Kjell Johnsen, one of the accelerator pioneers at CERN and the builder of the ISR, the world's first proton–proton collider, passed away at his home in La Rippe, Switzerland (near Geneva) on 18 July 2007 following a long battle with cancer.
Kjell was born in Norway on June 11, 1921 and studied electrical engineering at the Technical University of Trondheim, where he received the doctorate degree in 1954. He spent 15 months with Dr. Gabor at Imperial College in London. He was selected by Odd Dahl of Bergen, one of the founding fathers of CERN, to take part in the early studies for the accelerators of the future European physics centre, joining the CERN study group in 1952.
Parallel projects for alternating-gradient proton synchrotrons were launched at Brookhaven and CERN in 1952. The two projects cooperated closely in the ensuing years, and Kjell was a frequent visitor at Brookhaven, exchanging ideas with the BNL group; he was a key contributor to the success of both projects. He soon developed into one of the foremost accelerator experts in the world.
Following the completion of the PS at CERN and the AGS at Brookhaven, CERN and the US went on to different next steps. CERN chose the daring project of the Intersecting Storage Rings (ISR), the world's first proton proton collider, and the project proceeded under Kjell's leadership.
Construction began in 1966 with completion in 1971. At the time, the ISR was an incredibly ambitious and controversial project. Many eminent scientists expressed concerns that the beams would not survive long enough to produce physics data. It is now history that the ISR is one of the great accelerator success stories. It opened up a new energy domain for high-energy physics and paved the way for many larger projects, such as converting CERN's SPS into a proton antiproton collider, the Tevatron at Fermilab, RHIC at Brookhaven and, now, the LHC. Under Kjell's leadership, the ISR project was an inspiring example of well-directed teamwork. For all of us who had the privilege to work on this machine under him, we can honestly say that this was a rewarding and uniquely major scientific experience and adventure.
In 1980 Kjell came to Brookhaven as the technical director of the ISABELLE project, a planned proton–proton collider for 400 GeV. But, even though the technical problems of the project were solved, it was abandoned in 1982. Kjell returned to CERN. While at Brookhaven, he was also a visiting professor at MIT.
Kjell was appointed professor at the Technical University of Trondheim in 1957, but returned to CERN 2 years later. Later he was appointed part time professor at the University of Bergen, and for several years he dedicated an important part of his time to teaching at doctoral level and training young people.
In 1990 the American Physical Society honored him with the R. R. Wilson prize for Achievements in the Physics of Particle Accelerators. The citation reads: "For his seminal contribution to the physics, design, construction and performance of the CERN ISR . This highly successful first high energy collider broke the ground for even larger machines of this type, which are now in operation or in the planning stage, opening new frontiers in particle physics".
He was elected an honorary member of the Norwegian Academy of Sciences.
He was also the creator and inaugural director of the CERN Accelerator School, which has become a successful enterprise, attracting many talented and gifted young students from all over the world, and thereby promoting scientific collaboration at a European and worldwide level.
He continued his involvement past retirement. Among other things, he was chairman of the HERA Machine Committee, DESY, and wrote with P. Bryant the book "Principles of Circular Accelerators" (Cambridge University Press).
Kjell's many friends around the world have always valued his kindness, competence, intellectual honesty, seriousness, scientific vision, courage and dedication. It was to him that people always went for clarifications, advice and guidance.
We will miss him dearly. We should, however, be comforted by the thought that he has been a great example and role model to many of us. He has been respected and appreciated, and has most definitely left a permanent mark in his chosen professional field of accelerator research.
