Jon Peter Berge 1935–2017 •  Daniel Boussard 1937–2018 •  Violette Brisson 1934–2018

Jon Peter Berge 1935–2017

Jon Peter Berge, known as Peter to his friends and family, passed away on 14 November. He was born in Madison, Wisconsin, to Norwegian immigrant parents and his early years were marked by the Great Depression and World War II, which forced his family to move frequently. He went on to attend the University of California, Berkeley, where he obtained his BA in physics (1956), MA (1958) and his PhD (1964).

At Berkeley, he joined the group under Nobel Prize winner Luis Alvarez at the Lawrence Radiation Laboratory, where he participated on the development of the bubble chamber. While working there, he met his future wife, Louise Holstein. In 1967, Peter obtained a postdoctoral award to work with John Mulvey in Oxford, and three years later he accepted a position at CERN.

In 1974 he took up a permanent position at Fermilab, where he worked on the CDF experiment. He was highly regarded for his skill in writing software used to control high-energy physics experiments, including that which led to the discovery of the top quark in 1995. He remained at the lab until his retirement in 2000.

Peter was an active fencer and competed in tournaments until the mid-1970s. He appreciated chess, good wine, fine dining, classical music and history. He was an astounding writer of endless postcards, including (post-office permitting) beer coasters. He had many lifelong friends and was known as a generous host.

• His friends and colleagues.

Daniel Boussard 1937–2018

The world of radio-frequency (RF) technology lost an outstanding inventor and leader when Daniel Boussard passed away on 6 January. Daniel made vast contributions to the design of RF systems for accelerating and controlling particle beams. He furthered our understanding in particle-beam dynamics and in the intricacies of controlling high-intensity beams. He was a technical innovator across low- and high-power electronics, right through to the sophisticated RF cavities required in the accelerators.

Daniel started at CERN in the late 1960s, working on the PS machine, but was soon recruited to design the beam control systems for the then new SPS accelerator. He made observations of the microwave signals disrupting the beams, putting forward his famous criterion for avoiding them. This started a programme that continues at CERN to this day to understand and control parasitic impedances, which drive beam instabilities, and to invent methods to counteract their effect. With increasing intensity in the SPS, formerly unobserved beam instabilities raised their heads. To deal with this, Daniel pioneered the use of new digital electronics, incorporating them in the one-turn feedback system that he invented to subdue the instabilities.

In the SPS, thoughts quickly turned towards using the machine for the P-PBAR project. Here the problem was to understand and control the noise sources inherent in the RF systems, which destroyed the circulating beams. Pinpointing the critical elements and finding solutions increased the lifetime of the beams from minutes to hundreds of hours.

To accelerate leptons in the SPS for the new LEP accelerator required high RF voltages. Daniel dared to consider installing, for the first time, a superconducting cavity into an environment with high-intensity proton beams. While helping to accelerate the leptons to higher LEP injection energies, it was essential to make this cavity “invisible” to the high-intensity proton beams. He solved this by using sophisticated RF feedback techniques, and the SPS subsequently happily “multi-cycled” protons and leptons for the lifetime of LEP. In these areas, Daniel became an acknowledged leader in the world and his ideas are essential to all modern machines.

With his extensive knowledge of superconducting (SC) RF systems, Daniel was asked to lead the project to install the huge SC RF cavities required for the LEP energy upgrade. While the cavities themselves had to be technically robust, careful design of the electronics to control the voltage and cope with unexpected problems (such as ponderomotive oscillation instabilities) was essential. The experience and understanding gained from SC RF systems in the SPS and in LEP led to their selection for the LHC, and Daniel led the design and implementation of these highly successful accelerating elements.

The tutorials and lectures given by Daniel at CERN accelerator schools on beam loading, RF noise and Schottky diagnostics have become classical references, continuing to serve generations of scientists all over the world. He mastered the art of explaining complex issues in a simple manner.

As a leader, Daniel was kind, fair and highly esteemed, giving clear and carefully thought-out decisions. The remarkable person he was, he took good care of the people entrusted to him and gave honest credit to all those working with him. His natural authority derived from his human qualities and his undoubted technical expertise.

