Generalization of coupled S-parameter calculation to compute beam impedances in particle accelerators

Abstract

In this article, a decomposition approach for the computation of beam coupling impedances is proposed. This approach can account for the mutual electromagnetic coupling in long accelerator structures consisting of several consecutive segments. The method is based on the description of the individual segments using a multimodal network matrix formulation in which the charged particle beam is considered as an additional port. Then, the generalized multimodal network matrices of all segments are combined to a multimodal network matrix of the complete structure. The beam coupling impedance as well as the scattering parameters of the full structure are recovered as particular matrix elements in this multimodal network matrix. The new method generalizes Coupled S-Parameter Calculation (CSC) introduced in earlier work such that charged particle beams are considered. Consequently, the introduced scheme is referred to as CSC. Application examples for realistic accelerator components such as the simulation of a full TESLA 1.3 GHz-cavity of the European XFEL are provided. These simulations demonstrate the high accuracy and numerical performance of the proposed method.