Development of Gyrotron FU CW GVII: a Second Harmonic, Multifrequency Gyrotron that Radiates Gaussian Beams

A sub-THz, second harmonic, multifrequency gyrotron, Gyrotron FU CW GVII, which radiates Gaussian beams, was developed. This device was designed to change the frequency in a stepwise manner in the range from 270 to 420 GHz. In this paper, we present the first experiments conducted using this gyrotron. Nine modes were selected for this study. The oscillation frequency of the selected modes was measured using a heterodyne system. The profiles of the Gaussian beams converted from the modes were assessed using an infrared camera, and the power of these beams was measured using a power meter. The oscillations of the nine second harmonic modes were successfully measured, and Gaussian beams converted from seven oscillation modes were observed. Four second harmonic modes, TE 8,5, TE 6,5 , TE 5,4 , and TE 2,6 , oscillated in a single mode. The power of the beams ranged from 0.2 to 77 W. Even in the case of spurious oscillation of fundamental modes, the beams converted from the second harmonic modes could be separated from the fundamental mode beams by taking advantage of the different radiation directions emitted through the gyrotron window.