The e+e- DAPHNE collider is designed to reach a luminosity of the order of 10³2-10³3sec^-1 cm^-2 at 510 MeV, by storing high current. Such a current, of the order of few amperes for beam, can in principle be achieved by filling many RF buckets in the machine. One of the main problems arising in the beam dynamics concerns the Multibunch Instabilities caused by the strong coupling between the beam and the parasitic HOM resonances of the RF cavity. Due to the high current, the instability is very fast, so that it is impossible to stabilize the beam with a feedback system alone. An effort has to made to reduce the shunt impedance of the cavity HOMs, so that a feedback system can be effective. This task is accomplished by properly designing the RF cavity and by coupling off the HOMs through loops or waveguides in order to extract energy from the resonant fields, thus reducing at the same time the quality factor Q and the shunt impedance R. The residual excitation of beam oscillations is damped by means of a bunch-by-bunch digital feedback system.
S. et al. (1993) studied this question.