Possibilities of increase of gyrotron efficiency via frequency locking by external signal

Possibility of efficiency increase of a gyrotron, which frequency is locked by an external monochromatic signal, is studied. Dependencies of orbital efficiency on cyclotron frequency resonance mismatch for different currents of the electron beam are found. It is shown that in multi-mode gyrotron there is a possibility of shifting of frequency-locking zone to the region of parameters corresponding to the optimal efficiency, so efficiency may be significantly increased compared to the free gyrotron.