Direct Observation of the Fast Beam-Ion Instability

Abstract

Direct evidence of the fast beam-ion instability (FBII) was obtained in the Pohang Light Source by measuring the bunch-by-bunch parameters from the snapshots of the beam image. With the direct observation, we confirmed the FBII signals and clarified uncertainties of the blowup factors quantitatively: bunch size blowup of $\ensuremath{\sim}2{\ensuremath{\sigma}}_{y}$ and the oscillation amplitude of $\ensuremath{\sim}0.75{\ensuremath{\sigma}}_{y}$. Suppression of the FBII was also demonstrated in the presence of the multiple gases or an extra clearing gap in the bunch train.