ANALYSIS OF METHODS FOR CONTROLLING MULTIBUNCH INSTABILITIES IN DA-PHI-NE

The e(-)e(+) DA Phi NE collider is designed to reach a luminosity of t he order of 10(32)-10(33) sec(-1) cm(-2) at 510 MeV, by storing high c urrent. Such a current, few amperes per beam, can in principle be achi eved by filling many RF buckets in the machine. One of the main beam d ynamics problems concerns the multibunch instabilities caused by the s trong coupling between the beam and the parasitic higher-order mode (H OM) resonances of the RF cavity. Due to the high current, the instabil ity is very fast, so it is impossible to stabilize the beam with a fee dback system alone. An effort has to be made to reduce the shunt imped ance of the cavity HOMs so that a feedback system can be effective. Th is task is accomplished by properly designing the RF cavity and by cou pling out the HOMs through loops or wave-guides to extract energy from the resonant fields, thus reducing at the same time the quality facto r e and the shunt impedance R. The residual excitation of beam oscilla tions is damped by a bunch-by-bunch digital feedback system.