Photocathodes as electron sources for high resolution merged beam experiments

Abstract

An ultra cold electron source was developed for the storage ring TSR in Heidelberg to study electron-ion interactions with high energy resolution. The heart of the source is a GaAs photocathode which emits electrons with energy spreads below 10 meV. Photoemitted electrons are extracted in the space charge mode and then undergo adiabatic magnetic expansion and adiabatic acceleration to obtain an ultra cold electron beam which is overlapped with the stored ion beam in a straight section of the ring. In the first recombination measurements on HD+ unprecedented energy resolution for low-energy resonances was found, demonstrating a transverse and longitudinal temperature of the electron beam of about 0.5 meV and 0.02 meV, respectively.