application of machine-learning algorithms to align the orbit through the cryomodules. 

There’s no duplication of effort here either. Post-commissioning, after completion of full system and design validation, the PIP2IT accelerator will be disassembled, moved and reinstalled in the PIP-II facility as the SRF linac’s upstream front-end. The testbed location, meanwhile, is being transformed into the PIP-II Cryomodule Test Facility, where most of the cryomodules will be tested with full RF power before being installed in the tunnel. 

Notwithstanding construction of the new SRF linac, PIP-II also involves fundamental upgrades to Fermilab’s existing circular accelerators – the Booster, Recycler Ring and Main Injector – to enable the complex to achieve at least 1.2 MW of proton beam power while providing a scalable platform towards multi-MW capability. More specifically, the path to 1.2 MW from Fermilab’s Main Injector, over the energy range 60 to 120 GeV, requires a number of deliverables to come together: increase of the Fermilab Booster beam intensity by roughly 50% compared to current operation (i.e. an increase in the number of protons extracted per Booster cycle from 4.3 × 10¹² to 6.3 × 10¹²); reduction of the Main Injector cycle from 1.33 to 1.2 s; and an increase of the Booster repetition rate from 15 to 20 Hz. 

Right now, beam losses in the Booster – which occur during injection, transition and extraction – prevent the intensity increase and limit the performance of the accelerator complex to roughly 900 kW. The PIP-II SRF linac injection into the Booster mitigates high-intensity effects and reduces losses on two fronts: first, the higher injection energy (800 MeV vs 400 MeV) will mitigate space-charge forces at higher beam intensities; second, the high-quality, lower-emittance beam will allow “beam painting” at injection in all three degrees of freedom, further reducing space-charge forces and beam losses at high intensity. Other upgrades are also in the works to further reduce and control losses, with some of them to be made available early, several years before PIP-II commissioning, to benefit the NOvA experiment. 

In PIP-II, the 8 GeV Booster beam will be injected into the Fermilab Recycler ring – equipped with new 53 MHz RF cavities capable of larger beam current – where 12 Booster transfer batches are accumulated and slip-stacked. Next, the Recycler beam will enter Fermilab’s Main Injector – equipped with double the number of power amplifiers and vacuum tubes – which accelerates this intense beam anywhere from 60 to 120 GeV, delivering at least 1.2 MW of beam power at 120 GeV. Further, the Booster upgrade to 20 Hz will support an 8 GeV science programme, including Fermilab’s muon-to-electron conversion experiment (Mu2e) and studies of short-baseline neutrinos (see “PIP-II: a flexible, versatile design”). 

International collaboration  

Over the next decade, the PIP-II roadmap is clear. Phase one of the project will see the front-end of the Fermilab accelerator complex replaced with an 800 MeV SRF linac while performing necessary upgrades to the existing rings. Completion will see PIP-II deliver an initial beam power of 1.2 MW on the LBNF target, though the longer-term objective is to upgrade to 2.4 MW through replacement of the Booster synchrotron.

Operationally, it’s worth reiterating that PIP-II is very much a collective endeavour

Operationally, it’s worth reiterating that PIP-II is very much a collective endeavour – in fact, the first US accelerator to be built with the help of a network of international partnerships. In this way, PIP-II is very much a trail-blazer, with the excellence and sustained commitment of the project’s international partners essential for the construction – and ultimately the successful delivery – of this next-generation accelerator complex by the end of the decade. 

The post PIP-II’s international engagement is the secret of success appeared first on CERN Courier.

The $730 million Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU) is scheduled to come online in early 2022 – a game-changer in every sense for the US and international nuclear-physics communities. With peer review and approval of the first round of experimental proposals now complete, an initial cohort of scientists from 25 countries is making final preparations to exploit FRIB’s unique capabilities. Their goal: to open up new frontiers in the fundamental study of rare and unstable isotopes as well as identifying promising candidate isotopes for real-world applications. 

The engine-room of the FRIB scientific programme is an all-new 400 kW superconducting radiofrequency (SRF) linac. In short: the world’s most powerful heavy-ion driver accelerator, firing beams of stable isotopes at targets of heavier nuclei (for example, carbon or beryllium). Amid the chaos of flying particles, two nuclei will occasionally collide, fusing to form a rare and unstable isotope – a process that ultimately delivers high-intensity beams of rare isotopes to FRIB’s experimental end-stations and a suite of scientific instruments. 

Funded by the US Department of Energy Office of Science (DOE-SC), and supported by MSU cost-share and contributions, FRIB will operate as a traditional big-science user facility, with beam-time granted via merit review of proposals and access open to all interested researchers. Here, FRIB’s scientific director, Bradley Sherrill, tells CERN Courier how the laboratory is gearing up for “go-live” and the importance of wide-ranging engagement with the international user community, industry and other rare-isotope facilities.

What are the overarching objectives of the FRIB scientific mission?

