Development of a test stand for semiconductor photocathodes with beamline for 60 keV spin-polarized electrons

A test facility for Photo-Cathode Activation, Test and Cleaning using atomic-Hydrogen (Photo- CATCH) is being constructed at the Institute for Nuclear Physics (IKP) which houses the Superconducting Darmstadt Linear Accelerator (S-DALINAC). In addition to the conventional thermionic source, a Spin-Polarized electron Injector (SPIn), based on photoemission from a semiconductor photocathode has been installed for future experiments with polarized beams. Varying degrees of polarization is achieved depending on the crystal structure and preparation of the cathodes. In order to improve the performance of the photoelectron source, systematic studies in terms of quantum efficiency (QE), cathode rejuvenation, vacuum lifetime, charge lifetime and polarization have to be conducted on different photocathode types. These factors strongly depend on handling of the cathode, the vacuum condition in the chambers, cathode surface cleaning as well as preservation of stoichiometry, negative electron affinity (NEA) activation of the cathode and the type and structure of the semiconductor material. With Photo-CATCH, experiments such as atomic-hydrogen cleaning of the sample, multi-alkali and oxidant NEA activation of the cathode and tests of QE, P and lifetimes can be performed in an improved vacuum. Additionally, experiments with polarized-electron beam of up to 60 keV are foreseen. (author)