Multiple charge transfer between HCI and neutral atoms

Interactions between highly charged ions and neutral atoms are of interest for the fundamental understanding of plasmas and star formation. Moreover, it is an interesting system in itself, since it allows to study the dynamics in quantum mechanical many-body systems. Depending on the interaction energy of the ion-atom system, three different processes may occur: For projectile velocities higher than the active electron's orbital velocity, impact ionization is dominant; for comparable velocities, excitation or resonance phenomena can occur; whereas for lower velocities, impact ionization can be neglected and electron transfer is dominant. We have performed experiments at the KVI Groningen to investigate double charge transfer in the low energy regime for the O(6+)+Na(3s) system. For the first time, the energy dependence of double electron transfer in alkali-ion collisions was measured and a strong dependence of the relative cross sections on the collision energy was found. Furthermore, we present a new setup that will be installed at the HITRAP beamline for further experiments on multiple charge transfer. It consists of a dense cold atom sample trapped at the center of a high resolution recoil ion momentum spectrometer. Atoms are pre-cooled in a two-dimensional magnetooptical trap (2D MOT), which delivers a cold atom beam with a longitudinal velocity spread of 3,5m/s and a low divergence of 23 mrad. This cold atom beam can serve as a target itself or be used as a source for loading a high density target magneto-optical trap, where densities up to 2x1011 atoms/cm³ are reached.