ELECTRON COOLING OF HOT ION BEAMS

Abstract

Phase space compression of stored ions in storage rings is very important to attain high quality beam. The two most widely used cooling techniques are stochastic cooling and electron cooling. Historically these two methods have been considered complementary in their dependence on the beam and machine parameters. In general, it is accepted that stochastic cooling is well suited for hot ion beams(halo cooling) while electron cooling is more efficient for rather cool ion beams(core cooling). In this work we will present the results of experimental investigations on the possibility of an efficient electron cooling scheme for hot ion beams. Our ultimate goal is to show that conventional electron cooling can be supplemented with adequate relative velocity sweeping techniques in order to achieve efficient cooling even in the case of hot ion beam. The experiments were carried out with the storage ring TSR at MPI fur Kernphysik in Heidelberg. Two different cooling methods have been studied with the purpose of reducing the cooling time of an ion beam with a large momentum spread of ∆P/P=1%. The results of the schemes using an induction accelerator to accelerate the ion beam towards the active region of the cooling force, and the sweeping of the velocity of the electron beam through the velocity range of the ion beam by ramping the cathode voltage are presented. Both methods were tested with a carbon ion beam C of kinetic energy 73.3MeV. Significant reduction of the longitudinal cooling time to 0.65 and 0.35 s is achieved with “induction accelerator sweep” and “electron velocity sweep” methods respectively, compared with 2.9s for conventional cooling. We also show that these two schemes are in fact physically equivalent as shown in figure 1.