Collective beam instabilities in the Taiwan Light Source

The storage ring at Taiwan Light Source has experienced a strong collective instability since 1994. Various cures have been attempted to suppress this instability, including the use of damping antenna, tunable RF plungers, different filling patterns, and RF gap voltage modulation. So far these cures have improved the beam intensity, but the operation remains to be limited by the instability. The dominant phenomenon is the longitudinal coupled bunch instability. The major source of longitudinal impedance is from RF cavities of Doris type. The high-order modes of the cavity were numerically analyzed using a 3-D code GdfidL. The correlation of the observed phenomenon in user operation with high-order modes of RF cavities will be presented. Results of various attempts to suppress beam instabilities will be summarized. Proposed cures for beam instabilities will be discussed