Research and development of the longitudinal feedback system digital signal processing electronics in BEPCII

The current strategy to achieve high luminosity for high energy physics experiments is to store huge currents distributed in many bunches in circular machines such as BEPCII, so the longitudinal coupled bunch instabilities of the beam are inevitable. Therefore, a longitudinal feedback system is needed to suppress longitudinal oscillation. Otherwise, the beam energy spread will increase; the luminosity and the beam lifetime will decrease under a certain beam current. For filter design of the feedback system, the time domain least square fitting (TDLSF) method is compared to the selective wave filter method; digital signal processing electronics based on commercial board have been developed and tested on BEPCII. The final result shows that the self-developed longitudinal feedback system can suppress the longitudinal beam oscillation at 750 mA beam current and meet the requirements of BEPCII; the restrain depth to the sidebands reaches to 40.8 dB.