Observation of Multi-Peak Frequency Spectrum in A High Power Sub-THz Gyrotron

Equi-distantly distributed multi-peak frequency spectrum was observed in a high power 300 GHz band gyrotron for the case of strong reflection off the vacuum window. An oscillation mode different from the design mode can oscillate by adjusting the magnetic field in the cavity. However, a large fraction of the output wave is reflected by the vacuum window. A theoretical calculation shows that the multi-peak frequency spectrum stems from periodic amplitude oscillation that is caused by mode competition between the oscillating co-rotating mode and the counter-rotating mode originating from the reflected wave.