Abstract:
Background The C-band photocathode electron gun is a key front-end device of the accelerator for the Southern Light Source Free-Electron Laser, whose resonant frequency stability is crucial for beam quality and long-term operation. During high-power microwave excitation, electromagnetic power loss on the inner surfaces of the resonant cavity produces non-uniform thermal loading, leading to structural deformation and subsequent resonant frequency drift, which cannot be accurately characterized by traditional single-physical-field analyses.
Purpose To clarify the intrinsic mechanism of this phenomenon, a comprehensive electromagnetic–thermal–structural multi-physical field coupling model is developed based on the COMSOL Multiphysics® simulation platform.
Methods First, high-frequency electromagnetic simulations are carried out to obtain the designed resonant frequency of the vacuum cavity at 5.712 GHz and to calculate the surface electromagnetic loss power density. Based on these results, an equivalent boundary heat source model is established. Combined with the external mechanical structure and cooling pipline model of the electron gun, the non-uniform temperature distribution of the cavity under realistic cooling conditions is obtained by employing a fluid–solid coupling method. Subsequently, the solid mechanics interface is used to compute the thermally induced deformation of the cavity geometry, and the deformed structure is introduced into a secondary high-frequency simulation to evaluate the resulting resonant frequency drift.
Results The results reveal a clear transmission path from microwave power loading to temperature rise, structural deformation, and frequency shift, quantitatively demonstrating the strong coupling among electromagnetic, thermal, and mechanical fields.
Conclusions This study realizes a complete multi-physical field coupling analysis of the C-band photocathode electron gun and provides an effective numerical framework for predicting resonant frequency drift, offering important guidance for the thermal–mechanical coupling design and frequency stability optimization of high-precision microwave cavities.
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