Jobs – Page 3 of 530 – CERN Courier

Accelerators feel the chill

**Cooling the stack** A kicker inside the Antiproton Accumulator at CERN, where stochastic cooling compressed antiprotons into the dense beams that led to the W and Z discovery. Credit: CERN

The monograph Stochastic Cooling of Particle Beams, by Dieter Möhl, is a remarkably thorough treatment of a technique that remains central to hadron-beam physics decades after its invention at CERN. In accelerator physics, cooling means reducing the spread of particle positions and momenta around the design orbit, and stochastic cooling does so by sensing each deviation at a pickup electrode and applying a corrective kick downstream. By enabling the accumulation of dense antiproton beams, it paved the way for the discovery of the W and Z bosons, which earned Carlo Rubbia and Simon van der Meer the 1984 Nobel Prize in Physics.

The book grew out of lectures given at the CERN Accelerator School, the laboratory’s training programme for accelerator physicists, and it reads that way. The pedagogy is deliberate, building from simplified time-domain models, in which a single particle is followed turn by turn and the corrective kick is derived directly from its measured error, toward progressively more complete descriptions that include the full beam ensemble. There is intentional repetition, which some readers will find slow but newcomers are likely to appreciate, since each pass also tightens the mathematical framework before adding the next layer of complexity.

Of particular interest is the frequency-domain treatment of coasting beams in chapter 4, in which the author constructs the Schottky noise spectrum of an unbunched beam from first principles, starting with the Fourier decomposition of a single circulating particle’s current and building up to the full band structure. The main result, that the integrated power of each Schottky band is constant while its bandwidth grows linearly with harmonic number, is laid out clearly.

Möhl then extends the treatment to transverse signals, showing how the betatron sidebands, the spectral lines associated with the transverse oscillations of the particles, arise naturally, and how their structure encodes machine parameters such as tune and chromaticity. This is especially relevant in practice, since Schottky signals are often the only non-invasive diagnostic available when the beam is unbunched, and most other instruments are blind. The contrast with bunched beams, taken up among the special applications in chapter 8, is also instructive: cooling depends on particles shuffling between samples, the so-called mixing, and correlated synchrotron motion in bunches undermines exactly that, leading to substantially worse cooling rates.

The book fills an important gap as a self-contained reference on stochastic cooling theory and is well worth reading for anyone working in accelerator physics or interested in the topic.

The Standard Model: a practical step-by-step guide

This new textbook offers an intermediate-level presentation of the Standard Model (SM). It assumes that students have a knowledge of relativistic quantum mechanics and are comfortable with the Dirac equation, the properties of Dirac spinors, and covariant notation, including how to write Lagrangians in it. It also assumes familiarity with Feynman diagrams in quantum electrodynamics and with the basic application of the Feynman rules. Even so, the book opens with a substantial revision chapter taking up about a quarter of the main text, covering discrete symmetries, the S-matrix and aspects of QED, with a complete calculation of Compton scattering between a photon and an electron. Although the author does not treat phase-space calculations – the integrals over the kinematics of final-state particles that turn a matrix element into a cross section or decay rate – as an independent topic, the complicated example of muon decay is worked out in detail.

A distinctive feature is the inclusion of fully worked-out examples, in which the algebra is carried out at much greater length than in most other textbooks. The effect is that of a blackboard lecture, rather than one of those slide presentations in which all the so-called “trivial” steps – that students rightly find anything but trivial – are omitted. Several of the examples broaden the physical understanding in ways rarely seen at this level: the hydrogen atom solved with the Dirac equation, coupled oscillators, mechanics problems involving torque, forces and inertia, all pressed into service to illuminate the underlying particle physics.

The Standard Model: A Practical Step-by-Step-Guide — Credit: Cambridge University Press

The heart of the volume is divided into two parts. The first sets out the basic elements of the SM, starting with the electroweak interactions mediated by photons, W and Z bosons, through gauge symmetry, spontaneous symmetry breaking and the Higgs boson, and ending with QCD. The second turns to applications. It includes an accessible treatment of higher-order corrections, flavour physics, flavour-changing currents and the CKM matrix that encodes the mixing between quark generations. It also features a chapter on QCD applications, covering the parton model and deep-inelastic scattering. A more elementary treatment is reserved for hadronisation, the non-perturbative process by which quarks and gluons turn into observable hadrons.

A clean section on the lowest-order calculation of gluon–gluon fusion Higgs-boson production at hadron colliders sits alongside the more standard material. Kaon oscillations, CP violation and neutrino oscillations close the book, alongside a 20-page experimental chapter of the kind one might expect in an introductory course. The book is presumably aimed at students with a stronger grounding in quantum field theory than in particle physics, who are now building from that base toward an understanding of the SM.

Overall, the book is faithful to its title. It sticks to the SM and avoids new-physics scenarios, save perhaps for neutrino oscillations, which some already classify as beyond it. Occasional bridges are built nonetheless. For instance, Majorana neutrinos appear in one of the exercises, while an accessible treatment of the θ-QCD term comes a breath away from discussing axions. The author does not shy away from using modern computational tools, with examples drawing on Mathematica, FeynCalc, the event generators MadGraph and Pythia, which simulate hard scattering and the subsequent parton showers and hadronisation, and the detector-simulation package Delphes. Each chapter ends with a small set of problems.

The result is a clear and engaging treatment, carefully tailored to its readership. Its fresh perspective, its unconventional examples and the painstaking attention to algebraic detail, make it a useful resource not only for students but also for instructors teaching introductory particle physics.

