Numerical Studies on the Influence of Cavity Thermal Expansion on the Performance of a High-Power Gyrotron

An iterative procedure is described, which models the influence of the thermal expansion of the gyrotron cavity on the expected gyrotron performance. It is a multiphysics simulation method, which involves electrodynamic, thermal-hydraulic, and thermo-mechanical simulations. The method is applied to the first European 170-GHz, 1-MW continuous wave prototype gyrotron for the ITER. According to the simulations, a performance reduction of 15% is expected at nominal operating parameters, because of the thermal expansion of the cavity. Alternative operating points to mitigate this effect are proposed and numerically validated. The numerical results are discussed in light of experimental findings.