Obituaries

Yong Ho Chin 1958–2019 • Albert Hofmann 1933–2018 • Vladimir Rittenberg 1934–2018 • Pio Picchi 1942–2019

Yong Ho Chin 1958–2019

A foremost accelerator physicist

Yong Ho Chin

Yong Ho Chin, a leading theoretical accelerator physicist at the High Energy Accelerator Research Organization (KEK) in Japan and chair of the beam dynamics panel of the International Committee for Future Accelerators (ICFA) since November 2016, unexpectedly passed away on 8 January.

In 1984, Yong Ho received his PhD in accelerator physics from the University of Tokyo for studies performed at KEK under the supervision of Masatoshi Koshiba, who won the Nobel Prize in Physics jointly with Raymond Davis Jr and Riccardo Giacconi in 2002. Yong Ho participated in the design and commissioning of the TRISTAN accelerator, and later in the designs of the KEKB and J-PARC accelerators, along with major contributions to JLC (the Japan Linear Collider) and ILC (the International Linear Collider). In the 1980s and 1990s he spent several years abroad, at DESY and CERN in Europe, and at LBL (now LBNL) in the US.

In his long and distinguished career, Yong Ho made numerous essential contributions in the fields of beam-coupling impedances, coherent beam instabilities, radio-frequency klystron development, space–charge and beam–beam collective effects. He considered his “renormalisation theory for the beam–beam interaction”, developed during his last six months at DESY in the 1980s, as his greatest achievement. However, in the accelerator community, Yong Ho Chin’s name is linked, in particular, to two computer codes he wrote and maintained, and which have been widely used over the past decades.

The first of these codes, developed by Yong Ho in the 1980s, is MOSES (MOde-coupling Single bunch instabilities in an Electron Storage ring), which computes the complex transverse coherent betatron tune shifts as a function of the beam current for a bunch interacting with a resonator impedance. The second well-known code, written by Yong Ho in the 1990s, is the ABCI (Azimuthal Beam Cavity Interaction) code for impedance and wakefield calculations. This served as a time-domain solver of electromagnetic fields when a bunched beam with arbitrary charge distribution goes through an axisymmetric structure, on or off axis.

In the mid-1990s, Yong Ho’s work expanded to two-stream beam instabilities. He rightly foresaw that such instabilities could potentially limit the performance of KEKB and organised and co-organised several international workshops to address this issue early on. Subsequently, he was put in charge of the development and modelling of the X-band klystron for the JLC. He also greatly contributed to the development of the multi-beam klystron now in use for large superconducting linacs, and to the optimisation of the J-PARC accelerators.

Yong Ho returned to the field of collective effects more than 10 years ago and he remained extremely active there. Over the past few years, together with two other renowned accelerator physicists, Alexander W Chao and Michael Blaskiewicz, he developed a two-particle model to study the effects of space–charge force on transverse coherent beam instabilities. The purpose of this model was to obtain a simple picture of some of the essence of the physics of this intricate subject and at the same time provide a good starting point for newcomers joining the effort to solve this long-lasting issue.

As illustrated by his role as chair of an ICFA panel, and by his co-organisation of a large number of international workshops and conferences (including PAC and LINAC), Yong Ho was devoted to serving the international physics community. He was a productive author, diligent referee and esteemed editor for several journals. In 2015 he was recognised with an Outstanding Referee Award by the American Physical Society, and just a few months ago, in the summer of 2018, Yong Ho was appointed associate editor of Physical Review Accelerators and Beams.

Yong Ho was a very good lecturer, teaching at different accelerator schools, including the CERN Accelerator School. He was also in charge of a collaboration programme in which young accelerator scientists were invited to spend a few weeks at KEK.

Yong Ho was a wonderful person and an outstanding scientist. We are very proud to have had the chance to work and collaborate with him. His passing away is a great loss to the community and he will be sorely missed.

His friends and colleagues at CERN.

Albert Hofmann 1933–2018

An expert in all things colliders

Albert Hofmann

Albert Hofmann, a brilliant accelerator physicist with a worldwide reputation and a distinguished career in the US and Europe, passed away on 28 December 2018.

