HIGH-POWER OPERATION OF A WIGGLER-FOCUSED SHEET BEAM FREE-ELECTRON LASER-AMPLIFIER

The proof-of-principle millimeter-wave free electron laser amplifier at the University of Maryland has been operated at an input power level of similar to 1 kW at a frequency of 86 GHz, following successful operation at smaller input power levels at 94 GHz. Significant gain has been achieved at high rf power level with 56 period uniform wiggler in these preliminary studies. The experiments have been performed at 530-570 kV voltages, 5-19 A beam currents, and 2.1-3.65 kG wiggler magnetic fields. Experimental results are in good agreement with theoretical calculations from a one-dimensional simulation code. The discrepancy between the results of 86 GHz and 94 GHz are analysed in terms of electron beam quality, wiggler period error, and waveguide dimension error. The 56 period wiggler has been extended to 74 period with the addition of a 18 period section. Sheet electron beams have propagated through the 74 period wiggler with a newly adjusted wiggler entrance taper. Completion of the proof-of-principle experiments will include saturation studies and the addition of a tapered wiggler section for efficiency enhancement.