Preliminary Design of a 105-140 GHz Step-Tunable 1 MW Gyrotron

The preliminary design of a 1 MW gyrotron oscillator capable of operation at a range of frequencies between 105 GHz and 140 GHz is presented. Oscillation modes are chosen to yield high efficiency at 105, 118, 127, and 140 GHz, using a single-anode magnetron injection gun. Modes with caustic angles near 60 degrees are employed to ensure efficient conversion to a Gaussian output beam using a numerically optimized dimpled Vlasov launcher and a set of steering and phase-correcting mirrors. A single-stage depressed collector is employed to yield net electrical efficiencies exceeding 50%. Operation at 105 GHz and 140 GHz is feasible with a single-disc CVD diamond output window. For operation at all four design frequencies, a tunable double-disc window is required.