Head-tail instability in the KEK-PS main ring

A horizontal head-tail instability has been observed at the beginning of acceleration in the KEK-PS main ring. The instability occurs due to a large change in chromaticity produced by the sextupole component of the eddy-current induced field in the dipole beam-pipe. The horizontal chromaticity increases up to a positive value around 80 ms after the beginning of acceleration. The longitudinal mode 0, 1 and 2 have been observed. The impedance model, including resistive wall impedance, kicker impedance and broad band impedance, explains the instability for a single bunch operation very well. (author)