Simulations and Calculations of Cavity-to-cavity Coupling for Elliptical SCRF Cavities in ESS

The proton linac of the European Spallation Source (ESS) will rely on two families of superconducting cavities for the medium and high beta regions. Presented here are simulations of various cavity designs for different betas. The simulations are performed using the ACE3P codes developed at SLAC National Accelerator Laboratory, and the simulated eigenmode and R/Q spectrum will be shown for each design. Dangerous modes are identified. Of particu- lar importance is the investigations of multiple cavity (cryomodule) configurations. From this, the simulated cavity- to-cavity coupling within a cryomodule is extracted. A the- oretical model of this coupling based on coupled potential wells in quantum mechanics has also been developed, and a comparison made with the results of the simulation.