Interpretation of coupling impedance bench measurements

Abstract

Coupling impedance values of accelerator components can be obtained from standard bench measurements based on the coaxial wire method. Longitudinal impedance is obtained with one wire and the transverse impedance with a twin wire inserted into the “device under test.” The coupling impedance follows from the interpretation of the scattering coefficients from a network analyzer. In this paper, models and formulas applicable to the interpretation of the data are collected and reviewed. The paper is focused on lumped and distributed kicker magnets, for which a simulated measurement is numerically analyzed with the results graphically presented. This study suggests that the application of the standard lumped formula or the simple log formula for distributed impedances is appropriate.