Mode analysis of gyrotron oscillation using a k-spectrometer

Experimental analysis of an oscillation mode 500 kW gyrotron at 120 GHz with a TE12,2 whispering gallery mode is reported. Using a k-spectrometer, the oscillation mode was measured. As a result, the oscillation mode was confirmed to be TE12,2 whispering gallery mode, which coincide with the designed value. Also, it is recognized the gyrotron is operated at TE9,3 or TE6,4 mode by adjusting the axial magnetic field. In addition to the major mode, some spurious modes were observed. These modes are considered to be caused by a mode conversion from the main mode in the transmission line between the gyrotron cavity and the k-spectrometer. (author)