Performance of the thermionic RF gun injector for the linac-based IR free electron laser at the FEL-SUT

Kawasaki Heavy Industries, Ltd. (KHI) has developed a linac-based compact IR free electron laser device and has installed it in the FEL-SUT (IR FEL Research Center of Science University of Tokyo). The FEL device adopts a combination of a multi-cell RF gun with a thermionic cathode and an α-magnet as an injector. The fundamental design of this RF gun is the π/2 mode standing wave structure. It has two accelerating cells and a coupling cell located on the beam axis, a so-called “on axis coupled structure” (OCS). Characteristics of momentum distribution and micropulse bunch length of the electron beam are compared with beam dynamics simulation results in this paper. We succeeded in obtaining sufficient peak current for FEL lasing with this injector, and the first lasing was achieved on 6 July 2000.