There are four main strands to the FRIB science programme. For starters, user experiments will generate a wealth of data to advance our understanding of the nucleus – how it’s put together and how we can develop theoretical nuclear models and their approximations. At the same time, the research programme will yield unique insights on the origins of the chemical elements in the universe, providing access to most of the rare isotopes involved in extreme astrophysical processes such as supernovae and neutron-star mergers. Other scientists, meanwhile, will use isotopes produced at FRIB to devise experiments that look beyond the Standard Model, searching for subtle indications of hidden interactions and minutely broken symmetries. Finally, FRIB will generate research quantities of rare isotopes to feed into R&D efforts on next-generation applications – from functional medical imaging to safer nuclear reactors and advanced detector technologies.

What is FRIB’s biggest differentiator?  

The 400 kW SRF linac is the heart of FRIB’s value proposition to the research community, opening up access to a much broader spectrum of rare isotopes than hitherto possible – in fact, approximately 80% of the isotopes predicted to exist. It is worth noting, though, that FRIB does not exist in isolation. It’s part of a global research ecosystem, with a network of collaborations ongoing with other rare-isotope facilities – among them RIKEN’s RI Beam Factory in Japan, RAON in Korea, ISOLDE at CERN, FAIR in Germany, GANIL in France and ISAC at TRIUMF in Canada. Collectively, FRIB and this global network of laboratories are well placed to deliver unprecedented – and complementary – advances across the nuclear-science landscape over the coming decades.

Is it realistic to expect broader commercial opportunities to emerge from FRIB’s research programme? 

There’s a high likelihood of FRIB yielding spin-off technologies and commercial applications down the line. One of the game-changers with FRIB is the quantities of rare isotopes the beamline can produce with high efficiency – a production scheme that enables us to make a broad swathe of isotopes relatively quickly and with high purity. That capability, in turn, will enable potential early-adopters in industry to fast-track the evaluation of novel applications and, where appropriate, to figure out how to produce the isotopes of interest at scale (see “FRIB’s bumper harvest will fuel applied science and innovation”). 

How is FRIB engaging with the scientific user community across academia, industry and government agencies? 

FRIB enjoys strong links with its future users – both here in the US and internationally – and meets with them regularly at planning events to identify and coordinate research opportunities. Earlier this year, in response to our first call for proposals, we received 82 project submissions and six letters of intent from 130 institutions across 30 countries. Those science proposals were subsequently peer-reviewed by the FRIB Programme Advisory Committee (PAC), an international group of nuclear science experts which I convene, to yield an initial set of experiments that will get underway once FRIB commences user operations in early 2022. 

Those PAC-recommended experiments align with national science priorities across the four FRIB priority areas: properties of rare isotopes; nuclear astrophysics; fundamental interactions; and applications for society. The headline numbers saw 34 (out of 82 requested) experiments approved with a projected 4122 facility-use hours. There are 88 institutions, 24 US states and 25 countries represented in the initial experimental programme.

What are the opportunities for early-career scientists and engineers at FRIB?

Developing the talent pipeline is part of the organisational DNA here at FRIB. There’s a structured educational framework to pass on the expertise and experience of senior FRIB staff to the next generation of researchers, engineers and technicians in nuclear science. MSU’s Accelerator Science and Engineering Traineeship (ASET) programme is a case in point. ASET leverages multidisciplinary expertise from FRIB and MSU colleagues to support specialisation in four key areas: physics and engineering of large accelerators; SRF technology; radiofrequency power engineering; and large-scale cryogenic systems. 

There’s a high likelihood of FRIB yielding new spin-off technologies as well as commercial applications

Many MSU ASET students supplement their courses through participation in the US Particle Accelerator School, a national programme that provides graduate-level training and workforce development in the science of particle beams and associated accelerator technologies. At a more specialist level, there’s also the MSU Cryogenic Initiative, a unique educational collaboration between the university’s college of engineering and FRIB’s cryogenics team. Meanwhile, we continue to prioritise development of a more diverse workforce, partnering with several academic institutions that traditionally serve under-represented groups to broaden participation in the FRIB programme. 

In what ways does FRIB ensure a best-practice approach to facilities management? 

Sustainability and continuous improvement underpin all FRIB working practices. We are an ISO14001-registered organisation, which means we measure ourselves against an international standard specifying requirements for effective environmental management. That’s reflected, for example, in our use of energy-efficient superconducting technologies, and also our efforts to minimise any helium wastage through an exhaustive capture, recovery and reuse scheme within FRIB’s cryogenic plant. 

We also have an ISO 9001-registered quality management system that guides how we address scientific user needs; an ISO 45001-registered occupational health and safety management system to keep our workers safe; and an ISO 27001-registered information security management system.

How important is FRIB’s relationship with industry?

Our strategic partnerships with industry are also significant in driving organisational efficiencies. The use of standard industry components wherever possible reduces maintenance and training requirements, minimises the need for expensive product inventory, and lowers our operational costs. We engage with manufacturers on a co-development basis, fast-tracking innovation and knowledge transfer so that they are able to produce core enabling technologies for FRIB at scale – whether that’s accelerator cavities, superconducting magnets, or vacuum and cryogenic subsystems.  

