220GHz confocal waveguide Gyro-TWT with double lossy severs

A 220GHz Confocal Waveguide Gyro-TWT with double lossy working on HE06 mode is designed. With related basic theories, the parameters of confocal waveguide is studied. Based on these parameters, the dispersion curve are calculated. Then, lossy sever confocal is adopted to suppress backward oscillation. Two schemes are explored: single lossy sever, and double sever severs. Both experiments and PIC simulations show that single lossy sever is not enough to suppress backward oscillation for this gyrotron, while Gyro-TWT works well by enough self-oscillation suppression of double lossy severs. For this 220GHz double lossy severs gyro-TWT, PIC simulations show that the peak output power is 10.7kW, the peak efficiency is 11.65%, peak gain is 25.5dB and the 1dB bandwidth is 2.3GHz. Keywords: confocal waveguide, gyro-TWT, particle-in-cell, double lossy severs.