Study of Longitudinal Coupled-bunch Instabilities in the Srrc Storage Ring

Longitudinal coupled-bunch instabilities in the SRRC 1.3 GeV storage ring have been studied by analyzing the signals picked up from the stripline electrodes and rf power reflected from the cavities. The current dependence of the instability strengths was measured. As a cross check, the bunch phase jitters as a function of beam current has also been measured by using sampling optical oscilloscope. Threshold currents of a few milliamperes have been determined from both measurements. They agree with each other very well. It is also found that the strength of the instabilities can be reduced significantly by randomly distributing electron bunches around the ring.