Predicted Performance of a Dc Beam Driven Fem Oscillator Designed for Fusion Applications at 200-250 Ghz

At the FOM Institute (The Netherlands) a free electron laser using a dc beam with depressed collector is being developed for plasma heating, which will be capable of producing 1 MW cw output over an adjustable tuning range of 200-250 GHz. The basic design parameters for the electron beam, undulator and waveguide circuit are determined using a 3D non-wiggle averaged waveguide mode particle interaction code including ac space charge effects. Novel features of the design include using a step-tapered two-section wiggler to achieve both the high gain (10) and the required efficiency ( approximately 5%) as well as a rectangular corrugated HE11 waveguide circuit to handle the high average power requirements. Results are presented on the FEM performance including dependence on beam emittance, percentage feedback, and operating frequency.