Our dear colleague and friend Karel Cornelis passed away unexpectedly on 20 December 2022.

After finishing his studies in physics at the University of Leuven (Belgium), Karel joined CERN in 1983 as Engineer in Charge of the SPS at the time when the machine was being operated as a proton–antiproton collider. During his career, Karel contributed greatly to the commissioning, performance development and follow-up of the SPS during its various phases as a proton–antiproton collider, a LEP injector, a high-intensity fixed-target machine and an LHC injector of proton and ion beams. Karel had a profound and extensive knowledge of the machine, from complex beam-dynamics aspects to the engineering details of its various systems, and was the reference whenever new beam requirements or modes of operation were discussed.

Karel was an extremely competent and rigorous physicist, but also a generous and dedicated mentor who trained generations of control room technicians, shift leaders and machine physicists and engineers, helping them to grow and take on responsibilities and always remaining available to lend a hand when needed. His positive attitude and humour have left a lasting imprint: “think like a proton: always positive!” has become the motto of the SPS operation team and is now displayed in the SPS island in the CERN Control Centre.

Karel had the rare gift of being able to explain complex phenomena with simple, but accurate models and clear examples, whether in the realm of accelerator physics and technology or of physics and engineering more generally. As an example, Karel gave a fascinating series of machine shutdown lectures covering the history of the SPS, synchrotron radiation and one of his passions, aviation, including a talk on “Air and the Airplanes that Fly in It”.

He was a larger-than-life tutor, friend, reference point, expert and father figure to generations of us and has been much missed in the SPS island and beyond since his retirement in September 2019. He will be even more so now. 

It’s a measure of his generosity of spirit, kindness, enthusiasm and humour that we still look back on the part he played in our lives with much affection. Memories of him grabbing a pen and a piece of paper and explaining anything from beam–beam to where the latest aperture restriction was…

His former colleagues and friends