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 BEAM. 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.

Numerical Analysis of a Single-Stage Fast Linear Transformer Driver Using Field-Circuit Coupled Time-Domain Finite Integration Theory

“…During the design and prototyping of FLTD, it is necessary to investigate self-consistent electromagnetic (EM) fields by using numerical approaches. FLTD and Z-pinch related simulations are usually performed with equivalent circuit model [8][9][10][11][12], finite-difference time-domain (FDTD) method [13][14][15], finite element method (FEM) [16][17][18][19][20], and partial element equivalent circuit (PEEC) method [21][22][23], etc. Koval'chuk et al [8] proposed the concept of linear transformer driver (LTD) as a fast primary energy storage device for the first time and validated its output performance.…”

“…Gourdain et al [19] analyzed geometries of nested transmission lines in the FLTD driven accelerator using the RF module of FEM software COMSOL. Flisgen et al [20] implemented frequency domain higher-order FEM to determine the generalized scattering matrices of a long accelerator structure. FEM is suitable for modeling complex structures and media distributions [25]; nevertheless, it has low calculation speed and high memory consumption [26].…”