Computation of Start Oscillation Current in a gyrotron

Gyrotron is a high power microwave device intensively developed for heating of plasma in thermonuclear fusion research. The relativistic gyrating electron beam interacts with transverse electric (TE) wave near cutoff in a uniform section of tapered cavity resonator at a DC magnetic field helps to excite several modes simultaneously. The efficient operation of the gyrotron requires excitation of desired mode while suppressing competitive modes. Thus, to design gyrotron, analysis of Start Oscillation Current (SOC) is extremely important. SOC plays a critical role in selection of dominating modes and operation of the device at the dominant mode. This paper discusses estimation of start oscillation current (SOC) for 42 GHz, 200 kW gyrotron operating at TE₀₃. A numerical code GCAVSOC to compute the SOC has been developed using MATLAB. Further, the results of SOC also validated with IT-BHU, which shows good agreement.