The ELSA facility at the University of Bonn uses a storage ring to accelerate polarized electrons up to 3.2 GeV. The photoinjector source is driven by a Ti:Sa laser beam to obtain a high polarization degree (~86%) from a GaAsP strained-layer superlattice crystal photocathode. After a prolonged shutdown of the source we restored its status to fully operational and fine-tuned the laser system, the crystal storage and cleaning apparatus as well as the Linac transfer beamline. The in-house developed diagnostic software FGrabbit has been employed for the analysis of laser and electron beam camera images, providing increased precision and dynamic range in the optimization process. The impact of the crystal cleaning process was studied with spatially resolved quantum efficiency mapping of the photocathode surface.
Switka et al. (Tue,) studied this question.