Theory and Simulations of Frequency-locking Operation of a MW-level Gyrotron

This report contains the theoretical analysis of frequency-locked gyrotron operation based on developed time-domain multi-mode model with self-consistent axial structure of RF fields, which provides more adequate description of high-power gyrotrons with low-Q resonators. In the frame of this approach, the evolution of modes’ amplitudes is described by non-uniform parabolic equations supplemented by integro-differential boundary conditions which take into account the input of an external signal from the collector edge of the gyrotron resonator. We present the results of simulations of the last experiments with a 170-GHz ITER gyrotron, analyzing both the continuous-wave free-running generation and the frequency-locked operation and beating regimes in the presence of an external signal from a low-power gyrotron-driver. The locking band, output power and efficiency are calculated, as well as radiation spectra for different operating conditions. Simulations results are in fine agreement with experimental data.