Impedance analysis with longitudinal bunch-shape measurements

Abstract

We used a streak camera to measure the longitudinal bunch shape of a circulating electron beam in the 2.5-GeV Pohang Light Source (PLS). The measured results were analyzed by an (R+ L) series model to obtain a resistance R = 1.1 k Omega, an inductance L = 89 nH, and a longitudinal impedance vertical bar Z/n vertical bar(eff) = 0.6 Omega. The scaling law for the bunch lengthening is expressed as sigma(i) proportional to I-0.22 +/- (0.01). The effect of insertion device in the ring on the impedance, particularly the effect of the vertical height of the in-vacuum undulator currently placed in the PLS ring, is presented.