A New Integrated Multi-Physics Simulation Tool for Gyrotron Cavity Performance Evaluation

High-power gyrotrons are essential for Electron Cyclotron Resonance Heating (ECRH) in nuclear fusion devices, but face significant operational challenges due to extreme cavity heat loads. In particular, thermal deformation of the resonant cavity alters the electromagnetic mode dynamics, often leading to mode loss and instabilities. To tackle this limitation, we developed a fully integrated multiphysics simulation platform that iteratively couples our in-house time-dependent, self-consistent interaction code, ROCK, with thermo-hydraulic and thermo-mechanical model in COMSOL Multiphysics®. This robust framework is capable of assessing electromagnetic performance under varying cavity geometries, operating conditions, and cooling system designs. The approach was validated by benchmarking against the established simulation tool for the 170 GHz ITER gyrotron, showing excellent qualitative agreement and quantitative deviations within 10%. Applying the methodology to an optimized cooling system design revealed a significant reduction in thermal deformation and the corresponding frequency drop—key factors for stable gyrotron operation. These results confirm that the integrated approach can effectively guide gyrotron cavity designs for a wide range of fusion applications, including systems for W7-X and next-generation fusion devices such as DEMO.