Longitudinal coupled bunch instabilities on the NSLS X-ray ring

Studies have demonstrated that an 862 MHz RF cavity higher order mode (HOM) causes longitudinal coupled-bunch (LCB) dipole and quadrupole oscillations at specific RF tuner positions with associated increases in longitudinal, horizontal, and vertical electron beam sizes. In the XRF2 cavity a reconfiguration of damping antennae removed the 862 MHz HOM. High speed I(t) stripline measurements showed that a strong quadrupole oscillation resulted when the HOM was induced in the XRF3 cavity. The reason that a symmetric six bunch pattern was found to be effective in damping this mode is explained.