The post Rare isotopes aplenty at FRIB appeared first on CERN Courier.

An ambitious upgrade of the US’s flagship X-ray free-electron-laser facility – the Linac Coherent Light Source (LCLS) at the SLAC National Accelerator Laboratory in California – is nearing completion. Set for “first light” in 2022, LCLS-II will deliver X-ray laser beams that are 10,000 times brighter than LCLS at repetition rates of up to a million pulses per second – generating more X-ray pulses in just a few hours than the current laser has delivered through the course of its 12-year operational lifetime. The cutting-edge physics of the new X-ray laser – underpinned by a cryogenically cooled superconducting radiofrequency (SRF) linac – will enable the two beams from LCLS and LCLS-II to work in tandem. This, in turn, will help researchers observe rare events that happen during chemical reactions and study delicate biological molecules at the atomic scale in their natural environments, as well as potentially shed light on exotic quantum phenomena with applications in next-generation quantum computing and communications systems. 

Strategic commitment

Successful delivery of the LCLS-II linac was possible thanks to a multicentre collaborative effort involving US national and university laboratories, following the decision to pursue an SRF-based machine in 2014 through the design, assembly, test, transportation and installation of a string of 37 SRF cryomodules (most of them more than 12 m long) into the SLAC tunnel (see figures “Tunnel vision” and “Keeping cool”). All told, this non-trivial undertaking necessitated the construction of 40 1.3 GHz SRF cryomodules (five of them spares) and three 3.9 GHz cryomodules (one spare) – with delivery of approximately one cryomodule per month from February 2019 until December 2020 to allow completion of the LCLS-II linac installation on schedule by November 2021. 

This industrial-scale programme of works was shaped by a strategic commitment, early on in the LCLS-II design phase, to transfer, and ultimately iterate, the established SRF capabilities of the European XFEL project into the core technology platform used for the LCLS-II SRF cryomodules. Put simply: it would not have been possible to complete the LCLS-II project, within cost and on schedule, without the sustained cooperation of the European XFEL consortium – in particular, colleagues at DESY (Germany), CEA Saclay (France) and several other European laboratories (as well as KEK in Japan) that generously shared their experiences and know-how so that the LCLS-II collaboration could hit the ground running. 

Better together 

These days, large-scale accelerator or detector projects are very much a collective endeavour. Not only is the sprawling scope of such projects beyond a single organisation, but the risks of overspend and slippage can greatly increase with a “do-it-on-your-own” strategy. When the LCLS-II project opted for an SRF technology pathway in 2014 (to maximise laser performance and future-proofing), the logical next step was to build a broad-based coalition with other US Department of Energy (DOE) national laboratories and universities. In this case, SLAC, Fermilab, Jefferson Lab (JLab) and Cornell University contributed expertise for cryomodule production, while Argonne National Laboratory and Lawrence Berkeley National Laboratory managed delivery of the undulators and photoinjector for the project. For sure, the start-up time for LCLS-II would have increased significantly without this joint effort, extending the overall project by several years.

Each partner brought something unique to the LCLS-II collaboration. While SLAC was still a relative newcomer to SRF technologies, the lab had a management team that was familiar with building large-scale accelerators (following successful delivery of the LCLS). The priority for SLAC was therefore to scale up its small nucleus of SRF experts by recruiting experienced SRF technologists and engineers to the staff team. 

In contrast, the JLab team brought an established track-record in the production of SRF cryomodules, having built its own machine, the Continuous Electron Beam Accelerator Facility (CEBAF), as well as cryomodules for the Spallation Neutron Source (SNS) linac at Oak Ridge National Laboratory in Tennessee. Cornell, too, came with a rich history in SRF R&D – capabilities that, in turn, helped to solidify the SRF cavity preparation process for LCLS-II. 

Finally, Fermilab had, at the time, recently built two cutting-edge cryomodules of the same style as that chosen for LCLS-II. To fabricate these modules, Fermilab worked closely with the team at DESY to set up the same type of production infrastructure used on the European XFEL. From that perspective, the required tooling and fixtures were all ready to go for the LCLS-II project. While Fermilab was the “designer of record” for the SRF cryomodule, with primary responsibility for delivering a working design to meet LCLS-II requirements, the realisation of an optimised technology platform was, in large part, a team effort involving SRF experts from across the collaboration.

Challenges are inevitable when developing new facilities at the limits of known technology

Operationally, the use of two facilities to produce the SRF cryomodules – Fermilab and JLab – ensured a compressed delivery schedule and increased flexibility within the LCLS-II programme. On the downside, the dual-track production model increased infrastructure costs (with the procurement of duplicate sets of tooling) and meant additional oversight to ensure a standardised approach across both sites. Ongoing procurements were divided equally between Fermilab and JLab, with deliveries often made to each lab directly from the industry suppliers. Each facility, in turn, kept its own inventory of parts, so as to minimise interruptions to cryomodule assembly owing to any supply-chain issues (and enabling critical components to be transferred between labs as required). What’s more, the close working relationship between Fermilab and JLab kept any such interruptions to a minimum.

