Digital Closed Orbit Feedback System for the
Advanced Photon Source Storage Ring

* Y. Chung, D. Barr, G. Decker, J. Galayda,
F. Lenkszus, A. Lumpking and A. J. Votaw
Argonne National Laboratory


The closed orbit feedback system for the Advanced Photon Source (APS) storage ring employs unified global and local feedback systems for stabilization of particle and photon beams based on digital signal processing (DSP). Hardware and software aspects of the system will be described in this paper. In particular, we will discuss global and local orbit feedback algorithms, PID (proportional, integral and derivative) control algorithm, application of digital signal processing to compensation for vacuum chamber eddy current effect, resolution of the interaction between global and local systems through decoupling, self-correction of the local bump closure error, user interface through EPICS, and system performance in the frequency and time domains. The system hardware including the DSPs is distributed in 20 VME crates around the ring, and the entire feedback system runs synchronously at 4 kHz sampling frequency in order to achieve the correction bandwidth exceeding 100 Hz. The required data sharing between the global and local feedback systems is facilitated via the use of fiber-optically networked reflective memories.

*Work supported by the U.S. Department of Energy, Office of Basic
Energy Sciences, under Contract No. W-31-109-ENG-38.