Design of Cavity for Quasi-Optical Gyrotron Step-Tunable Across Multiband

The design of a cavity for quasi-optical gyrotron step-tunable across multiband is presented. In order to achieve step-tuning across several bands, a frequency insensitive quasi-optical mode conversion system including a Vlasov-type launcher and several smooth reflectors is adopted. According to the requirements of the mode conversion system, the working mode group of the cavity is selected. The huge difference in quality factor between the high-frequency modes and the low-frequency modes is mitigated with tapered cavity radius, which results in the homogenization of the starting current. The output power and frequency of the cavity are calculated by the multimode time-domain calculation method. The results show that the cavity can realize step tuning of six frequency points in the range of 33-170 GHz, and the output power is distributed between 66 and 135 kW, which meets the requirements of step tuning across multiband.