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.

Development of a high average current rf linac thermionic injector

“…Electron injectors can use several different types of cathodes to generate the electrons that are accelerated in the first rf cavity [3,4]. One approach is to use a thermionic cathode located on the axis of the upstream wall of the first accelerating cell.…”

“…Photocathodes can operate at high instantaneous currents and provide electron bunches that have both high quality and high charge per microbunch. For these reasons, they are generally the preferred approach for high-brightness applications [3,4,[12][13][14][15][16]. However, the use of laser photocathodes is a complicated and expensive approach that does not easily scale to robust systems to produce high average beam currents, since there are limitations of the drive lasers as well as limitations due to the thermal loading and lifetime of the photocathodes.…”

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.…”

Design, construction and performance of all niobium superconducting radio frequency electron gun

“…Different technologies such as DC, Normal conducting RF (NCRF) and Superconducting RF (SRF) injectors [3] are being considered for meeting these needs. The key requirements in all these devices are: choice of an efficient, long lived photocathode, efficient coupling of RF power to the electron beam and thermal management.…”