Hofmann finished his studies at ETH Zurich in the mid-1960s and went on to work at the Cambridge Electron Accelerator (CEA) at Harvard University. The team at CEA was a highly reputed one, making seminal contributions including the invention of the low-beta scheme, which converted the CEA 6 GeV electron synchrotron into an electron–positron collider where the first indications of the charm quark were revealed. This scheme, used in the accelerator’s by-pass, became a basic ingredient of modern colliders.

A major element of this conversion was a Robinson damping wiggler – a series of magnets that supresses a beam instability brought about by synchrotron radiation. Hofmann led the design, installation and commissioning of this complex device. This was the first multipole wiggler to be used in an electron synchrotron ring, and led to Hofmann’s subsequent lifelong interest in the new discipline of synchrotron radiation and his monumental book The Physics of Synchrotron Radiation.

When the CEA closed Hofmann moved to CERN in 1973, where he made significant contributions to the performance of the Intersecting Storage Rings (ISR) collider, including proposing the use of a higher harmonic cavity to control beam stability as had been done at CEA.

When the ISR was closed a decade later, Hofmann returned to the US, accepting a professorship at Stanford University. He worked on the damping rings for the SLC electron–positron linear collider and on synchrotron-radiation devices such as the wiggler and undulator magnets to be inserted into the PEP and SPEAR electron–positron circular colliders.

Hofmann was then invited to return to CERN to take joint responsibility for the commissioning of the large electron–positron collider (LEP), and made remarkable contributions to its performance throughout the collider’s 11 years of operations. As at the ISR, he was especially fond of subtle effects such as those of tidal forces on the collider’s beam energy, which was crucial for the precision of the experimental programme.

He subsequently returned to California to work on a compact light source based on inverse Compton scattering that was under development by Lyncean Technologies Inc in Palo Alto. Here, he brought his deep knowledge of accelerator physics to bear on the unusual situation of a very-low-energy electron storage ring. This knowledge was key to the success of this light source.

Hofmann gave many inspiring lectures at the CERN Accelerator School, simplifying, as only he could, some of the most difficult concepts in accelerator physics. He also served as advisor for a number of synchrotron-radiation facilities, spanning from the European Synchrotron Radiation Facility (ESRF) in Grenoble to the Synchrotron Radiation Research Centre (SRRC) in Taiwan. In 1996 he was awarded the prestigious Robert R. Wilson Prize of the American Physical Society for his achievements in accelerator physics and teaching.

Albert Hofmann was always over-generous in giving scientific credit to colleagues who had in some cases only made a minor contribution. He also had an impish, tongue-in-cheek sense of humour and told fascinating stories about the early days of colliders. We say goodbye to this generous, modest, inspiring and unpretentious role model.

His friends and colleagues at CERN and SLAC.

 

Vladimir Rittenberg 1934–2018

Striving for essentials

Vladimir Rittenberg

Vladimir Rittenberg, a distinguished theoretical physicist, passed away on 15 April 2018. Vladimir was born in 1934 in Bucharest, Romania, to a mother from Galati, eastern Romania, and a father, an engineer, from Bessarabia, now Moldavia. He attended the French School in Bucharest, after which he earned a diploma in technology from the Bucharest Electrotechnical School. Starting in 1952, Vladimir studied theoretical physics at the University of Bucharest, passing the MSc exam in 1957. Due to political upheaval, Vladimir was forced to leave the university in 1958 and accept a job in a laboratory for crystal growth. It was only in 1963 that he was able to return to theoretical physics, joining the high-energy physics group of the Romanian Academy. In 1966 he received a PhD and became the leader of the group.

In 1969 Vladimir finally left Romania. This was facilitated through an invitation to Oxford University arranged by Bruno Renner. In the same year he immigrated to Israel, where he was a visiting scientist at the Weizmann Institute until 1972. Thereafter, for three years, he worked at the Rockefeller University in New York. In 1975 Vladimir was appointed professor at the University of Bonn in Germany. He kept this position for more than 40 years, but also followed many invitations to spend time abroad: for example, once more at Rockefeller University, several times at the International School for Advanced Studies (SISSA) in Trieste, at the University of Melbourne, the Dubna Laboratories and various places in France. In his later years he also visited the Federal University of São Carlos in Brazil many times.

