Longitudinal feedback system for the Photon Factory

In the KEK Photon Factory, longitudinal coupled- bunch instabilities are suppressed using the RF phase- modulation technique during the users operation. This technique is very effective not only to suppress the instabilities but also to enlarge the beam lifetime. Together with the study for top-up operation, longitudinal bunch-by-bunch feedback system has been developed. A two-port longitudinal kicker based on DAPhiNE-type cavity were designed and installed in the storage ring in the summer of 2006. FPGA-based signal processing part is under development based on the KEKB design. A mode feedback system which suppresses a specific coupled-bunch mode was tested successfully as a preliminary test of the kicker. By using a commercial FPGA evaluation board, a simple bunch-by-bunch feedback system was implemented and succeeded to suppress the coupled-bunch instability up to 52 bunches in the ring.