Die urknallmaschine

How to explain CERN to someone who’s never been there? That’s indeed not always easy, but this book can surely help.

The German-language Die Urknallmaschine (The Big Bang Machine) by Barbara Warmbein offers an authentic glimpse into the research at CERN and the unique, sometimes extraordinary, environment in which it happens.

Warmbein has a real talent for combining fundamental ideas in physics and engineering at CERN with illustrative analogies. She creates mental pictures that make complex ideas easier to grasp, and much more likely to stick. The level is accessible to anyone with a general interest in physics and remains engaging without becoming overly technical or intimidating. This makes the book a good choice not only for readers without a CERN background, but also for anyone looking for better ways to explain the laboratory to friends, family or visitors.

Warmbein starts with the big questions, the great mysteries of our universe, and gradually builds a bridge to CERN’s research. Along the way, she explores both what we already understand and what remains unknown, often linking these ideas to everyday experiences. She weaves in historical context, reminding us, for example, that around the year 1900 many physicists believed that their work was almost complete, just before quantum mechanics and special relativity changed everything once again.

After roughly 50 pages dedicated to well-pitched basics, Warmbein moves on to accelerators and detectors, before widening the perspective to CERN as an organisation. She traces its development over the past 70 years, highlighting both what happens on site and the global network of institutes and collaborations that make CERN possible.

A nice touch is the inclusion of small but interesting pieces of side information, details that even people working at CERN might not know, in a compact form. This adds an extra layer of discovery, even for long-time insiders. The applications of accelerators outside fundamental research are one such example. Warmbein presents her material in a warm, approachable way, capturing both the science and the human side of CERN in one stroke.

Physics with dad jokes

For Daniel Whiteson, professor at the University of California, Irvine, and a researcher on the ATLAS experiment at CERN, there was no obvious path ahead. As an undergraduate, he moved between fields, looking for one that fit. One summer, he tried plasma physics and later moved on to one of those laser labs in which, as he argues, “something is always broken”. It was only in particle physics that things eventually clicked. “That’s when I realised it’s possible to have fun doing research,” he recalls. “I also enjoyed the daily work of computer programming and data analysis, not vacuum chambers or optical systems. Particle physics is really personal.”

That idea has stayed with him. “We’re all interested in the big questions, but what you enjoy doing day-to-day determines where you can actually contribute,” he says. Finding that alignment, however, is rarely immediate. “When you’re young, you don’t know yourself well enough to know what you are going to like,” he reflects. “If everybody knew at 20 who they wanted to be at 40, their lives would be much simpler.”

Turning point

A second turning point came during his postdoctoral years, when he considered leaving academia. He had no doubt about the science. What worried him, instead, was the life that came with it. Looking at faculty 10 years older, he saw few who seemed happy, and few who had managed a good work–life balance. Luckily, there were exceptions. “I found mentors who seemed to be having healthy patterns and tried to follow their lead,” he says. “I thought I could make it work.”

Whiteson’s research with ATLAS focuses on “breaking down barriers to discovery, by using machine learning to make previously intractable problems tractable”, an area he has been working in since the late 1990s. One example is the use of machine-learning algorithms to distinguish rare particle signals from overwhelming background noise in LHC data, improving the sensitivity of searches for new physics beyond the Standard Model.

In parallel, he has built a career in science communication. The output spans podcasts, books, such as his recent volume Do Aliens Speak Physics? with cartoonist Andy Warner, and the PBS Kids series Elinor Wonders Why. Rather than teaching facts, the show portrays the process of science: when the children ask questions, adult characters don’t know the answer and show the children how to work it out for themselves.

We’re all interested in the big questions, but what you enjoy doing day-to-day determines where you can actually contribute

That journey started alongside cartoonist Jorge Cham. “I always wanted to use cartoons to convey science, because I feel like our field is so abstract that visuals are really important,” he says. Humour, too, became central to that approach. “I feel like humour is such an important part of communication. It puts people at ease.” As he puts it, “How complicated could this quantum field theory be if there’s dad jokes mixed in, right?”

After Whiteson reached out to Cham, the collaboration grew quickly. The first video, on dark matter, reached more than a million viewers on YouTube. A second, on the Higgs boson, was cited in the further-reading materials accompanying the 2013 Nobel Prize announcement. All the while, research did not halt. “I never stopped having students. I never stopped going to CERN. I never stopped writing papers,” he says. “My scientific productivity never dropped or dimmed.” If anything, communication helped. “I learned physics because I had to describe it for the general public. And that improved my science.”

Still, he is candid about the challenges: “The field is not always supportive of those kinds of efforts away from research.” He has felt this himself. “It’s unfair, but it’s also the reality,” he says. “There’s a tension within the community, and things are changing.”

Compelling prose

If there is one skill Whiteson feels is consistently underestimated, it is writing. “Writing is so important and so undervalued, especially in this AI age.” Papers are a natural example “If you read a paper, and it’s written sloppily, you think maybe the work is sloppy. Whereas if you read a paper, and it’s crisp and clear, then you feel grateful to the author for putting in the time to think things through.” Grants are another, and here the audience matters too. “Most of the grants submitted have great ideas. If the prose is compelling, it captures that bored grant reviewer and convinces them that you know what you’re doing.” The same applies to communication more broadly. “The challenge of science communication is not knowing if you understand the material, it’s whether you understand where the audience is coming from, and how to guide them.”

