Thermoanalysis and Its Effect on the Multimode Beam-Wave Interaction for a 0.24-THz, Megawatt-Class Gyrotron

The detailed analyses of heat transfer and its effect on the cold cavity, effective conductivity, and beam-wave interaction for a 0.24-THz megawatt-class gyrotron is presented in this paper. In the heat transfer analysis, the commercial finite-element method software ANSYS was used, in which Fluent was selected to simulate the thermal analysis, and Static Structural was selected to simulate cavity mechanics. For the cavity cooling system, 50 uniform axial wedge grooves in the outside surface of the cavity were considered, in which the total external loaded coolant flow rate is 40 L/min. The thermal analysis result shows that the maximum temperature is about 260 °C in the center section of the cavity. The deformed cavity was obtained by the structural analysis. After ANSYS simulation, the cold and the hot cavities with deformation were simulated by the in-house developed time-dependent, self-consistent multimode interaction code, in which the distributed conductivity caused by the distributed temperature was used. For the cold cavity, the electric field profile is not changed significantly, but the diffraction quality factor and resonant frequency are reduced by 60 and 0.191 GHz, respectively. The output power is not changed seriously, but the oscillation frequency is decreased by 0.18 GHz.