Development of Second-Harmonic Terahertz Gyrotrons with Highly Selective Cavities

Mode selection is a key issue for any powerful subterahertz oscillator utilizing oversized cavity. In particular, severe mode competition restrains gyrotron operation at high cyclotron harmonics. To improve the mode selectivity for the open cavities, we use a small resonant groove in the cavity wall in order to scatter all the modes except the chosen one. The proposed method is demonstrated in the experiment with pulsed second-harmonic gyrotron at 1.2 THz, and is used for the design of CW 400 GHz frequency-tunable gyrotron.