Suppression of beam instabilities induced by accelerating cavities

A requirement for electron storage rings for the synchrotron radiation experiments is that circulating beam is very stable. In particular, for small emittance machines, obtaining a high-quality beam is the most important subject. Though the rf-accelerating cavities are essential for the storage rings, sometimes they cause serious beam instabilities, and lead to a current limit and an emittance growth. The Photon Factory storage ring (KEK) is a dedicated synchrotron radiation source. There are four single-cell cavities in the ring. Beam instabilities arising from the cavities have been investigated. The resonant frequencies of these cavities were trimmed by choosing the proper length of blank-flanges attached to the cavity ports, to avoid the conditions unstable for all existing coupled-bunch instabilities. Reduction of the instabilities was remarkable.