Photoemission Studies on BNL/AES/JLAB all Niobium, Superconducting RF Injector

Photoelectrons from an all niobium superconducting injector have been generated for the first time. QE of 2×10^-6at 266 nm and 2x10^-5at 248 nm, maximum charge of 10 nC in 10 ns and charge/cycle of 0.8 nC were measured. The lower QE observed after laser cleaning, compared to the room temperature measurements, is attributed to the long distance between the cathode and the closest ion pump and the possibility of the laser ablated material adsorbed back onto the cathode surface at cryogenic temperature. No cavity quenching has been observed even at the maximum laser energy of 3 mJ, maximum repetition rate of 250 Hz and maximum charge of 10 nC from the cathode.