Frequency-Tunable Sub-THz Gyrotron with External Reflectors: Design and Simulations

We describe the design of a frequency-tunable gyrotron based on a combination of a low-Q irregular cavity and a frequency-tunable narrow-band external reflector. The frequency tuning in this device is provided by mechanical changing the operating frequency of the reflector placed outside the vacuum zone. The cavity profile is optimized from the point of view of ensuring broadband frequency tuning when the reflection of the output wave signal is provided. At the same time, self-excitation of any wave should be absent in the operating ranges of the magnetic field and the electron current in the case when the reflection is absent. The design is based on detailed simulations predicting possibilities for creation of a gyrotron with high (tens of percent) efficiencies provided in a wide 125–137 GHz) band of the continuous frequency tuning.