Orbit stability and feedback control in synchrotron radiation rings

Stability of the electron orbit is essential for the utilization of a low-emittance storage ring as a high-brightness radiation source. The development of the measurement and feedback control of the closed orbit is discussed, with emphasis on the activities at the National Synchrotron Light Source of Brookhaven National Laboratory. The author discusses the performance of the beam position detectors in use and under development: the PUE RF detector, the split ion chamber detector, the photoemission detector, the solid-state detector, and the graphite detector. Depending on the specific experiments, different beamlines require different tolerances on the orbit motion. Corresponding to these different requirements, two approaches to closed orbit feedback are discussed: the global and local feedback systems. The author describes a scheme for real-time global feedback by implementing a feedback system based upon a harmonic analysis of both the orbit movements and the correction magnetic fields