An FPGA-based bunch-to-bunch feedback system at the Advanced Photon Source

The advanced photon source storage ring has several bunch fill patterns for user operation. The hybrids fill pattern consists of a single bunch with a charge of 16 mA and a bunch train of 56 bunches. Both horizontal and vertical instabilities are observed. Currently chromaticity correction is the only method available to overcome the instability. Beam lifetime and injection efficiency suffer because of high sextupole currents. A bunch-to-bunch feedback system is designed to overcome beam instability and reduce the required chromaticity correction. The feedback system is based on an FPGA DSP processor. The signal filtering algorithm is based on the time-domain-least-square (TDLF) method developed at SPring-8. We have just completed the integration of the system. We report the system design and some test results.