A high performance, 33.2 GHz three-cavity gyroklystron has been designed using a self-consistent simulation code, which for an axial velocity spread of 7% and a=1.5 predicts an output power of 250 kW and an efficiency of 39%. The design modifies Varian's pioneering 28 GHz gyroklystron with a slight increase in frequency, a lower beam a, and an additional buncher cavity in order to yield higher gain and efficiency.
J. D. McNally,
"33.2 GHz, 3-cavity gyroklystron", Proc. SPIE 1929, 17th International Conference on Infrared and Millimeter Waves, 19293K (14 December 1992); doi: 10.1117/12.2298245; https://doi.org/10.1117/12.2298245