Vladimir’s early papers – 19 in total between 1966 and 1969, mostly with Ladislaus Banyai as co-author – were devoted to particle theory and the related group theory. In the following five years Vladimir collaborated with various colleagues from the Weizmann Institute and Rockefeller University, producing 25 papers on phenomenological high-energy physics. On his arrival in Bonn, his main interest turned to the mathematics of representations of super­algebras related to supersymmetrical quantum field theories. With Werner Nahm and Manfred Scheunert, and later with Daniel Wyler, he published several papers that were seminal to the subject and relevant for string theory.

At the beginning of the 1980s Vladimir successfully conquered the new domain of spin field models, in particular those related to the then newly revived two-dimensional conformal field theories. In this area of mathematical physics he produced more than 50 articles, partially in collaboration with his students or colleagues in Bonn, or visitors to the Bonn physics department. He obtained several first results about the level structure of quantum spin chains using conformal invariance, which were useful in the early stages of string theory.

From 1993 Vladimir turned his attention to non-equilibrium statistical processes such as reaction–diffusion phenomena. He showed how in one dimension, similar to equilibrium processes, some of these non-equilibrium processes can be described through quantum spin chain models too, partly exploiting quadratic algebras. This resulted in 25 articles written with various collaborators, in particular Francisco Alcaraz. With Francisco he constructed the first stochastic model that is integrable and conformally invariant. Vladimir was also the founding editor of the Journal of Statistical Mechanics, which launched in 2004.

Vladimir was very passionate in scientific discussions, always striving to get a better understanding of the underlying physics. He had an extraordinary gift of connecting with people, which was clearly visible through the huge number of researchers who were his co-authors. He also inspired young people to enthusiastically follow his guide into the adventure of scientific research.

Vladimir is survived by his daughter Vivian and three grandchildren.

Rainald Flume and Günter v Gehlen the University of Bonn.

 

Pio Picchi 1942–2019

A leader in detector development

Pio Picchi

Pio Picchi, a prominent Italian particle physicist, suddenly passed away on 23 January. It was a shock for everyone who knew him as a mentor and as a splendid friend.

We had the great honour and pleasure of collaborating with Pio over the past few decades. He had an honest and unbiased scientific approach to experimental particle physics, often along the lines of his exceptional intuition, and had many insightful ideas at the frontiers of detector technologies.

Pio spent most of his life as a physicist, first at the INFN Frascati National Laboratories in Italy, and then at the University of Turin, where he was appointed full professor at the age of 34. In his research, mostly conducted at CERN, he gave visible contributions to the design and construction of several experiments such as FRAMM and ALEPH at CERN, NUSEX in the Mont Blanc underground laboratory, and LVD and ICARUS at the INFN Gran Sasso National Laboratory.

To mention a few of his achievements, it was under Pio’s leadership that the first tonne-scale liquid–argon time-projection chamber detector was successfully operated at CERN within the ICARUS R&D programme; he pioneered, also at CERN, the double-phase operation mode of xenon and argon time-projection chambers, which nowadays is widely used in dark-matter experiments; and he actively participated in R&D on new micropattern detectors.

Since a relatively young age, Pio was affected by Parkinson’s disease. Thanks to his courage and tenacity against his evolving illness, he continued to work at his best. CERN was a place of joy for him. On days with physicians’ visits, he would be upset because that prevented him from going to work. For us, his presence provided an anchor to hear the latest news and to discuss not only physics but also life. Even on his very last day at CERN, Pio was discussing with students new ideas on single-photon detection in liquid argon and the way to test them. He had the gift of always recognising and valuing the best skills of every person around him: students, technical personnel, colleagues and friends. And he always did so without asking for anything in return.

We will remember Pio as a generous man with a strong sense of friendship. Those who needed help found a friend that was always available and discreet: if he could help, he would do it with modesty and confidentiality.

His friends and colleagues at CERN and beyond.