Efficient Frequency Step-Tunable Megawatt-Class $D$ -Band Gyrotron

Results of experimental studies on the frequency step-tunable (D-band) megawatt-class gyrotron, which is under development at IHM (KIT), are presented. The goal of the short pulse (0.5 ms) experiments was to study the performance of the gyrotron equipped with a longer cylindrical part of the cavity (higher quality factor) in comparison with the previous results. The new design of the cavity was numerically optimized using the EURIDICE code. The results of numerical studies are presented. It was found that output power and efficiency are increased in this new configuration. The output efficiency of 37% at 1210 kW output power was achieved operating in the TE23,8 mode at 143.4 GHz. With increased beam current, for the same cavity mode, the highest power of 1440 kW was obtained at 35% efficiency. The measurements were repeated for a number of different operating modes. The excited mode with the highest frequency is the TE28,9 mode at an operating frequency of 169.2 GHz.