Control of coupled-bunch instabilities in high-current storage rings

Intense particle beams may be subject to coupled-bunch instabilities that would grow at rates greater than the bunch oscillation frequencies. The suppression of this growth requires both reduction of the driving impedances and active feedback of bunch motions. The shunt impedances of higher-order cavity resonances can be reduced by passive dampers and the beam impedance within the band of the fundamental resonance can be reduced by rf feedback around the cavity and power amplifier. The feedback of bunch motions composed of numerous coupled-bunch modes requires broad-band systems for which the amplifiers are costly. Examples proposed for electron storage rings are presented