The rapid cycling synchrotron (RCS) requires the magnetic field to track the energy ramp, producing a strongly time-dependent magnetic environment. To control beam coupling impedance and suppress field leakage, an RCS typically uses ceramic vacuum chambers covered with an RF shielding layer. The shield consists of parallel metal strips aligned with the beam and terminated by capacitors at either end, which preserves a low beam impedance while suppressing eddy currents induced by the time-dependent magnetic field. Previous theoretical studies suggest that the impedance of such a structure has a negligible impact on the beam. However, impedance measurements of the China Spallation Neutron Source RCS ceramic chamber have revealed the presence of a transverse resonant impedance.

The purpose of this study is to investigate this observation, which has not been verified by independent methods.

The CST electromagnetic simulations are used to test its presence.

A high-fidelity simulation model has been developed and benchmarked against measurements, showing close agreement with the measured impedance.

The comparison confirms the validity of the impedance characterization. Simulations spanning six ceramic chamber geometries are then used to construct a comprehensive impedance model for the RCS, which provides a foundation for subsequent studies of beam dynamics and collective effects.