Investigation of Harmonic Generation in a High-Current Relativistic Gyrotron

Generation of radiation at high harmonics in a high-current relativistic Ka-band gyrotron in the frequency multiplication mode, when the generation of radiation at a high harmonic occurs simultaneously with generation at the frequency of the main resonance, is studied based on three-dimensional PIC modeling. It is shown that the ratio of the radiation power level at third harmonic to the generation level at the fundamental cyclotron resonance can be about 0.5%, which is several orders of magnitude higher than the values achievable in gyrotrons with weakly relativistic electron beams. Thus, since the output power at the fundamental frequency was 170 MW, the calculated power of radiation at high harmonics reaches the sub-megawatt level. An experimental study of a high-current relativistic Ka-band gyrotron with beam compression in an electron-optical system was performed. A signal at the triple frequency of the main cyclotron resonance was found in the observed spectrum of the output radiation.