Variable-energy microtron-injector for a compact wide-band FIR free electron laser

A microtron-injector (Proceedings of the 2001 Particle Accelerator Conference, USA, 2001, 2739) for the KAERI compact far infrared free electron laser (FIR FEL) facility has been upgraded to provide tuning of the FEL wavelength from 100 μm to more than 300 μm. The wide-band tunability of the radiation has been achieved by changing the kinetic energy of the accelerated electrons from 6.5 to 4.9 MeV. To do so, the position of an RF cavity inside the microtron is movable within the range of ∼170 mm, and it changes the maximum orbit number of the electrons from 12 to 8. Dependence of the electron beam parameters on the orbit number has been investigated to choose acceptable operating conditions of the microtron for stable operation of the wide-band FIR FEL. Measured parameters of the electron beam and corresponding lasing results of the FIR FEL are presented and discussed.