Change of Eigenstate in a Superconducting rf Cavity Due to a Nonlinear Response

Abstract

The studies on superconducting rf cavities have shown phenomena not familiar to normal conducting cavities. Therefore we rediscuss the phenomenological description of rf cavities at low‐ and high‐field levels, especially nonlinear effects accompanied with high rf field strength. To handle nonlinear effects an appropriate perturbation theory is developed. Together with knowledge on the surface impedance in the superconducting state and on field‐emitted electrons in the cavity this theory is solved in lowest approximation. The resulting frequency shift and the nonlinear rf losses are compared with published experimental data. This comparison shows that at present nonideal effects define the results. The intrinsic fast superconducting mechanisms causing harmonics are overshadowed by slow nonideal effects.