For early-career researchers, his advice is simple. “Do not get advice from people my age,” he says, pointing to how quickly the field is changing. “There’s now a path for people who do AI and physics. Thirty years ago, there really wasn’t. Even AI was like a side gig for folks like me!” What matters more, in his view, is to be true to oneself. “Do the stuff you find fun,” he says. “Because that’s where you’re going to shine.”

Mark Alastair Rayner 1983–2026

It was with profound shock and sadness that we learned of the passing of Mark Rayner, editor of CERN Courier, on 23 March due to sudden illness. His love of physics, talent for communication and editorial rigour raised the bar for this magazine.

Mark was born in Hounslow, England, on 7 October 1983 and studied physics at Worcester College, University of Oxford, from 2002 to 2006. In 2005 he spent three months at CERN as a Summer Student working on tests of the ATLAS transition-radiation-tracker end caps. He continued at Oxford with a PhD, participating in the Muon Ionisation Cooling Experiment (MICE) based at the Rutherford Appleton Laboratory. His thesis described the development of a novel technique for characterising the MICE muon beam and demonstrating its suitability for a muon cooling measurement, an essential step on the path towards a possible neutrino factory and muon collider.

In 2011, he moved from accelerator physics to neutrino physics, joining the University of Geneva both as a lecturer and as a researcher working on the T2K, Hyper-Kamiokande and BabyMIND experiments. Over the years, Mark supervised several students. In the process he deconstructed the weaknesses in the T2K detector system, realising that an upgrade of the detector setup at the source was necessary for the long-term programme. An upgrade was proposed, with a much simplified and better geometry, largely using detector techniques developed in MICE. It was approved in 2019 and is now successfully operational.

As a physicist, Mark stood out for his care and originality. He liked simplicity and elegance, and to understand the relative causality of correlated observations. He made many important contributions and was happy to do so, without seeking recognition.

A natural educator and communicator, Mark trained as an apprentice physics teacher at Ecole Internationale de Genève in 2018. The following year, he joined CERN as a senior fellow working on the Courier, where he played a major role in the launch of the magazine’s website and rose quickly to become deputy editor. When his fellowship ended, Mark took his exceptional skills to the World Economic Forum, where he managed the production of a portfolio of publications and tools relating to education, skills and learning, and served as lead author for the Future of Jobs report 2023.

Mark returned to CERN as a staff member in 2024, as editor of the Courier. Over a short period, his eye for design, his mastery with words, and his ability to interpret and display complex information in novel ways sharpened the impact of CERN’s flagship publication. He also paid particular attention to improving the visibility of gender diversity in these pages and to developing the magazine’s online presence, enabling him to connect particle physics with new audiences. He took great pride in his work and in engaging with authors to shape their stories. He had huge respect for those who devoted their lives to fundamental research in physics and was widely recognised for his dignity and professionalism among members of the international particle-physics community.

Above all, Mark cared deeply about everything he did, and especially about the well-being of others. His pursuit of excellence and his remarkable attention to detail set a standard that inspired those around him, and this is reflected in the deeply motivated team that he built and nurtured. He was highly cultured, played the flute, and sang in the Geneva Gospel Choir.

Mark was a man of great intellect, warmth and spirit, whose presence brought light to those fortunate enough to know him. He will be remembered with great respect and will be profoundly missed.

Jan Żylicz 1932–2026

On 16 February 2026, the Polish physics community suffered a painful loss – professor Jan Żylicz, an outstanding nuclear physicist, passed away in Warsaw.

Jan Lubart Żylicz was born on 7 January 1932 in Góra, in the Kashubian region, and completed his studies in physics at the University of Warsaw in 1955, under the supervision of Andrzej Sołtan. His work on beta spectroscopy of strongly deformed nuclei, conducted at the Institute of Nuclear Research, contributed to his 1961 PhD at the University of Warsaw. He continued his research on beta decay of rare-earth nuclei during a stay at the Niels Bohr Institute in Copenhagen from 1963 to 1965. One of his important contributions was the identification of the Coriolis effect’s role in rotating atomic nuclei, which served as the basis for his habilitation at the University of Warsaw in 1967.

His research stay at the CERN–ISOLDE facility, from 1970 to 1971, was devoted to the study of nuclides far from beta stability. This topic significantly influenced his subsequent scientific work, and he spent two further research stays in the mass separator group at GSI Darmstadt, from 1978 to 1979 and from 1986 to 1987. The close and long-lasting collaboration with GSI, which Jan initiated, played a crucial role in the scientific development of young scientists in the Warsaw group, many of whom completed postdoctoral fellowships there.

He led several large research projects, including studies of octupole correlations in actinide nuclei. This work was to some extent pioneering and contributed to growing interest in this topic among theorists and experimentalists. He devoted particular attention to exotic nuclides far from the beta-stability line, notably through the extensive research programme on Gamow–Teller transitions in the region of the doubly magic tin isotope ¹⁰⁰Sn, carried out mainly at GSI Darmstadt, but also at the ILL in Grenoble, the University of Jyväskylä and CERN–ISOLDE.

Jan had a talent for initiating valuable research programmes that could be carried out in Poland under the modest experimental conditions available in Warsaw at the end of communism. For example, he developed a new method for measuring the K-shell ionisation by charged particles, which was used for many years at the Warsaw Van de Graaff accelerator and yielded several results of practical importance. He was also interested in phenomena at the interface between nuclear and atomic physics, and proposed a programme to study radiative electron capture in forbidden transitions. Among Jan’s most original achievements are his works on the isomeric state of ²²⁹Th, and the idea of spin-mixing oscillations in the states of the hydrogen-like ion ²²⁹Th⁸⁹⁺. This work was ahead of its time – attempts to confirm the phenomena he predicted are currently underway at the ESR storage ring at GSI Darmstadt.