Collective problems, collective solutions 

While the European XFEL provided the template for the LCLS-II SRF cryomodule design, several key elements of the LCLS-II approach subsequently evolved to align with the CW operation requirements and the specifics of the SLAC tunnel. Success in tackling these technical challenges – across design, assembly, testing and transportation of the cryomodules – is testament to the strength of the LCLS-II collaboration and the collective efforts of the participating teams in the US and Europe. 

For starters, the thermal performance specification of the SRF cavities exceeded the state-of-the-art and required development and industrialisation of the concept of nitrogen doping (a process in which SRF cavities are heat-treated in a nitrogen atmosphere to increase their cryogenic efficiency and, in turn, lower the overall operating costs of the linac). The nitrogen-doping technique was invented at Fermilab in 2012 but, prior to LCLS-II construction, had been used only in an R&D setting.

Adapatability in real-time 

The priority was clear: to transfer the nitrogen-doping capability to LCLS-II’s industry partners, so that the cavity manufacturers could perform the necessary materials processing before final helium-vessel jacketing. During this knowledge transfer, it was found that nitrogen-doped cavities are particularly sensitive to the base niobium sheet material – something the collaboration only realised once the cavity vendors were into full production. This resulted in a number of process changes for the heat treatment temperature, depending on which material supplier was used and the specific properties of the niobium sheet deployed in different production runs. JLab, for its part, held the contract for the cavities and pulled out all stops to ensure success.

At the same time, the conversion from pulsed to CW operation necessitated a faster cooldown cycle for the SRF cavities, requiring several changes to the internal piping, a larger exhaust chimney on the helium vessel, as well as the addition of two new cryogenic valves per cryomodule. Also significant is the 0.5% slope in the longitudinal floor of the existing SLAC tunnel, which dictated careful attention to liquid-helium management in the cryomodules (with a separate two-phase line and liquid-level probes at both ends of every module). 

However, the biggest setback during LCLS-II construction involved the loss of beamline vacuum during cryomodule transport. Specifically, two cryomodules had their beamlines vented and required complete disassembly and rebuilding – resulting in a five-month moratorium on shipping of completed cryomodules in the second half of 2019. It turns out that a small, what was thought to be inconsequential, change in a coupler flange resulted in the cold coupler assembly being susceptible to resonances excited by transport. The result was a bellows tear that vented the beamline. Unfortunately, initial “road-tests” with a similar, though not exactly identical, prototype cryomodule had not surfaced this behaviour. 

Shine on: from LCLS-II to LCLS-II HE

As with many accelerator projects, LCLS-II is not an end-point in itself, more an evolutionary transition within a longer term development roadmap. In fact, work is already under way on LCLS-II HE – a project that will increase the energy of the CW SRF linac from 4 to 8 GeV, enabling the photon energy range to be extended to at least 13 keV, and potentially up to 20 keV at 1 MHz repetition rates. 

To ensure continuity of production for LCLS-II HE, 25 next-generation cryomodules are in the works, with even higher performance specifications versus their LCLS-II counterparts, while upgrades to the source and beam transport are also being finalised. 

In addition to LCLS-II HE, other SRF disciplines will benefit from the R&D and technological innovation that has come out of the LCLS-II construction programme. SRF technologies are constantly evolving and advancing the state-of-the-art, whether that’s in single-cavity cryogen-free systems, additional FEL CW upgrades to existing machines, or the building blocks that will underpin enormous new machines like the proposed International Linear Collider. 

Such challenges are inevitable when developing new facilities at the limits of known technology. In the end, the problem was successfully addressed using the diverse talents of the collaboration to brainstorm solutions, with the available access ports allowing an elastomer wedge to be inserted to secure the vulnerable section. A key take-away here is the need for future projects to perform thorough transport analysis, verify the transport loads using mock-ups or dummy devices, and install adequate instrumentation to ensure granular data analysis before long-distance transport of mission-critical components. 

Upon completion of the assembly phase, all LCLS-II cryo-modules were subsequently tested at either Fermilab or JLab, with one module tested at both locations to ensure reproducibility and consistency of results. For high Q₀ performance in nitrogen-doped cavities, cooldown flow rates of at least 30 g/s of liquid helium were found to give the best results, helping to expel magnetic flux that could otherwise be trapped in the cavity. 

Overall, cryomodule performance on the test stands exceeded specifications, with an average energy gain per cryomodule of 158 MV (versus specification of 128 MV) and average Q₀ of 3 × 10¹⁰ (versus specification of 2.7 × 10¹⁰). Looking ahead, attention is already shifting to the real-world cryomodule performance in the SLAC tunnel – something that will be measured for the first time in 2022.

