Local beam position feedback experiments on the ESRF storage ring

This paper describes the results of local beam position feedback experiments conducted on the ESRF storage ring using digital signal processing (DSP) under the trilateral agreement of collaboration among ESRF, APS, and SPring-8. Two RF beam position monitors (BPMs) in the upstream and downstream of the insertion device (ID) and two X-ray BPMs in the sixth cell were used to monitor the electron beam and the X-ray beam emitted from the ID, respectively. The local bump coefficients were obtained using the technique of singular value decomposition (SVD) on the global response matrix for the bump magnets and all the available BPMs outside the local bump. The local response matrix was then obtained between the two three-magnet bumps and the position monitors. The data sampling frequency was 4 kHz and a proportional, integral, and derivative (PID) controller was used. The result indicates the closed-loop feedback bandwidth close to 100 Hz and clear attenuation (≈-40 dB) of the 7-Hz beam motion due to girder vibration resonance. Comparison of the results using the RF BPMs and X-ray BPMs will be also discussed