Suppression of Coherent Synchrotron Oscillation of the Spring-8 Storage Ring

For the realisation of a highly brilliant photon beam in a third generation synchrotron radiation source such as SPring-8, it is very important to eliminate an orbital vibration of the stored electron beam. In the SPring-8 storage ring, coherent synchrotron oscillation with amplitude of 0.2mmp-p was observed by BPM located in a dispersive section. Since the energy oscillation amplitude is proportional to the product of the phase noise amplitude and the inverse of the momentum compaction factor, the energy oscillation amplitude is enhanced by low momentum compaction factor. To make the amplitude of this synchrotron oscillation as low as possible, we checked the performance of synthesiser by measuring the noise level around the synchrotron frequency, and selected a synthesiser with best performance. Furthermore, the remaining amplitude was corrected within about 1/10 by applying frequency modulation to the RF reference signal.