Associated with the University of Warsaw from 1972 to the end of his career, Jan established a new Nuclear Spectroscopy Group, which he headed until 1994, and served as director of the Institute of Experimental Physics from 1994 to 2002. In 2005, the Polish Physical Society awarded him its highest distinction – the Marian Smoluchowski Medal – and the European Physical Society honoured him with the title of EPS Fellow. He was also awarded the Knight’s Cross of the Order of Polonia Restituta.

Jan was an outstanding educator, whose lectures were valued for their clarity and for the passion with which he explained the essence of a problem. He attached particular importance to mentoring young academic staff, supporting and patiently motivating them. He sent them to international conferences and helped to organise research stays at leading Western institutions, which was especially important at a time when this was not as easy as it is today. He supervised 17 master’s theses and 12 doctoral dissertations, with six of his students later becoming professors of physics. Their successes brought him joy and pride, and he considered creating the conditions for the scientific development of his younger colleagues his principal achievement.

Jan Żylicz was a warm and kind man with an extraordinary sense of humour. Working with him gave us a sense of purpose, satisfaction and joy. He will forever be remembered as a model scholar and teacher.

Roger Barlow 1951–2026

Roger Barlow passed away suddenly on 1 February 2026 at his home in Wales. Roger had an illustrious career in particle physics and, latterly, also in accelerator physics. He was well known internationally for his work in statistics, in particular for his widely used textbook, Statistics: A Guide to the Use of Statistical Methods in the Physical Sciences, published in 1989.

Roger was born on 14 April 1951 in Canterbury. After attending Edinburgh Academy, he obtained a place to study for his first degree at Oxford. He then went to Cambridge, where he completed his PhD in 1977 on proton–deuteron interactions at CERN’s 2 metre bubble chamber. Roger then took up a research post at Oxford, working on the TASSO experiment, and contributed to the discovery of the gluon in 1979.

In 1980, Roger was appointed to a lectureship at the University of Manchester and joined the JADE Collaboration, where his work on event reconstruction and Monte Carlo simulation led to one of the early measurements of the B-meson lifetime. During his early years at Manchester, Roger moved on to the OPAL experiment, becoming leader of the Manchester team in 1991. On OPAL, he helped design, build, commission and operate the muon chambers, which were crucial for many Standard Model physics studies, including precision measurements of the Z boson.

Roger became the overall leader of the Manchester particle-physics group in 2005, after the retirement of Robin Marshall. The group was then also involved in ATLAS, D0, several neutrino experiments and BaBar, which Roger had joined. Under his leadership, the particle-physics group grew to more than 100 members. As a collaborator on BaBar, he helped design the electromagnetic endcap, and he supervised the construction of half of the detector in Manchester. His data analyses included setting new limits on the existence of second-class weak currents in tau–lepton decays. As BaBar wound down, he took his group into LHCb.

In the early 2000s, Roger began researching accelerator science, forming an accelerators group in Manchester and becoming a founding member of the Cockcroft Institute of Accelerator Science and Technology. He was principal investigator for the CONFORM project that led to the successful operation of EMMA, the world’s first non-scaling FFAG accelerator. This provided a proof of principle for a new type of accelerator with many potential applications. In 2011, he left Manchester for a post at the University of Huddersfield, where he formed another accelerator-science group.

In addition to his textbook, Roger produced several influential works on statistics, including a description of extended maximum likelihood, a highly cited paper on fitting using finite Monte Carlo samples, and a detailed paper on the treatment of systematic uncertainties.

Roger was a dedicated and skilled teacher, who cared deeply about educating the next generations. Among his many contributions to the public understanding of science, he introduced the Particle Physics Masterclasses for high-school students, which quickly expanded across the UK, before becoming truly international. In recognition of this, he was awarded the Institute of Physics’ Lise Meitner Medal and Prize in 2022.

Roger retired from Huddersfield in 2017, but continued to work on BaBar and LHCb, and to publish papers and lecture on statistics, right up until his passing.

Outside of physics, Roger was active in UK national politics as a member of the Liberal Democrats. He was selected three times to stand as a candidate for the UK parliament. He will be greatly missed by his wife, Ann, his children Edward and Eleanor, his extended family, and his many friends and colleagues across the world.

Michael Wohlmuther 1975–2025

Michael Wohlmuther, an internationally recognised expert on spallation physics and technologies, tragically passed away on 30 October 2025 in Lund, Sweden, at the age of 50.

Michael was born on 26 January 1975 in Bruck an der Mur, Austria. In 2003, he received his PhD from the Graz University of Technology for his thesis “An Intranuclear Cascade Event Generator”, written in collaboration with Forschungszentrum Jülich.

In his different roles, Michael contributed greatly to the development of targetry technologies, both from the physics and the engineering perspective. One of his major contributions was serving as project leader for the MEGAPIE project at PSI, the world’s first high-power liquid-metal spallation neutron source. More recently, he actively participated in the effort to develop the ESS high-power tungsten target and related material analyses.

His involvement extended beyond PSI and ESS, and included collaborations with CERN, the Facility for Rare Isotope Beams (FRIB) and Oak Ridge National Laboratory (ORNL). He influenced the global landscape of spallation, high-energy physics and radioactive-ion-beam target technologies, in both operational practice and post-irradiation analysis.

