Design and numerical simulation of a 94 GHz gyrotron with gradually tapered cavity

Through analysing the coupling coefficient of the generalised telegraphists equations, an optimized 94 GHz gyrotron with gradually tapered cavity is designed. An output power of about 120 kW,corresponding to 41% efficiency, and an oscillation frequency of 94.099 GHz are achieved with a 50 kV, 6 A helical electron beam with a pitch angle of 1.4 at a guiding magnetic field of 3.548 5 T. Compared with the line-joint cavity, the purity of the operating mode is enhanced above 27 dB and the efficiency increases about 7% in the gyrotron with gradually tapered cavity. The efficiency of the beam-wave interaction calculated by the code based on the self-consistent nonlinear theory is in well accord with that simulated by PIC.