Transverse coupled bunch instabilities in low-energy injection storage rings

Abstract

The normal-conducting accelerating ring (NAR) is a synchrotron radiation source that uses a low-energy (15 MeV) injection scheme. This paper shows that a transverse coupled bunch instability occurs in NAR just after injection and that this instability limits the amount of current that can be stored. At such a low energy, the bunch length remains long because of the long radiation damping time. Sacheler's theory shows that the bunch length is so long that small changes in chromaticity produce a large effect on the form factor and thus on the growth rate of the instability. This chromaticity dependence of transverse coupled bunch instability has been observed experimentally in NAR.