Michael’s work consistently achieved international recognition, and he served on important review panels and advisory committees, including the High-Power Targetry Workshop Scientific Program Committee and the FRIB Target Advisory Committee. He was also a founding member of CERN’s HiRadMat Scientific Board.

Michael was an invaluable member of the spallation targetry community for many years. He contributed to our shared endeavours with his vast expertise, his attention to detail and his kindness towards the people around him. He will be remembered for his warm and welcoming spirit, his readiness to greet everyone with a smile, and his genuine humility.

Our thoughts and sincerest condolences are with Michael’s family, his friends and all those who were fortunate enough to have known him. He will be deeply missed by everyone who had the privilege of working alongside him.

Superconductors for the energy frontier

Fill hundreds of copper tubes with a powder of niobium and tin, and then stack them in the form of a cylinder. Draw this out into a composite wire hundreds of kilometres long and barely a millimetre in diameter. Braid it into a rectangular cable and insulate it in fibreglass. Wind it into coils, bake for a week at precisely 650 °C and impregnate with resin. Assemble them with sub-millimetre precision under a compressive stress of one tonne per square centimetre, cool the magnet to a few kelvin and power it with tens of thousands of amps. This is not alchemy. This is a possible recipe for a Nb₃Sn magnet.

Whether made of Nb₃Sn or higher-performance superconductors, such devices promise to substantially improve the discovery potential of hadron colliders. Since their energy reach scales as the dipole field times the size of the tunnel, each additional tesla directly expands the energy frontier.

What makes these magnets unique is their compactness. Superconducting coils can carry a current density of order 500 A/mm², a factor 100 higher than what can be tolerated by copper with active cooling. A magnet based on superconductivity can therefore have coils that are narrower and lighter.

No application of superconductivity pushes this limit harder than an accelerator magnet. Larger coils mean larger magnets and an unaffordably large tunnel to accommodate them. Accelerator magnets must therefore be highly optimised in space and cost – the capsule hotels of superconductivity – and this extreme optimisation creates opportunities for spinoff applications, from lightweight motors for electric aircraft to power transmission beneath the pavement of a crowded metropolis. Superconducting accelerator devices have already paved the way for societal applications in medical imaging and advanced accelerators for cancer therapy, and the field continues to benefit from strong research synergies with fusion tokamaks, though their toroidal coils don’t need to push the limits of current densities in the same way.

Superconductors also save energy. At the LHC, more than a thousand niobium–titanium alloy (Nb–Ti) superconducting dipoles are powered by only 40 MW. This is much less than what is consumed by the LHC’s injectors.

As dipoles based on Nb-Ti superconductors are limited to a maximum achievable field of nearly 10 tesla, corresponding to an operational field of about 8 tesla with acceptable margins, accelerator physicists and engineers are exploring the use of better superconductors to roughly double their field. The options include Nb₃Sn, which will soon be used in an accelerator for the first time at the HL-LHC, and “high temperature” superconductors that promise much higher performance and a simplified accelerator infrastructure. But dipoles are much more difficult to design than solenoids. Though 30 tesla solenoid magnets are already available on the market, no one has yet succeeded in building a 20 tesla dipole magnet.

Shear complexity

An accelerator dipole poses several challenges compared to a solenoid. While a solenoid’s current loops generate an axial magnetic field, a dipole must use vertically separated coils to generate a vertical magnetic field; for the same total coil thickness and current density, a solenoid can provide twice the field strength of a dipole; and the field distribution and the forces exerted on the coils are much more difficult to control. In a solenoid, electromagnetic forces are perpendicular to the conductor, but in a dipole they push the coil towards the midplane and outwards, with a two-dimensional distribution that includes shear stresses.

**Superconductors for high-field accelerator magnets** Constant temperature (4.2 K unless specified) slices of the “critical surface” of several superconductors. Superconductivity is lost for higher values of current density and surface magnetic field, and a balance must be struck between compactness (high current density) and field strength. Credit: A Ballarino

The engineering challenge is increased by the need for dipoles to operate precisely during the ramp, when particles gain energy with every turn after being injected into the collider, requiring increasingly strong magnetic fields to bend them. To ensure that accelerator physicists can make tightly focused beams collide with high luminosity inside the experiments, the field must be uniform to better than one part in 10⁴ across two thirds of a dipole’s aperture as the field increases up to a factor 15. These challenges are not present in either medical-imaging magnets or the toroidal coils used for fusion, which must operate at a constant current, though the toroidal coils used for fusion are subject to rapidly varying external magnetic fields.

In the context of the 2026 update to the European Strategy for Particle Physics (ESPP), advanced high-field dipole magnets would be needed by the hadron-collider phase of the Future Circular Collider (FCC-hh) and the proposed muon collider. Due to its exceptionally large and unstable beams, a muon collider would also require a kilometre-long channel of superconducting solenoids with alternating gradient, and a final superconducting cooling solenoid with a strength of roughly 40 tesla before the collider ring. These challenges are complementary to what is required by the FCC-hh, and the community is devoting significant research and development in this direction.

The targets initially set for the FCC-hh in 2014 were based on round numbers: a 100 km tunnel and a centre-of-mass energy of 100 TeV. This required 16 tesla dipoles, one or two tesla above what can be done with adequate margins and costs with present technology. After a decade of studies, the tunnel size was reduced to 91 km to fit geological constraints, and the field was brought down to 14 tesla, allowing a centre-of-mass energy of 85 TeV after some optimisation of the lattice. This 15% reduction in the energy in the centre-of-mass frame has had a major effect on the energy consumption of the collider, as synchrotron radiation reduced by 50%. A similar tuning occurred for the LHC, which was initially imagined at 16 TeV with 10 tesla magnets rather than today’s 13.6 TeV and 8.1 tesla.

