A high density target of ultracold atoms and momentum resolved measurements of ion-atom collisions

Abstract

In this thesis an ultracold high density target with high loading flux in combination with a recoil ion momentum spectrometer (RIMS) is presented. Trapped rubidium atoms serve as a high density target (up to 10¹¹ atoms/cm³) at a temperature of only 200 µK. The target is loaded from a two-dimensional magneto-optical trap (2D MOT), which delivers an atom beam with a brilliance of 8 x 10¹² atoms/(s*rad) and a longitudinal momentum spread of 0.25 a.u.. The great advantage of this source is that the cold atom beam can be used as a target itself. The experimental setup, including the RIMS and the targets, are characterized using one-color two-photon ionization experiments. After the successful commissioning presented in this thesis the experiment is ready to be connected to the HITRAP beamline at the GSI Helmholtzzentrum fur Schwerionenforschung, where multiple charge transfer between ultracold atoms and highly charged ions up to bare uranium can be investigated. In a different experimental setup, in collaboration with the KVI in Groningen, the Netherlands, first experiments on the energy dependence of double charge transfer in alkali-ion collisions are preformed. Using RIMS, two distinct double capture mechanisms, sequential transfer and correlated transfer, are identified and the respective differential cross sections are determined. The effective interaction time of the collision is varied by changing the projectile's velocity. At short interaction times the sequential transfer is dominant, while at longer interaction times the correlated transfer becomes more important.