ERL09 WG1 summary; DC gun technological challenges

Nishimori, Nobuyuki; Bazarov, I.*; Dunham, B.*; Grames, J.*; Hernandez-Garcia, C.*; Jones, L.*; Militsyn, B.*; Poelker, M.*; Surles-Law, K.*; Yamamoto, Masahiro*

This paper summarizes technological challenges of photoemission DC guns being developed for the future energy recovery linac (ERL) light sources (LS). Anticipated new applications of ERL-LS demand an electron gun capable of producing an extremely low emittance beam at very high average current. The low emittance requires unprecedentedly high voltage equal to or greater than 500 kV between cathode/anode electrodes together with high accelerating gradient on the photocathode. The technological challenge is to develop a high voltage insulator system, which can withstand field emission from the electrodes. The high average current requires prolonged cathode life time, which is governed by ion back-bombardment. Challenges to mitigate the cathode damage caused by ion back-bompardment are surveyed. A gun geometry satisfying both high gun voltage and high accelerating gradient is also proposed.