Coating in Ultra-High Vacuum Cathodic-Arc and Processing of Pb Films on Nb Substrate as Steps in Preparation of Nb-Pb Photocathodes for Radio-frequency, Superconducting e− ^− Guns

A photocathode composed of a Pb layer deposited on Nb substrate is an attractive solution proposed for fully superconducting, radio frequency electron gun to be used in the linear accelerator of the European X-ray free electron laser (Eu-XFEL) operating at Deutsches Elektronen Synchrotron (DESY) and in other, similar devices. Much effort has been put in development of deposition and post-processing of Pb films as superconducting photoemitters. These works led to a satisfactory solution based on lead deposition in a cathodic-arc followed by ex-situ smoothing of the obtained film through its re-melting with a pulsed plasma ion beam. Pb layers obtained by different procedures have been tested for their morphology, microstructure, dark current emission, quantum efficiency and impact on SRF e$^−$ gun performance