The paper presents the results of research is carried out in the Institute of Applied Physics and is aimed at creating a CW submillimeter gyrotrons with an output power of several tens of watts. Results of experiments on the 258 GHz gyrotron at the second harmonic of the gyrofrequency are presented. In the course of experiments maximum output power of 200 W and the relative stability of the output frequency at 5 · 10−6 for the hours-long continuous operation of the gyrotron were achieved.
