New light on electron—ion collisions from heavy–ion storage ring experiments

Abstract

Experiments with merged beams of electrons and ions stored in accelerator rings have provided a wealth of new data on electronion collision processes. The development towards lower and lower temperatures of electron beams and the availability of brillant beams of ions up to the highest charge states has opened up a precision atomic spectroscopy through the observation of resonances. The available technology also provides unique new access to very low electronion collision energies. There, typically below a few millielectronvolts, an unexpected enhancement is observed in the recombination of atomic ions with electrons. For U28 ions, where such enhancement was seen for the first time, the measured rate coefficient is roughly a factor of 200 higher than expectation for radiative recombination. The experimental spectrum can be simulated by assuming dielectronic recombination (DR) resonances at very low energies. However, recombination enhancements are also observed with completely stripped ions where no DR re...