Study and Compensation of Coherent Longitudinal Instability in the CERN PS

Coherent longitudinal instabilities, similar to those observed in electron storage rings and in the Brookhaven AGS, occur in the CERN PS. The resulting dilution in longitudinal phase space would critically affect the luminosity obtainable in the intersecting storage rings (ISR). A theoretical study of the mechanism of this instability is presented, including the influence of the beam control loop. A compensation technique, based on introducing a difference in the synchrotron frequencies of different bunches has been studied. We find that in the presence of beam control the effectiveness of this cure depends critically on the pattern in which the frequency varies between the bunches.