Investigations of Bunch Filling Patterns to Suppress the Longitudinal Coupled-Bunch Instability at the Pohang Light Source

Abstract

A longitudinal coupled-bunch instability may be generated at the 2.5 GeV Pohang Light Source (PLS), depending on the parameters of the rf system and the machine parameters of the storage ring. In the near future, one more rf cavity will be inserted into the storage ring to raise stored beam current. Then, the performance of the storage ring may be limited by the longitudinal coupled-bunch instability due to the higher-order modes in the rf cavities as the beam current increases. Accordingly, in order to suppress the longitudinal coupled-bunch instability, the dependence of the longitudinal coupled-bunch instability in the higher beam current on the bunch filling patterns in the ring were intensively investigated by using a simulation method. Our simulation shows that the beam energy spread due to the longitudinal coupled-bunch instability in the ring can be suppressed by choosing optimal bunch filling patterns with empty buckets between bunches and gap buckets.