The baseline design for the FCC-hh dipole magnets is Nb₃Sn technology operated at 1.9 K, though the ESPP documents also note three other possibilities: hybrid magnets that use substitute Nb–Ti for Nb₃Sn in the lower field regions; operation at 4.5 K; and a high-temperature-superconductor option operating between 4.5 and 20 K with magnetic fields in the range 14 to 20 tesla.

The Nb₃Sn path

Nb₃Sn was discovered a few years before Nb-Ti and has the advantage of providing current densities in excess of 500 A/mm² up to 16 T (see “Superconductors for high-field accelerator magnets” figure). After 35 years of research, fields have now reached 14.5 tesla, close to the 15–16 tesla target needed to have magnets operating at 14 tesla in the FCC-hh with adequate margins (see “Niobium dipoles” figure). The main goal today is to produce a double-aperture short-model Nb₃Sn magnet with all features specified in the FCC-hh design. This should be achieved by 2030 and then scaled up in length.

**Niobium dipoles** The evolution of the achieved field in Nb-Ti and Nb₃Sn dipoles. Credit: E Todesco

A key challenge is to reduce the quantity of Nb₃Sn, thereby lowering both the cost and hysteresis losses during field ramping. As the magnetic field changes, currents are induced within the superconducting filaments, leading to energy dissipation that must be carefully controlled. Minimising these losses is one reason for the complex, multi-filamentary architecture of superconducting wires. The smaller filaments of Nb-Ti can significantly reduce the losses, and Nb-Ti costs five to 10 times less than Nb₃Sn.

A second engineering challenge is to achieve a mechanical structure capable of keeping the coil in compression during powering but not overstressing it. The stress limits of Nb₃Sn are of the order of 200 MPa, and the required precompression for a 14 tesla dipole is about 150 MPa.

Another challenge of the low-temperature path would be logistical: the production of roughly 5000 tonnes of Nb₃Sn. This corresponds to a 1 kA cable from the Earth to the Moon at a cost of several billions of dollars. These numbers are an order of magnitude larger than what was needed for the Nb-Ti coils of the LHC.

Despite these challenges, Nb₃Sn technology is now well established for small series, and will soon play a key role at the High-Luminosity LHC – the technology’s first use in a working accelerator, though for focusing beams rather than bending them (see “Nb₃Sn quadrupoles” figure). But newer superconductors may well prove competitive.

The high-temperature path

In 1986, Johannes Georg Bednorz and Karl Alexander Müller announced the discovery of superconductivity above 35 K, something not foreseen by theory, and well above the boiling point of liquid helium. “High-temperature” superconductors (HTS) not only remain superconducting at high temperatures, in many cases above the boiling point of liquid nitrogen (though at 77 K HTS performance is not yet adequate for our needs ), but also at high fields. HTS solenoids have been constructed with fields up to 40 tesla, and though the problem of degradation is not yet totally solved, progress has been outstanding.

Three families of superconducting conductors are currently available or emerging on the market: rare-earth barium copper oxides (REBCO), bismuth strontium calcium copper oxides (BSCCO) and iron-based superconductors (IBS).

Nb3Sn quadrupoles — **Nb₃Sn quadrupoles** The cross section of one of the new final-focus quadrupoles for the High-Luminosity LHC. Operating at peak fields of up to 11.5 tesla, the quadrupoles will provide significantly stronger focusing and larger apertures than the Nb-Ti magnets used in the LHC, enabling tighter beam squeezing and higher collision rates. When the upgraded collider comes online in 2030, these quadrupoles will become the first Nb₃Sn magnets to be used in a working accelerator. Credit: OPEN-PHO-ACCEL-2017-010-2

REBCO is of strong interest in the world of fusion. Billions of dollars of investment have reduced the cost by more than an order of magnitude in the past decades. REBCO comes in tapes (see “Frontier superconductors” figure). A 12 mm-wide tape has thickness of 0.1 mm and can carry 1500 A at 4.5 K, or about half that at 20 K. 20 tesla peak field coils have been built and tested for fusion applications, and private investors plan to build reactors that are much more compact than ITER, which is based on Nb₃Sn technology.

Manufacturing REBCO coils is greatly simplified compared to Nb₃Sn as the tape needs no temperature treatment; but the technology used to wind the tapes is not easy to adapt for accelerator dipole magnets, which are radically different from the toroidal coils designed for tokamaks. The challenge here is not to develop a conductor for accelerator magnets, but to adapt our magnet designs to this amazing tape. There is a long way to the 15–16 tesla target, but the potential is huge, with progress being made in Europe, the US and China (see “HTS dipoles” figure).

**HTS dipoles** The evolution of the achieved field in HTS dipoles. Credit: E Todesco

And what of the other HTS superconductors? BSCCO has the great advantage of round wires, but must be treated at 800 °C and it does not profit from synergies with fusion. At present, this path is only being pursued in the US, with achieved fields of just 1.8 T. IBS is being actively developed in China and Europe, but its current density has not yet matched the performance of REBCO, and the best results were obtained for tapes rather than wires.

