A resonator consisting of three successive cavities with different radii is proposed for a step-tunable gyrotron. Different frequencies of the operating mode can be excited in individual cavities by means of changing the beam radius and the strength of the external magnetic field. A resonator for the frequencies 120 GHz, 140 GHz, and 150 GHz, as desired by the JET, is considered for the operating mode as an example. Mode competition in this resonator is investigated theoretically.
"Frequency Step-Tunable Gyrotron", Proc. SPIE 1039, 13th Intl Conf on Infrared and Millimeter Waves, (18 November 1989); doi: 10.1117/12.978449; https://doi.org/10.1117/12.978449