Measurement and analysis of kHz orbit fluctuations in the Pohang Light Source

Abstract

In this article, we report on the orbit stability in the kHz frequency range of the Pohang Light Source (PLS). Fluctuations of the stored beam positions in the PLS storage ring were measured using a digital beam position monitor (BPM) at a fixed location in the ring. Fourier analysis of the measured beam position revealed fluctuation frequencies in the kHz range. The current ripples of the corrector magnet power supplies (MPSs) are suspected to be the sources of these position fluctuations. We surveyed the current ripples of 140 corrector MPSs in the ring to obtain their frequency distribution. The distribution, weighted by the response-matrix elements for each correctors and the BPM, was found to have a strong correlation with the spectrum of the beam-position fluctuations, which substantiates the suspicion.