HTS would allow operation at 20 K, with a simplification of the cooling scheme and a possible reduction in the energy consumption of the collider, though at 85 TeV half of the heat loads are due to synchrotron radiation, which does not depend on the operational temperature of the magnets. Moreover, REBCO tape has a single filament, as wide as the tape, and therefore the saving from the higher operational temperature could be compensated by larger heat losses. Estimating the energy balance is far from trivial: do not draw easy conclusions!

Optimal solution

Addressing these challenges is the work of the High Field Magnet (HFM) programme, an international collaboration with 15 institutes steered by CERN that was founded in 2021. HFM is exploring multiple different designs to find the optimal solution, from the most classical to the more exotic, and novel ideas should be explored in parallel to the most conservative paths. Though there are major challenges ahead, solving them promises societal benefits via a number of diverse spinoff applications.

High-field magnets remain one of the hardest problems in applied superconductivity. The next decade will be decisive for understanding the feasibility and cost of the FCC-hh.

Execution mode

Going all the way back to Robert Wilson in the 1960s, some formidable figures precede you as Fermilab director…

Coming back to Fermilab is, for me, a little like coming home. My family and I moved to the United States in 1998, and Fermilab was the first place I worked in the Department of Energy (DOE) system. It was also a place where people really took me in. Fermilab, like many national laboratories, is built on the shoulders of giants – and Robert Wilson was one of them.

He got this huge site, more than 6000 acres, with a real vision for expansion and growth in science. He was also a genuine fan of architecture, truly inspired by it. Our Wilson Hall is a tribute to that. It echoes what people call the folding hands of Beauvais Cathedral in France. Having that building stand out from the prairie was a statement.

That’s Robert Wilson’s legacy at Fermilab: a science of statements and the ability to do things fast, effectively, things that people thought could not be done. So, honestly, sitting in that chair feels good.

Wilson’s 1969 Congressional testimony is one of the most celebrated defences of fundamental science. What do you make of his case today?

He told Congress that high-energy physics had to do with dignity and all the things that we really venerate and honour in our country. That is still true. Despite the strain on science funding and all the questions about whether we are spending money effectively, the government is still willing to invest more than five billion dollars at Fermilab over the next five to ten years. This feels almost contrarian to what you hear in the press. Yes, science is under pressure. But the commitment is there, for the very same reason Bob Wilson stated back then.

That said, I believe we carry a genuine responsibility to deliver to society. That has been the basis of the social contract since Vannevar Bush wrote Science, the Endless Frontier in 1945; the document that helped create the national laboratory system and agencies such as DOE, the National Science Foundation and NASA. I don’t expect every citizen to understand exactly what a neutrino does or why it matters. But the outcomes of science, and the technology we develop on the way, whether that’s AI, quantum information tools, electronics, those are things we have to deliver. It’s part of the social contract.

Then, under Leon Lederman, and driven forwards by figures like Helen Edwards, Fermilab expanded the world’s energy frontier with the Tevatron…

Helen Edwards is actually directly responsible for the fact that I’m in this country. It’s her fault, really. When I was a group leader at DESY in 1998, 37 years old, with two small kids and having just built a house in Germany, Helen walked into my office. She asked, “Norbert, what do you want to do with your future?” She was very direct and wouldn’t take no for an answer. I hesitated, and she said, “You need to think about this. You should go to the United States.” Six months later, I was at Fermilab.

She was undeterrable. If she had a mission, a North Star, there was no lab director, no government official, no one who could deflect her from it. She and Alvin Tollestrup, a name that doesn’t get talked about enough, developed the superconducting magnet technology under Leon Lederman’s leadership that made the Tevatron what it was. That technology later allowed DESY to build HERA and ultimately landed in the LHC at CERN.

Alvin could explain superconductor physics on first principles and very quickly come to how you wind a magnet and what fundamentally limits its performance. A physicist and a technologist at the same time. They were both giants. There’s no question about it.

You mentioned moving from Europe to the United States. How different were the two scientific cultures, in the late 1990s?

You sure you want to write about this? [chuckles] Before I left DESY, I went to the director, Björn Wiik. He was himself a visionary leader, the person behind the TESLA concept for superconducting RF. When he asked where I saw myself in five or ten years, I answered, “I want your job. I want to be a director.” He was very direct too. “You are only 35 years old,” he said. “To become a director in Europe, you have to look like me. You have to have grey hair and a beard.” I found that frustrating. But I think it was largely true at the time.

In the United States, age didn’t matter. Nationality didn’t matter. What mattered was: could I do it? A 39-year-old German, alongside a Canadian, Thom Mason, and the son of Croatian immigrants, Anthony Chargin, suddenly found themselves in charge of building one of the biggest science projects in the United States: the Spallation Neutron Source, inspired by a former South Korean accelerator physicist, Yanglai Cho. That’s a story you can’t make up. That is where my career really started.

The transition from Lederman to John Peoples coincided with both the golden age of the Tevatron and the era of the Superconducting Super Collider (SSC). What do those two directors, and that moment, tell us about leadership in big science?

I knew Leon well because I actually lived in his house. He had a place off-site, and when my family first arrived we had very little money, so he said: “You need a house. I have one.” And we moved in. He came by regularly, stored his Porsche in the garage, and we talked a great deal. I learned a lot from him.

He was the kind of person you simply liked. Everybody at Fermilab loved Leon. He was funny, extraordinarily smart and he had a vision for the laboratory. I asked him once why he stepped down after nine years as director. He told me, “If you are a lab director, you have to make important decisions, and with every decision you make, you lose 10 percent of your friends. After 10 decisions, they are all gone. That is when you step down.” That was a true Leon answer. But it reflected his deep understanding of what leadership really costs.

