Frequency locking of a megawatt-class gyrotron accounting for spectrum broadening by voltage instabilities

This paper presents a theoretical study on the frequency locking of a high-power gyrotron by an external signal based on a time-dependent self-consistent model that accounts for electron energy fluctuations driven by voltage instabilities in the high-voltage power supply. To enable long-term interaction modeling, a highly efficient computational algorithm is proposed to accelerate the simulations. Analysis is performed for a megawatt-class, 170 GHz gyrotron, for which the experimental data are available both for free-running and frequency-locking regimes. The calculated free-running radiation spectrum linewidth, broadened by the given voltage fluctuations, is in close agreement with experimental results. The simulations with an external signal demonstrate that incorporating voltage fluctuations narrows the frequency-locking bandwidth by approximately 10% as compared to the case where this factor is neglected.