He greatly loved the mountains, going on long hikes both on foot and on skis. It is not surprising, knowing his CERN career, that in his retirement in the south of France Daniel built a guided solar-panel array and became mayor of his village, Valavoire.

• His friends and colleagues.

Violette Brisson 1934–2018

Violette Brisson, a highly respected member of the French particle-physics community who played a leading role in the discovery of neutral currents, passed away on 18 February at the age of 83. She led her long career at the Laboratoire Leprince-Ringuet (LLR) at École polytechnique, and the Laboratoire de l’Accélérateur Linéaire (LAL) in Orsay.

Violette joined the LLR in 1954 as a pioneering young woman in a domain then strongly dominated by male physicists. After a PhD devoted to measurements with cosmic rays, she was invited to work on the first hydrogen bubble-chamber experiment at Brookhaven’s Alternating Gradient Synchrotron. On her return to France, she joined André Lagarrigue’s heavy-liquid detector group. The highlight of the mid-1960s was the design and construction of Gargamelle, a giant bubble chamber to be located on the CERN PS neutrino and antineutrino beams. Violette’s expertise from the US was a strong asset to the project. She took part in the design of the illumination system of the chamber and was responsible for the implementation at LLR of the special scanning and measurement devices needed to handle Gargamelle pictures. Her parallel participation in the stopped-kaon experiment X2 allowed her group to master modern computing techniques for photo analysis.

When Gargamelle started operation in 1971, the focus turned to the search for weak neutral current (NC) events predicted by the Glashow–Weinberg–Salam model. Violette played a leading role in the analysis of the leptonic channel, which turned out to be decisive: a single and by now famous leptonic event with negligible background, together with hadronic events, were the basis of the ground-breaking NC discovery published in 1973. (This saga and the associated controversy with the US competition were related with humour by Violette during CERN’s 50th anniversary celebrations.) Afterwards, she became interested in nucleon structure functions in several experiments with Gargamelle and the Big European Bubble Chamber.

In the early 1980s, when the electron–proton collider HERA entered the scene, Violette fully engaged with this new project. She played a major role in the French contribution to HERA and to one of its experiments, H1. She joined LAL in 1988 and was personally strongly involved in the construction of the H1 liquid-argon calorimeter, going into every detail of its design and not hesitating to spend months within the cryostat to install the complex cabling with the technical teams. Later on she worked on the HERA Fabry-Pérot polarimeter for the high-luminosity phase. HERA did not find the hoped-for quark substructures or leptoquarks, but delivered a wealth of textbook results that provides reference proton-structure measurements for the LHC and, together with LEP and the Tevatron, fully unveiled the mechanism of electroweak unification first hinted at by the Gargamelle discovery of neutral currents.

In the 1990s, though already well advanced in her career, Violette was bold enough to move to a completely new domain – the quest for gravitational waves – within the French–Italian VIRGO experiment.

She again took on a major technical component of the detector, the 3 km-long vacuum chambers of the interferometer arms, taking care of the design of the complex ultra-high-vacuum system. This was a key ingredient to the success. It is comforting that, after many years of constant improvements of the interferometer, Violette was able to experience the first detection of a gravitational wave by VIRGO.

Beyond her talents as physicist, Violette had a deep sense of responsibility and outstanding organisational skills. She took on many collective duties, including assistant management of LLR for many years, the secretariat of the physics committee of the French Science Academy, French representation in international organisations such as IUPAP, and participation on conference committees. In 2003 she was nominated Chevalier de la Légion d’honneur.

Violette was not only a physicist: she was also a spouse, a mother and a faithful friend of many around the world, including a lot of colleagues. She led her life with passion, with a long and dense career crowned by two major discoveries. She will remain an inspiring model for all of us, and in particular to young female physicists.

• Her friends and colleagues.

About the author

• Jon Peter Berge 1935–2017 • Daniel Boussard 1937–2018 • Violette Brisson 1934–2018