Stability limits of cooled beams Parkhomchuk V.V. BINP, Novosibirsk-90, Russia Workshop on “Beam Cooling and Related Topics” 255,WE-Heraeus-Seminar 14-18 May 2001 Abstract The cooling itself used for damping single particle oscillations and coherent oscillations of ion beams. But extremely high phase space density of the ion beam after cooling can be a source of stability problems. These problems were a subject of discussions on many conferences, workshops and accelerator schools. Let in this report concentrates on a specific instability that is manifested itself by beam emittance blow-up and the ion beam losses at the storage ring with the electron cooling - the so called “electron heating”. For storage rings CELSIUS, COSY, Indiana Cooler this is a serious problem that limits the use of the electron cooling in physical experiments. 1. Introduction The problems of stability in existing cooling rings were a subject of many discussions and reports. The most resent report was presented at proceedings of ECOOL99 . These problems were found to exist at many storage rings. Usually, these problems only briefly mentioned at the status cooler ring reports and private communications. For introduction of the problems let’s demonstrate the phenomenon based on the same specific (may be particular) results more or less known to the author. In SIS cooler  was observed development of oscillations in the ion beam at the time of accumulation high ion current (as role lighter ions when the injection current higher). Figure 1 presents an example of accumulation Kr 34+ beam at an energy of 11 MeV/u, and the electron beam cooling current 0.5 A. ion beam current (mA) 6 4 2 0 Kr 34+ current signal pickup electrodes 10 20 30 40 time (s) Figure 1. Accumulation of Kr beam at SIS, the upper line is the ion current, down points is a signal of pickup electrodes sensitive to the space charge fluctuation in the ion beam.