ELECTRON COOLING WITH AN ULTRACOLD ELECTRON-BEAM

The efficiency of electron cooling can be improved by adiabatically ex panding the electron beam in a decreasing magnetic field, thereby lowe ring the transverse electron temperature. An electron beam expanded by a factor of 10 has been implemented at the CRYRING electron cooler, d ecreasing the transverse electron temperature from 100 to 10 meV. This has resulted in an increased drag force between ions and electrons an d in large reductions of cooling times. Also, the energy resolution in electron-ion recombination experiments at low relative energy has inc reased by a factor of 10.