Transferable lessons

For all members of the collaboration working on the LCLS-II cryomodules, this challenging project holds many lessons. Most important is the nature of collaboration itself, building a strong team and using that strength to address problems in real-time as they arise. The mantra “we are all in this together” should be front-and-centre for any multi-institutional scientific endeavour – as it was in this case. With all parties making their best efforts, the goal should be to utilise the combined strengths of the collaboration to mitigate challenges. Solutions need to be thought of in a more global sense, since the best answer might mean another collaborator taking more onto their plate. Collaboration implies true partnership and a working model very different to a transactional customer–vendor relationship.

Collaboration implies true partnership and a working model very different to a transactional relationship

From a planning perspective, it’s vital to ensure that the initial project cost and schedule are consistent with the technical challenges and preparedness of the infrastructure. Prototypes and pre-series production runs reduce risk and cost in the long term and should be part of the plan, but there must be sufficient time for data analysis and changes to be made after a prototype run in order for it to be useful. Time spent on detailed technical reviews is also time well spent. New designs of complex components need detailed oversight and review, and should be controlled by a team, rather than a single individual, so that sign-off on any detailed design changes are made by an informed collective. 

Planning ahead

Work planning and control is another essential element for success and safety. This idea needs to be built into the “manufacturing system”, including into the cost and schedule, and be part of each individual’s daily checklist. No one disagrees with this concept, but good intentions on their own will not suffice. As such, required safety documentation should be clear and unambiguous, and be reviewed by people with relevant expertise. Production data and documentation need to be collected, made easily available to the entire project team, and analysed regularly for trends, both positive and negative. 

Supply chain, of course, is critical in any production environment – and LCLS-II is no exception. When possible, it is best to have parts procured, inspected, accepted and on-the-shelf before production begins, thereby eliminating possible workflow delays. Pre-stocking also allows adequate time to recycle and replace parts that do not meet project specifications. Also worth noting is that it’s often the smaller components – such as bellows, feedthroughs and copper-plated elements – that drive workflow slowdowns. A key insight from LCLS-II is to place purchase orders early, stay on top of vendor deliveries, and perform parts inspections as soon as possible post-delivery. Projects also benefit from having clearly articulated pass/fail criteria and established procedures for handling non-conformance – all of which alleviates the need to make critical go/no-go acceptance decisions in the face of schedule pressures.

Finally, it’s worth highlighting the broader impact – both personal and professional – to individual team members participating on a big-science collaboration like LCLS-II. At the end of the build, what remained after designs were completed, problems solved, production rates met, and cryomodules delivered and installed, were the friendships that had been nurtured over several years. The collaboration amongst partners, both formal and informal, who truly cared about the project’s success, and had each other’s backs when there were issues arising: these are the things that solidified the mutual respect, the camaraderie and, in the end, made LCLS-II such a rewarding project.

The post ‘First light’ beckons as LCLS-II gears up appeared first on CERN Courier.

The international nuclear-physics community will be front-and-centre as a unique research facility called the Electron–Ion Collider (EIC) moves from concept to reality through the 2020s – the latest progression in the line of large-scale accelerator programmes designed to probe the fundamental forces and particles that underpin the structure of matter. 

Decades of research in particle and nuclear physics have shown that protons and neutrons, once thought to be elementary, have a rich, dynamically complex internal structure of quarks, anti-quarks and gluons, the understanding of which is fundamental to the nature of matter as we experience it. By colliding high-energy beams of electrons with high-energy beams of protons and heavy ions, the EIC is designed to explore this hidden subatomic landscape with the resolving power to image its behaviour directly. Put another way: the EIC will provide the world’s most powerful microscope for studying the “glue” that binds the building blocks of matter.

Luminous performance

When the EIC comes online in the early 2030s, the facility will perform precision “nuclear femtography” by zeroing in on the substructure of quarks and gluons in a manner comparable to the seminal studies of the proton using electron–proton collisions at DESY’s HERA accelerator in Germany between 1992 and 2007 (see “Nuclear femtography to delve deep into nuclear matter” panel). However, the EIC will produce a luminosity (collision rate) 100 times greater than the highest achieved by HERA and, for the first time in such a collider, will provide spin-polarised beams of both protons and electrons, as well as high-energy collisions of electrons with heavy ions. All of which will require unprecedented performance in terms of the power, intensity and spatial precision of the colliding beams, with the EIC expected to provide not only transformational advances in nuclear science, but also transferable technology innovations to shape the next generation of particle accelerators and detectors.

