State-of-the-art electron guns and injector designs for energy recovery linacs (ERL)

A key technology issue of energy recovery linac (ERL) high-power free-electron laser (FEL) and fourth generation light sources is the demonstration of reliable, high-brightness, high-power injector operation. Ongoing programs that target up to 0.5 A injector performance at emittance values consistent with the requirements of these applications, are described. There are three approaches that could deliver the specified performance. These are DC photocathode guns with superconducting RF (SRF) booster cryomodules, high-current normal-conducting RF (NCRF) photoinjectors that may also use SRF boosters, and SRF photocathode guns and boosters. The achieved performance at existing ERL facilities, the status of ongoing source development programs, and the proposed parameters of the injectors for planned ERL facilities are described and compared. As examples, we concentrate on three high-current injectors being developed by Advanced Energy Systems (AES) with collaborators at the Thomas Jefferson National Accelerator Facility (JLAB), Los Alamos (LANL) and Brookhaven (BNL) National Laboratories.