Fast transverse instability in the NSNS Accumulator Ring

This paper reports on the results of investigation of possible fast transverse instabilities in the NSNS Accumulator Ring. The instability may be caused by the presence of stripline devices like kicker magnets, the active damper system, and by the RF cavities, and the sharp steps of the vacuum pipe. The instability can be overcome by adopting aluminum as the material of the vacuum chamber, and by smoothing the shape of the vacuum pipe. Still the growth time of the instability remains short especially for the mode in proximity of the betatron tune.