Varian is carrying out the development of a high-power, CW gyrotron at a frequency of 110 GHz. The design of a tube capable of generating an output power of 1MW CW has recently been completed. The tube will employ a TE22,2,1-mode cavity and utilize an output coupling concept where the collection of the spent electron beam is separated from the outgoing microwave power.
"Design of a 1 mw gyrotron with beam/RF separation", Proc. SPIE 1576, 16th International Conference on Infrared and Millimeter Waves, 15761P (1 October 1991); doi: 10.1117/12.2297774; https://doi.org/10.1117/12.2297774