Chromaticity for energy spread measurement and for cure of transverse multi-bunch instability in the SPring-8 storage ring

Chromaticity of a ring introduces non-harmonic betatron motion to off-momentum electrons. This motion produces synchrotron sidebands of betatron frequency in frequency, response of betatron motion of a beam and reduces the main peak height. The height of these peaks depends,on chromaticity and on the energy spread of the beam and we measured energy spread of the SPring-8 storage ring. The reduction of the main peak works to reduce the strength of instabilities and we suppress the horizontal coupled-bunch instability driven by cavity higher order modes and the vertical coupled-bunch instability driven by resistive-wall impedance of the in-vacuum type insertion devices by introducing horizontal and vertical chromaticity 7 and 6, respectively. These chromaticity reduce the strength of these instabilities to half of those at zero chromaticity