Multiphysics Pretuning Simulation and Testing of a Prototype 1.5-GHz SRF Cavity

Pre-tuning is one of the main processes during production of a superconducting radio-frequency cavity. Instead of the traditional tuning process in air, we investigate in this study cavity tuning under vacuum. As a test, two elliptical 1.5-GHz cavities are characterized on a tuning station and compared with a finite-element simulation to investigate the tuning mechanism. The cavity must be axially loaded for elastoplastic deformation during the pretuning process and therefore, both the incremental computation and the kinematic-hardening are included to describe the elastoplastic behavior of the deformed cavity. An effective simulation process is applied to the multiphysics computation so that the electromagnetic resonance frequency of a highly deformed cavity can be successfully predicted. Test results on 1.5-GHz copper cavities verify the multiphysics computational results. Both test and numerical results show that the tuned frequency is almost linearly dependent on the residual longitudinal displacement.