State-of-the-Art Electron Guns and Injector Designs for Energy Recovery Linacs (ERL)

Abstract

A key technology issue of energy recovery linac (ERL) devices for high-power free-electron laser (FEL) and fourth generation light sources is the demonstration of reliable, high-brightness, high-power injector operation. Three ongoing programs that target up to 0.5 Ampere photocathode injector performance with required EFU brightness, are described. The first is a DC gun and superconducting RF (SRF) booster cryomodule. Such a 748.5 MHz device is being assembled and will be tested up to 100 mA at the Thomas Jefferson National Accelerator Facility (JLAB) beginning in 2006. The second approach is a high-current normal-conducting RF (NCRF) injector. A 700 MHz gun will undergo thermal test in late 2005 at the Los Alamos National Laboratory (LANL), which when equipped with a suitable cathode, would be capable of exceeding 0.5 Ampere operation. Finally, a half-cell 703.75 MHz SRF gun with a diamond amplifier and other cathodes, will be tested to 0.5 Ampere at the Brookhaven National Laboratory (BNL) in 2007. The status and projected performance for each of these injector projects is presented.

R&D ERL: Beam dynamics, parameters, and physics to be learned

“…To provide effective damping of high order mode (HOM) this gun has rather large iris radius of 5 cm. More details on the SRF gun and its photocathode system can be found elsewhere [7]. To keep the beam from the growing in size shortly after being emitted from the cathode, a focusing element in close proximity to the cathode is very desirable.…”

“…Transverse multi-pass BBU can present an insurmountable problem for operations of an ERL. The design of the 5-cell SC BNL cavity [7] was optimized to reduce the quality factor of HOMs and push BBU threshold beyond the ampere level.…”

A CW normal-conductive RF gun for free electron laser and energy recovery linac applications

“…A number of proposed projects in energy recovery linacs (ERL) and linac-based soft-xray-VUV free electron lasers (FEL) requires injection of 100 pC -1 nC electron bunches at repetition rates from kHz to hundreds of MHz [1,2,3,4,5,6,7]. For both ERL and FEL applications, production of high-brightness electron beams is critical in achieving the desired x-ray performance and normalized beam emittances lower than 1 mm mrad are required.…”