A fast frequency step-tunable 236 GHz gyrotron design for DEMO

As part of the EUROfusion WP HCD EC project, the conceptual design of a 1 MW, 236 GHz hollow-cavity gyrotron is ongoing at IHM, KIT for a Demonstration Power Plant (DEMO), along with the 2 MW coaxial-cavity design concept. Fast frequency-tunable gyrotrons (tuning within a few seconds) are recommended for plasma stabilization using a non-movable antenna. In this work, the mode-selection approach for such a frequency-tunable gyrotron is presented and suitable operating modes for fast frequency tunability are suggested. Magnetic field tuning has been confirmed as an effective technique to tune the gyrotron operating frequency. The step-tunability of the 236 GHz gyrotron within the frequency range of ±10 GHz in steps of 2-3 GHz is demonstrated in numerical simulations.