The US Department of Energy (DOE) formally initiated the EIC project in December 2019 with the approval of a “mission need”. That was followed in June of this year with the next “critical decision” to proceed with funding for engineering and design prior to construction (with the estimated cost of the build about $2 billion). The new facility will be sited at Brookhaven National Laboratory (BNL) in Long Island, New York, utilising components and infrastructure from BNL’s Relativistic Heavy Ion Collider (RHIC), including the polarised proton and ion-beam capability and the 3.8 km underground tunnel. Construction will be carried out as a partnership between BNL and Thomas Jefferson National Accelerator Facility (JLab) in Newport News, Virginia, home of the Continuous Electron Beam Accelerator Facility (CEBAF), which has pioneered many of the enabling technologies needed for the EIC’s new electron rings. 

Beyond the BNL–JLab partnership, the EIC is very much a global research endeavour. While the facility is not scheduled to become operational until early in the next decade, an international community of scientists is already hard at work within the EIC User Group. Formed in 2016, the group now has around 1300 members – representing 265 universities and laboratories from 35 countries – engaged collectively on detector R&D, design and simulation as well as initial planning for the EIC’s experimental programme. 

A cutting-edge accelerator facility

Being the latest addition to the line of particle colliders, the EIC represents a fundamental link in the chain of continuous R&D, knowledge transfer and innovation underpinning all manner of accelerator-related technologies and applications – from advanced particle therapy systems for the treatment of cancer to ion implantation in semiconductor manufacturing. 

The images “The EIC in outline” and “Going underground” show the planned layout of the EIC, where the primary beams circulate inside the existing RHIC tunnel to enable the collisions of high-energy (5–18 GeV) electrons (and possibly positrons) with high-energy ion beams of up to 275 GeV/nucleon. One thing is certain: the operating parameters of the EIC, with luminosities of up to 10³⁴ cm^–2 s^–1 and up to 85% beam polarisation, will push the design of the facility beyond the limits set by previous accelerator projects in a number of core technology areas.

For starters, the EIC will require significant advances in the field of superconducting radiofrequency (SRF) systems operating under high current conditions, including control of higher-order modes, beam RF stability and crab cavities. A major challenge is the achievement of strong cooling of intense proton and light-ion beams to manage emittance growth owing to intrabeam scattering. Such a capability will require unprecedented control of low-energy electron-beam quality with the help of ultrasensitive and precise photon detection technologies – innovations that will likely yield transferable benefits for other areas of research reliant on electron-beam technology (e.g. free-electron lasers). 

The EIC design for strong cooling of the ion beams specifies a superconducting energy-recovery linac with a virtual beam power of 15 MW, an order-of-magnitude increase versus existing machines. With this environmentally friendly new technology, the rapidly cycling beam of low-energy electrons (150 MeV) is accelerated within the linac and passes through a cooling channel where it co-propagates with the ions. The cooling electron beam is then returned to the linac, timed to see the decelerating phase of the RF field, and the beam power is thus recovered for the next accelerating cycle – i.e. beam power is literally recycled after each cooling pass.

The EIC will also require complex operating schemes. A case in point: fresh, highly polarised electron bunches will need to be frequently injected into the electron storage ring without disturbing the collision operation of previously injected bunches. Further complexity comes in maximising the luminosity and polarisation over a large range of centre-of-mass energies and for the entire spectrum of ion beams. With a control system that can monitor hundreds of beam parameters in real-time, and with hundreds of points where the guiding magnetic fields can be tuned on the fly, there is a vast array of “knobs-to-be-turned” to optimise overall performance. Inevitably, this is a facility that will benefit from the use of artificial intelligence and machine-learning technologies to maximise its scientific output. 

At the same time, the EIC and CERN’s High-Luminosity LHC user communities are working in tandem to realise more capable technologies for particle detection as well as innovative electronics for large-scale data read-out and processing. Exploiting advances in chip technology, with feature sizes as small as 65 nm, multipixel silicon sensors are in the works for charged-particle tracking, offering single-point spatial resolution better than 5 µm, very low mass and on-chip, individual-pixel readout. These R&D efforts open the way to compact arrays of thin solid-state detectors with broad angular coverage to replace large-volume gaseous detectors. 

Coupled with leading-edge computing capabilities, such detectors will allow experiments to stream data continuously, rather than selecting small samples of collisions for readout. Taken together, these innovations will yield no shortage of downstream commercial opportunities, feeding into next-generation medical imaging systems, for example, as well as enhancing industrial R&D capacity at synchrotron light-source facilities.

The BNL–JLab partnership

As the lead project partners, BNL and JLab have a deep and long-standing interest in the EIC programme and its wider scientific mission. In 2019, BNL and JLab each submitted their own preconceptual designs to DOE for a future high-energy and high-luminosity polarised EIC based around existing accelerator infrastructure and facilities. In January 2020, DOE subsequently selected BNL as the preferred site for the EIC, after which the two labs immediately committed to a full partnership between their respective teams (and other collaborators) in the construction and operation of the facility. 

Nuclear femtography to delve deep into nuclear matter

Nuclear matter is inherently complex because the interactions and structures therein are inextricably mixed up: its constituent quarks are bound by gluons that also bind themselves. Consequently, the observed properties of nucleons and nuclei, such as their mass and spin, emerge from a dynamical system governed by quantum chromodynamics (QCD). The quark masses, generated via the Higgs mechanism, only account for a tiny fraction of the mass of a proton, leaving fundamental questions about the role of gluons in the structure of nucleons and nuclei still unanswered. 

