ELECTRON COOLING FORCES FOR HIGHLY-CHARGED IONS IN THE ESR

In the ESR storage ring fully stripped ions up to uranium have been st ored and cooled at beam energies between 50 and 370 MeV/u. Longitudina l cooling forces for heavy ions from C6+ to U92+ at various energies h ave been measured with the ESR electron cooler. Two experimental metho ds have been established which allow the determination of the cooling force for relative ion velocities from zero to 10(7) m/s. At low veloc ities the equilibrium between cooling and longitudinal heating with rf noise is used. For high relative velocities the cooling force is dedu ced from the momentum drift of the ion beam after a rapid change of th e electron energy. Measurements for several ion species are presented which show a pronounced deviation from the expected q(2) scaling in th e regime of the magnetic cooling force. Further investigations have be en performed to study the influence of magnetic held strength and beam energy on the longitudinal cooling force.