Control and measurements of longitudinal coupled-bunch instabilities in the ATF damping ring

Damping ring at the Accelerator Test Facility (ATF) is a storage ring with 714 MHz RF frequency and harmonic number of 330. The ring is used in both single and multi- bunch regimes. In both cases, significant longitudinal dipole motion has been observed in the ring. A prototype longitudinal feedback channel using a Gproto baseband processing channel and a set of horizontal striplines has been constructed for the machine. The prototype allowed both suppression of the longitudinal motion and studies of the motion sources. In this paper, we present the results of these studies including measurements of steady-state oscillation amplitudes, eigenmodal patterns, and growth and damping rates. Using measured growth rates we estimate the driving impedances. We also present the effect of the longitudinal stabilization on the energy spread of the extracted beam as documented by a screen monitor.