Bench Measurements of the Loss Impedance for PEP Beam Line Components

Abstract

Bench measurements of the parasitic model loss parameter k, due to the interaction of a bunched beam with discontinuities in the vacuum pipe, are presented for many of the PEP beamline components. The measurements were made using the pulsed, coaxial transmission method of Sands and Rees. Full-scale machined and sheet metal models containing tapers, gaps, tanks (cavities), collimators, plates, electrodes and other irregular shapes were investigated. Accuracies, errors and modeling difficulties are pointed out. Loss curves and rules of thumb are discussed that should aid in the design of similar components. Also described is a moderately successful effort to de-Q some of the resonances in a particularly complicated chamber (separating plates) with a strip line coupling loop that is externally terminated at both ends.