Photocathodes for SRF Gun
Photocathodes play a key role in all photo-injector systems. With the strong connection to the laser system, the choice of the optimum cathode type and its further improvement is a main issue for the progress in photoinjectors. Cs2Te photocathodes are developed to be the standard photocathodes in our SRF gun. Meanwhile, GaAs (Cs, O), Cs3Sb and GaN (Cs) photocathodes are also exploited to search new materials with high quantum efficiency (Q.E.) for high current electron sources.
The SRF gun has rigorous requirements for the cathodes, including Q.E.>1% in a lifetime over 100 hours, the least contamination and heat load to superconducting Nb cavity, being robust against high laser intensity and low reflective, no C or H element on the surface of the plug, and also low dark current. To fulfill these requirements, the SRF gun works always in ultra-high vacuum, and the development of preparation chamber, transport system, cathode tuning and cooling system is important.