Electron cooling for low-energy antiprotons

Divergence and size of stored ion beams can be reduced superimposing on them an intense, monoenergetic electron beam with little transverse motion ('electron cooling'). The present work first considers the theoretical foundations of the method and then describes the planning and construction of an electron beam device for cooling antiprotons with MeV energies in the storage ring LEAR and CERN. With respect to the quantitative description of the method, the microscopic processes during the damping of the ion motion, the effect of the damping on an ion in a storage ring, and the properties of the intense, magnetically guided electron beam are discussed. Special attention is paid to the improvement of ion beam cooling due to the magnetic field guiding the electron beam. The electron beam device, operated in ultra-high vacuum, and the experience gained during its construction are described; experiments performed during the test period are presented. The work further develops a numerical simulation of electron cooling on the basis of the theory discussed. Given realistic external parameters, the simulation yields cooling times and equilibrium states of the ion beam during electron cooling in a storage ring. Finally, non-destructive methods for measuring the velocity distribution in the electron beam are described, which may prove helpful for optimizing the beam cooling. (orig.)