Simulation of a waveguide FEL oscillator using an RF linac

A one-dimensional, multi-frequency simulation code has been developed for FELs which use a waveguide to confine the radiation field. Using this simulation code, we analyzed the spontaneous emission from electron micropulses produced by an RF linac. It is found that for some parameters both high and low frequency waveguide modes are growing simultaneously and the resulting spectrum thus contains two peaks. Finally, the experimentally obtained dependence of the radiation power on cavity length detuning is analyzed.