Frank Tecker, Hermann Schmickler and Christine Vollinger take a look at the history, impact and future of the CERN Accelerator School.
Forty years ago, the accelerator world looked quite different to what it is now. With the web yet to be invented, communication relied on telephones and written texts received via faxes or letters. Available information existed in the form of published books, conference proceedings or scripts from university lectures. Accelerator-physics models were essentially based on approximate solutions of differential equations, or on even simpler linearisation of the problem at hand. Technologies relied on experience from accelerators that had previously worked well, with new concepts tested after sometimes cumbersome calculations and usually by building prototypes. Completely new accelerator technologies such as superconducting magnets required the construction of full-size accelerators (such as the Tevatron at Fermilab) to learn, often painfully, about the phenomenon and impact of persistent current decays.
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!