The underlying nonlinear dynamics of the gluon’s self-interaction is key to understanding QCD and fundamental features of the strong interactions such as dynamical chiral symmetry-breaking and confinement. Yet despite the central role of gluons, and the many successes in our understanding of QCD, the properties and dynamics of gluons remain largely unexplored. 

If that’s the back-story, the future is there to be written by the EIC, a unique machine that will enable physicists to shed light on the many open questions in modern nuclear physics. 

Back to basics

At the fundamental level, the way in which a nucleon or nucleus reveals itself in an experiment depends on the kinematic regime being probed. A dynamic structure of quarks and gluons is revealed when probing nucleons and nuclei at higher energies, or with higher resolutions. Here, the nucleon transforms from a few-body system, with its structure dominated by three valance quarks, to a regime where it is increasingly dominated by gluons generated through gluon radiation, as discovered at the former HERA electron–proton collider at DESY. Eventually, the gluon density becomes so large that the gluon radiation is balanced by gluon recombination, leading to nonlinear features of the strong interaction.

The LHC and RHIC have shown that neutrons and protons bound inside nuclei already exhibit the collective behaviour that reveals QCD substructure under extreme conditions, as initially seen with high-energy heavy-ion collisions. This has triggered widespread interest in the study of the strong force in the context of condensed-matter physics, and the understanding that the formation and evolution of the extreme phase of QCD matter is dominated by the properties of gluons at high density.

The subnuclear genetic code

The EIC will enable researchers to go far beyond the present one-dimensional picture of nuclei and nucleons, where the composite nucleon appears as a bunch of fast-moving (anti-)quarks and gluons whose transverse momenta or spatial extent are not resolved. Specifically, by correlating the information of the quark and gluon longitudinal momentum component with their transverse momentum and spatial distribution inside the nucleon, the EIC will enable nuclear femtography. 

Such femtographic images will provide, for the first time, insight into the QCD dynamics inside hadrons, such as the interplay between sea quarks and gluons. The ultimate goal is to experimentally reconstruct and constrain the so-called Wigner functions – the quantities that encode the complete tomographic information and constitute a QCD “genetic map” of nucleons and nuclei.

 • Adapted from “Electron–ion collider on the horizon” by Elke-Caroline Aschenauer, BNL, and Rolf Ent, JLab.

The construction project is led by a joint BNL–JLab management team that integrates the scientific, engineering and management capabilities of JLab into the BNL design effort. JLab, for its part, leads on the design and construction of SRF and cryogenics systems, the energy-recovery linac and several of the electron injector and storage-ring subsystems within the EIC accelerator complex. 

More broadly, BNL and JLab are gearing up to work with US and international partners to meet the technical challenges of the EIC in a cost-effective, environmentally responsible manner. The goal: to deliver a leading-edge research facility that will build upon the current CEBAF and RHIC user base to ensure engagement – at scale – from the US and international nuclear-physics communities. 

As such, the labs are jointly hosting the EIC experiments in the spirit of a DOE user facility for fundamental research, while the BNL–JLab management team coordinates the engagement of other US and international laboratories into a multi-institutional partnership for EIC construction. Work is also under way with prospective partners to define appropriate governance and operating structures to enhance the engagement of the user community with the EIC experimental programme. 

With international collaboration hard-wired into the EIC’s working model, the EIC User Group has been in the vanguard of a global effort to develop the science goals for the facility – as well as the experimental programme to realise those goals. Most importantly, the group has carried out intensive studies over the past two years to document the measurements required to deliver EIC’s physics objectives and the resulting detector requirements. This work also included an exposition of evolving detector concepts and a detailed compendium of candidate technologies for the EIC experimental programme.

Cornerstone collaborations 

The resulting Yellow Report, released in March 2021, provides the basis for the ongoing discussion of the most effective implementation of detectors, including the potential for complementary detectors in the two possible collision points as a means of maximising the scientific output of the EIC facility (see “Detectors deconstructed”). Operationally, the report also provides the cornerstone on which EIC detector proposals are currently being developed by three international “proto-collaborations”, with significant components of the detector instrumentation being sourced from non-US partners. 

The EIC represents a fundamental link in the chain of continuous R&D and knowledge transfer

Along every coordinate, it’s clear that the EIC project profits enormously from its synergies with accelerator and detector R&D efforts worldwide. To reinforce those benefits, a three-day international workshop was held in October 2020, focusing on EIC partnership opportunities across R&D and construction of accelerator components. This first Accelerator Partnership Workshop, hosted by the Cockcroft Institute in the UK, attracted more than 250 online participants from 26 countries for a broad overview of EIC and related accelerator-technology projects. A follow-up workshop, scheduled for October 2021 and hosted by the TRIUMF Laboratory in Canada, will focus primarily on areas where advanced “scope of work” discussions are already under way between the EIC project and potential partners.

