Coupling impedances of a resistive insert in a vacuum chamber

Shobuda, Yoshihiro   ; Chin, Y. H.*; Takata, Koji*

We have developed a theory to calculate both longitudinal and transverse impedances of a resistive short (typically shorter than the chamber radius) insert with cylindrical symmetry, sandwiched by perfectly conductive chambers on both sides. It is found that unless the insert becomes extremely thin (typically a few nm for a metallic insert) the entire image current runs on the thin insert, even in the frequency range where the skin depth exceeds the insert thickness, and therefore the impedance increases drastically from the conventional resistive-wall impedance. In other words, the wake fields do not leak out of the insert unless it is extremely thin. Formulae of the impedance valid for various cases of the insert are categorized in summary.