A comparative study of coaxial and hollow cavities for a 1MW, 280 GHz gyrotron as regards mode excitation is presented. The study indicates that coaxial cavities are less susceptible to parasitic oscillations than hollow cavities. Results obtained here are used to estimate the conditions for stable, single mode operation in the high - efficiency regime.
R. A. Correa,
"Starting current in coaxial gyrotrons", Proc. SPIE 1929, 17th International Conference on Infrared and Millimeter Waves, 192972 (7 December 2017); doi: 10.1117/12.2298371; https://doi.org/10.1117/12.2298371