It is with great emotion and deep sadness that we learnt of the loss of our colleague and friend Dieter Möhl on 24 May. An accelerator physicist of world reputation, he made essential contributions to many projects at CERN and around the world. Here at CERN his name will remain forever linked with the success of the antiproton programme from its very beginning, but he also made substantial contributions to the FAIR project in Germany and to many other storage rings where beam cooling was an essential ingredient. His theoretical work was unique for the understanding, improvement and extension of beam cooling techniques to many accelerators and storage rings.

He was one of the pioneers who demonstrated by the Initial Cooling Experiment (ICE) that stochastic cooling was a viable proposition. This was essential for the approval of the CERN antiproton programme and its success. He was a leading member of the team which initiated and designed the Low Energy Antiproton Ring (LEAR) where the first ultra-slow beam extraction to experiments - extending over hours - was performed.

After the decision to stop LEAR Dieter actively participated in the study and design of a simplified antiproton source that later became the Antiproton Decelerator ring (AD). This after the SUPERLEAR project - of which he was one of the prominent promoters - was not approved.

He also participated in the study of the Extra-Low Energy Antiproton ring (ELENA) back in 1982 and he was very happy to see that in 2011 this project, which will provide antiprotons with a kinetic energy as low as 100keV, was finally approved in AD. Dieter also made important contributions to electron cooling, a token of this is found in AD and in the modified LEAR machine that became the Low Energy Ion Ring (LEIR). LEIR acts as a buffer and accumulation ring between the fast-cycling ion-Linac 3 and the slow-cycling PS and is an essential element in the LHC ion-injector chain.

Dieter was not only a famous accelerator physicist but also played an important role in human rights issues, in particular in the framework of the Orlov Committee created at CERN. He was one of the founding fathers of this group that aimed to provide efficient help to Soviet dissidents in the 1970s and 80s.

Though he retired in 2001, Dieter continued to come to work nearly every day to help us in our projects and to give us advice. Even the day before his untimely death, he was at CERN to discuss the ELENA project with us. He was one of the kindest, gentlest people we have ever known, with infinite patience and proverbial generosity. We gratefully remember Dieter’s human quality and we miss his wise counsel.

His friends and colleagues