I deeply believe high-energy physics can again be a launchpad for open international collaboration

John Peoples was very different. He was hands-on, deeply involved in building the complex and the Antiproton Source. Where Leon was the beloved visionary, John was the builder who wanted to be involved. And he had two extraordinarily difficult jobs at the same time: managing the closure of the SSC in Texas, which you could see drain him, and running a programme that ultimately delivered the discovery of the top quark.

These were very different people, very different characters. I think every character has its time. That is as true at Fermilab as it is at CERN. You can tell the same story through CERN’s directors. We just lost one, Herwig Schopper, who was a phenomenal leader. He spoke openly about the sacrifices he and the laboratory had to make to get CERN going. And when you look at CERN 50 years later, that is still a defining legacy, with the 27-kilometre tunnel and the science that continues to come out of it.

What lessons does the abandonment of the SSC hold for the large-scale projects being discussed today?

The real lesson of the SSC isn’t the failure itself. It is about implementation. The days when you could go to a government and say your project costs this much, then come back the next year and ask for 20 percent more, and the year after that another 20 percent – those days are gone. That is not the world we live in, and at the scale of projects we are talking about today, it would not be responsible.

John understood that deeply. I have tried to carry it through my own career. On my watch, I will always be direct with our funding agencies about what I see as risks and what things actually cost. That is non-negotiable for me.

Fermilab then repositioned itself at the intensity frontier. How do you keep the laboratory aligned behind the Long-Baseline Neutrino Facility (LBNF) and the DUNE experiment?

You form a team, you focus the team and you execute. That sounds pretty mundane and simple. It is not. It is really hard. CERN went through something very similar under Robert Aymar with the LHC: the necessity to focus every resource and every engineering capability on one thing to make it happen.

I am a scientist, but also a project guy. I wake up every morning thinking about those five billion dollars. That is roughly eight hundred million a year. Three million dollars a day. My job is to organise a team that can responsibly and effectively deploy that every single day to build LBNF/DUNE.

When I spoke at my first all-hands meeting here, I laid out three bullet points, because nobody remembers more than three. First: beam at the DUNE far detector by 2031. Second: science at the High-Luminosity LHC and delivering on our commitments there. Third: develop science, technology and innovation for the benefit of society. Those are the three and everything flows from them.

I use the story of JFK visiting NASA and asking the janitor why he is there. The janitor says: “To put a man on the Moon.” That is the answer I want from everyone here. So I go around and ask people why they are here. And if I don’t get the answer I want, I ask again.

Neutrino physics is also receiving major investments in China and Japan, with JUNO already closing in on the neutrino mass hierarchy and Hyper-Kamiokande equipped to measure leptonic CP violation when it comes online. How does DUNE fit in that landscape?

We live in a world that is not the world of 20 or 30 years ago. We have to recognise that. But I deeply believe high-energy physics can again be a launchpad for open international collaboration.

The neutrino story is phenomenal for the US with the DOE’s support of the DUNE project. It is also great for CERN. The most significant large-scale investment CERN has made in an external experiment is in DUNE. And it goes both ways: Fermilab contributes significantly to the HL-LHC programme. That is one of the healthiest collaborations in the field, both at the personal level and at the level of laboratories and programmes.

In my world, it is better to make the wrong decision and correct it than to make no decision at all

As for competition among neutrino facilities, it’s healthy. It is all about what I call the three C’s: collaboration, cooperation, competition. Every scientific relationship works better when you are clear about which is which. There is competition with other neutrino experiments, of course, in the sense that whoever reaches an answer first gets the golden nugget. But there is also technology exchange, open science and the free sharing of knowledge. Both things are true.

When you look at the DUNE detector and the beam we are building, it will be, hopefully sooner than later, the most effective research instrument for this kind of science. It is nice to be number one. You never stay number one forever, but it is nice. CERN is number one in collider physics right now – a pretty good feeling. But you also have to deliver results.

How would you describe Fermilab’s culture right now?

Scientists are driven by curiosity. That hasn’t changed and it won’t. But when a large institution commits to building a major instrument, there is real tension between the broad research culture that develops over time and the laser focus that construction demands. Is there stress in the system? Yes, honestly, there is. The best thing you can do is recognise that, talk about it openly and make sure people can see the light at the end of the tunnel.

The people who love construction have a clear finish line. The researchers have an extraordinary instrument coming, and the conceptual and technical work they do now is their investment in what comes after. The two groups are not perpendicular to each other. A good instrument requires constant feedback from the science side on what it actually needs to deliver, but you also can’t have an infinite conversation about what to build while you are trying to finish building it. Finding that line is delicate, and I spent my life basically walking it. At the SNS, at LCLS-II, at ITER. You pick.

There is a saying I keep coming back to: culture eats strategy for breakfast. Getting the culture right will take time and requires healthy tension. But it also requires the willingness to make decisions. I am not afraid to make a decision. Sometimes the wrong one, and that’s fine, it needs to be corrected. But in my world, it is better to make the wrong decision and correct it than to make no decision at all.

Where should Fermilab position itself in the next chapter of global high-energy physics?

I wanna stretch my hand to Europe, and to CERN in particular. I am very proud of the connection between our two institutions, at the programmatic level and at the personal level. I think we need to continue discussing how to keep the world open for those that want to share our values and share our way of doing science. People like me should be able to come to the United States. People from here should be able to go to CERN. That’s the foundation of everything we do.

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