The Concept of a Gyrotron with Megawatt Output at Both First and Second Cyclotron Harmonics for Plasma Heating in Spherical Tokamaks

Based on the analysis of electron–wave interaction, we study the possibility of developing a gyrotron that is able to provide a megawatt output power in quasi-continuous (long-pulse) oscillations at both first and second gyrofrequency harmonics. For selective excitation at the second cyclotron harmonic when the operating current is significantly higher than its starting value, we propose to lock the gyrotron by a weak (several percent power) monochromatic incoming signal which suppresses spurious oscillations at the fundamental cyclotron resonance in the gyrotron start-up process. Simulations of a two-frequency gyrotron with an output power of 1 MW at the first cyclotron harmonic (19 GHz) and 0.8 MW at the second one (38 GHz) based on a nonstationary self-consistent system of equations are presented. Such a source of radiation is of interest for plasma-heating systems in spherical tokamaks.