Impedance calculations for 2-D and 3-D structures and the impedance budget of 7-GeV APS storage ring

Abstract

The longitudinal and transverse coupling impedances of various kinds of two- and three-dimensional structures are calculated numerically for the storage ring of the 7-GeV Advanced Photon Source (APS). It is shown that the RF cavities are the main contributors to the longitudinal impedance, whereas the transitions between the chamber and the insertion device section dominate the transverse impedances. Several different numerical approaches are adopted. It is argued that the broadband resonator model may not be appropriate for modeling the longitudinal impedance. Several interesting phenomena of general interest, including a composition rule and the negative transverse impedance, are discussed. The present results and other results available are used to establish the impedance budget of the storage ring. >