Gyrotron frequency stabilization under the influence of external monochromatic signal or wave reflected from the load: Review

We study gyrotron frequency locking by the external monochromatic wave and stabilization of gyrotron frequency by the wave reflected from the non-resonant or resonant load. Although in the last decades influence of the external monochromatic signal and the reflected wave at the gyrotron operation was studied in a number of publications, concrete schemes of gyrotron frequency stabilization weren’t discussed. The study of frequency stabilization by the wave coming into the cavity from the external electrodynamic tract, has become particularly actual after the development in Institute of Applied Physics RAS (IAP RAS) the quasi-optical converter, which allows to transform a large part of wave coming from the output tract into the gyrotron operating mode. We use the fixed field longitudinal structure approximation, which is correct at a sufficiently high Q-factor of gyrotron cavity. This approximation permits us to get analytically some results of influence of the reflected wave on gyrotron. In the numerical simulation of multimode gyrotron frequency locking by an external monochromatic signal, this approximation allows us to study several modes competition, including non-equidistant modes, the frequency distance between which can be comparable with the cyclotron absorption linewidth. Numerical simulation of the external signal and the reflected wave influence on gyrotron regime is carried out at the example megawatt gyrotron with an operating frequency 170 GHz. The regions where the operating mode is generated at the frequency of the external signal (lock-in zones), for a multimode gyrotron were founded. It is shown, that in lock-in regime multi-mode gyrotron can achieve higher efficiencies and operation frequency tuning increases by several times compared to free gyrotron. The scenario of electron beam parameters variation was similar with the real one, used to build up the high-efficiency generation in the gyrotron. Under the influence of the reflected wave gyrotron oscillation frequency can be kept within a narrow band, equal for the non-resonant reflector to the distance between modes of long delay line, and for high-resonant reflector - band external cavity. The cavity eigen-frequency of gyrotron can be varied in a much wider range of 5-6 times the range of variation of the frequency of radiation. The results permit us to conclude that the influence of external monochromatic or narrow- band reflected wave is an attractive method for frequency stabilization of gyrotron.