Analysis of coupled-bunch instabilities in Diamond-II

The low-frequency components of the impedance drive coupled-bunch instabilities in electron synchrotrons. In the Diamond-II storage ring, the geometric component of the impedance of some vacuum vessels is comparable in strength to the resistive-wall impedance. This study compares the growth rates of all coupled-bunch modes obtained through simulations and analytical calculations. Self-consistent simulations, incorporating the harmonic cavity along with short-range wakefields and higher-order cavity modes, show that the beam can be stabilised with and without multi-bunch feedback by adjusting the chromaticity.