Investigation of a Multi-Gap, High-Voltage Isolator for a Gyro-TWT With Depressed Collector

The depressed collector is an effective approach to further improve the overall efficiency of high-frequency gyrotron traveling wave tubes (gyro-TWTs). In this article, a multi-gap output isolator is proposed. With similar topologies based on the single-gap output isolator, the multi-gap output isolator offers advantages such as high breakdown voltage, improved microwave transmission, and reduced microwave leakage. The ${Q}$ -band TE01 mode single gap (gap of 2.2 $\times $ 1 mm) and triple gap (gap of 1 $\times $ 3 mm) output isolators are designed and compared in terms of microwave performance and breakdown voltage. Then microwave amplification and beam energy recovery are discussed based on a ${Q}$ -band gyro-TWT with a triple-gap output isolator. Simulation results demonstrate that when driven by a 60-kV to 9.65-A electron beam, the device can stably produce a maximum output power of 205 and 193 kW of recycled power at 47 GHz with a 20-kV depressed collector. The overall efficiency is effectively increased from 35.4% to 53.1%. The mode converter and triple-gap output isolator are fabricated and experimented. Cold test results show that ${S}_{{11}}$ is lower than −13 dB, ${S}_{{21}}$ is greater than −1.3 dB, and are in good agreement with the simulation results. Furthermore, a maximum breakdown voltage of 70.7 kV is measured in the experiment. These investigations provide ideas for achieving efficient operation of high-frequency gyro-TWTs.