Nurturing talent 

While discussion and collaboration between the BNL and JLab communities were prioritised from the start of the EIC planning process, a related goal is to get early-career scientists engaged in the EIC physics programme. To this end, two centres were created independently: the Center for Frontiers in Nuclear Science (CFNS) at Stony Brook University, New York, and the Electron-Ion Collider Center (EIC²) at JLab.

The CFNS, established jointly by BNL and Stony Brook University in 2017, was funded by a generous donation from the Simons Foundation (a not-for-profit organisation that supports basic science) and a grant from the State of New York. As a focal point for EIC scientific discourse, the CFNS mentors early-career researchers seeking long-term opportunities in nuclear science while simultaneously supporting the formation of the EIC’s experimental collaborations. 

Core CFNS activities include EIC science workshops, short ad-hoc meetings (proposed and organised by members of the EIC User Group), alongside a robust postdoctoral fellow programme to guide young scientists in EIC-related theory and experimental disciplines. An annual summer school series on high-energy QCD also kicked off in 2019, with most of the presentations and resources from the wide-ranging CFNS events programme available online to participants around the world. 

In a separate development, the CFNS recently initiated a dedicated programme for under-represented minorities (URMs). The Edward Bouchet Initiative provides a broad portfolio of support to URM students at BNL, including grants to pursue masters or doctoral degrees at Stony Brook on EIC-related research. 

Meanwhile, the EIC² was established at JLab with funding from the State of Virginia to involve outstanding JLab students and postdocs in EIC physics. Recognising that there are many complementary overlaps between JLab’s current physics programme and the physics of the future EIC, the EIC² provides financial support to three PhD students and three postdocs each year to expand their current research to include the physics that will become possible once the new collider comes online. 

Beyond their primary research projects, this year’s cohort of six EIC² fellows worked together to organise and establish the first EIC User Group Early Career workshop. The event, designed specifically to highlight the research of young scientists, was attended by more than 100 delegates and is expected to become an annual part of the EIC User Group meeting.

The future, it seems, is bright, with CFNS and EIC² playing their part in ensuring that a diverse cadre of next-generation scientists and research leaders is in place to maximise the impact of EIC science over the decades to come.

The post Partnership yields big wins for the EIC appeared first on CERN Courier.

CERN surveyors have performed the first geodetic measurements for a possible Future Circular Collider (FCC), a prerequisite for high-precision alignment of the accelerator’s components. The millimetre-precision measurements are one of the first activities undertaken by the FCC feasibility study, which was launched last year following the recommendation of the 2020 update of the European strategy for particle physics. During the next three years, the study will explore the technical and financial viability of a 100 km collider at CERN, for which the tunnel is a top priority. Geology, topography and surface infrastructure are the key constraints on the FCC tunnel’s position, around which civil engineers will design the optimal route, should the project be approved.

The FCC would cover an area about 10 times larger than the LHC, in which every geographical reference must be pinpointed with unprecedented precision. To provide a reference coordinate system, in May the CERN surveyors, in conjunction with ETH Zürich, the Federal Office of Topography Swisstopo, and the School of Engineering and Management Vaud, performed geodetic levelling measurements along an 8 km profile across the Swiss–French border south of Geneva.

Such measurements have two main purposes. The first is to determine a high-precision surface model, or “geoid”, to map the height above sea level in the FCC region. The second purpose is to improve the present reference system, whose measurements date back to the 1980s when the tunnel housing the LHC was built.

“The results will help to evaluate if an extrapolation of the current LHC geodetic reference systems and infrastructure is precise enough, or if a new design is needed over the whole FCC area,” says Hélène Mainaud Durand, group leader of CERN’s geodetic metrology group.

The FCC feasibility study, which involves more than 140 universities and research institutions from 34 countries, also comprises technological, environmental, engineering, political and economic considerations. It is due to be completed by the time the next strategy update gets under way in the middle of the decade. Should the outcome be positive, and the project receive the approval of CERN’s member states, civil-engineering works could start as early as the 2030s.

The post Surveyors eye up a future collider appeared first on CERN Courier.

In physics operation since 2019, SuperKEKB is an innovative nanobeam, asymmetric-energy accelerator complex that collides 7 GeV electrons with 4 GeV positrons, sitting mostly on or near the ϒ(4S) resonance. It uses a large crossing angle and strong focusing at the interaction point (β*_y = 1 mm), and has implemented a crab-waist scheme to stabilise beam–beam blowup using carefully tuned sextupole magnets on either side of the interaction point. These innovations have enabled the SuperKEKB team to attain record luminosities with rather modest beam currents: 0.8 A in the low-energy positron ring and 0.7 A in the high-energy electron ring – a product of beam currents 3.5 times smaller than were used at KEKB when its record luminosity was achieved.