Wolfgang Schnell (1929 - 2006)

Wolfgang Schnell in 2004, displaying a piece of equipment for the CLIC test facility.

Wolfgang Schnell passed away on 2nd October after an illness which he endured with great courage and lucidity. Wolfgang was one of CERN's pioneers and made numerous significant contributions to the field of accelerator physics and technology throughout his career. After obtaining a degree in physics from the University of Heidelberg, he worked at the Max-Planck Institute, before joining the PS construction team in 1954.

When working in the group led by Chris Schmelzer in 1959, he achieved a breakthrough during the running-in of the PS, which suffered from substantial beam loss during acceleration. With the phase-lock feed-back system built by Wolfgang, the beam went immediately to 24 GeV with hardly any losses. He was proud to show later that the electronics of his system had been built inside a coffee tin.

Wolfgang Schnell with John Adams, leader of the PS project, in the famous picture which marked the start-up of the PS accelerator in 1959. From left to right: John Adams, Hans Geibel, Hildred Blewett, Chris Schmelzer, Llyod Smith, Wolfgang Schnell and Pierre Germain (with his back to the camera).

Wolfgang then became a member of the design team that studied the next generation of CERN accelerators after the PS - the Super Proton Synchrotron (SPS) and the Intersecting Storage Rings (ISR) - and made significant contributions to both.

He proposed a travelling-wave structure for the 300 GeV synchrotron for the acceleration of the particles, which are nearly relativistic at injection energy. Such a structure is still in use in the SPS, faithfully accelerating protons and ions since 1976.

The ISR was the first ever proton-proton collider, and operated from 1973 to 1983. Wolfgang led the design and construction of the radio frequency (RF) system and implemented many improvements during the lifetime of the ISR. He was responsible for the running-in and the performance improvements of this tricky accelerator (its final luminosity was 35 times the design value). During this period, he discovered the transverse Schottky signal, a type of noise generated by the random transverse motion of the particles. It was immediately put to good use to investigate the betatron frequencies of the dc beam, which previously could not be measured. The discovery of this signal led to another of Wolfgang's unique accomplishment: the resurrection and the first experimental proof of stochastic cooling of beams, based on the concept invented by Simon van der Meer in 1968, which was considered to be without any practical application at the time. It opened the door to antiproton cooling and, consequently, to proton-antiproton collisions, a technique which was highly successful in the SPS, and still is in the Tevatron.

In 1983 the ISR was closed in favour of LEP, and Wolfgang was one of the leaders of the initial study group. He went on to be the driving force of the LEP RF group, which constructed the largest and most complex RF system in the world based on copper cavities. In the same year, he was the first (with S. Myers) to present a paper on the parameters of a future proton-proton collider in the LEP tunnel (the present LHC) and participated actively in the brainstorming on CERN's future in 1985. In this framework he proposed a more practical variant of a two-beam scheme for a linear e+e- collider. This has the potential to reach the highest energies and is still being studied at CERN as the Compact Linear Collider (CLIC). Wolfgang led this study with great enthusiasm for almost 10 years and contributed to various novel ideas even after his retirement.

His accomplishments were internationally recognised by his membership in international high-level committees, the Prize for Achievements in Accelerator Physics and Technology in the US, and the award of Doctor h. c. by the University of Heidelberg. He played a leading role in the management of CERN as Department Leader, Division Leader and prominent member of committees and project teams. He was renowned for his lean management whilst keeping a keen eye on the essentials.

Wolfgang will be remembered as a friend and a colleague with an amazing ability to create a team spirit - a natural leader with contagious enthusiasm. He was always approachable, with no barriers for young people to whom he was a patient tutor and mentor. He kept close contacts with technicians and workshop staff to follow the latest developments and to keep his feet on the ground.

Many will be forever proud to have been in one of his teams and to have had the honour to work with him. He will be sorely missed. We would like to extend our heartfelt sympathy and condolences to his wife.

His colleagues and friends