Analytic Modeling, Simulation and Interpretation of Broadband Beam Coupling Impedance Bench Measurements

TL;DR

This paper presents a comprehensive theoretical framework and experimental validation for broadband beam coupling impedance measurements, addressing systematic errors, material effects, and measurement optimization.

Contribution

It introduces a generalized approach to impedance measurements, compares conversion formulas, and analyzes error sources, enhancing accuracy and understanding of beam coupling impedance characterization.

Findings

Systematic measurement errors can be estimated and minimized.

Impedance dependence on relativistic velocity and material properties is characterized.

Measurement and simulation results show good agreement, validating the approach.

Abstract

In the first part of the paper a generalized theoretical approach towards beam coupling impedances and stretched-wire measurements is introduced. Applied to a circular symmetric setup, this approach allows to estimate the systematic measurement error due to the presence of the wire. Further, the interaction of the beam or the TEM wave, respectively, with dispersive material such as ferrite is discussed. The dependence of the obtained impedances on the relativistic velocity $\beta$ is investigated and found as material property dependent. The conversion formulas for the TEM scattering parameters from measurements to impedances are compared with each other and the analytical impedance solution. In the second part of the paper the measurements are compared to numerical simulations of wakefields and scattering parameters. In practice, the measurements have been performed for the circularly symmetric example setup. The optimization of the measurement process is discussed. The paper concludes with a summary of systematic and statistic error sources for impedance bench measurements and their diminishment strategy.