High Intensity Beam Instabilities in the Brookhaven AGS

Transverse resistive wall instabilities and longitudinal reactive wall instabilities have both been observed in the Brookhaven AGS. Recently an instability has been observed characterized by individual coherent phase oscillations of the twelve beam bunches. This instability is believed to be caused by high frequency resonance modes in the rf cavities introduced by recent modifications. A simple analysis shows that voltages induced in these parasitic resonances by the beam can couple the phase oscillations of the individual bunches. A normal mode analysis of the system predicts unstable normal modes with properties similar to the observations. Modifications to the rf cavities to suppress these undesirable effects have been devised.