A unified global and local closed-orbit feedback system has been implemented at the Advanced Photon Source in order to stabilize both particle and photon beams. Beam stability requirements in the band up to 50Hz are 1 7~ in the horizontal plane and 4.4pm vertically. Orbit feedback algorithms are implemented digitally using multiple digital signal processors, with computing power distributed in 20 VME crates around the storage ring. Each crate communicates with all others via a fast reflective memory network. The system has access to 320 rf beam position monitors together with x-ray beam position monitors in both insertion device and bending magnet beamlines. Up to 3 17 corrector magnets are available to the system. The global system reduces horizontal ms beam motion at the x-ray source points by more than a factor of two in the frequency band from lOmHz to 50Hz. SYSTEM DESCRIPTION I . I Hardware ArchitectureThe real-time orbit feedback system is implemented digitally using multiple digital signal processors (DSPs). A total of twenty VME crates are distributed around the circumference of the 40-sector APS storage ring to manage interfaces to beam position monitors (BPMs) and correctors, and to compute orbit corrections. Sofrware ArchitectureThe 68040 EPICS processor interfaces the DSP(s) to the control system and provides the means to monitor and control feedback algorithms running on the DSP. Data structures residing in dual-ported RAM on the DSP board are used to communicate commands and return status and data. The EPICS processor uses state programs to interface database variables with the shared data structures.The reflective memories contain a shared data structure that is replicated at each node and is accessible to all processors in the feedback system. At each sample tic the DSP fetches BPM data from the BPM interfaces, computes the error in position, and writes the error values to assigned locations in the reflective-memory shared data structure. When all other DSPs have written their BPM errors, the DSP reads in the complete BPM error vector from the reflective memory and computes and writes new corrector values.The master feedback crate provides global controls to the other 20 feedback crates by writing to specific locations in the reflective-memory shared data structure. In addition, it provides analysis tools such as 'dspscope' which functions like a digital scope, and 'ac voltmeter' which performs a sliding discrete Fourier transform in real time, both tools working on 40 channels of data. RF Beam Position MonitorsThe APS storage ring contains 360 rf BPMs, of which 320 are available to the real-time feedback system. In order to improve spatial resolution and minimize measurement error, it is preferable to use as many of the available BPMs as possible in the global correction algorithm. However computational resources are limited, and t h e n is a r of BPMs in the lkHz [l]. X-ray Beam Position MonitorsIn addition to the rf BPMs, the APS is implementing x-ray BPMs on all the insertion device ...

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The Advanced Photon Source (APS) is a thirdgeneration synchrotron light source in its tenth year of operation. The storage ring employs three different types of beam position monitor (BPM) systems to measure and control beam motion. The monopulse radio frequency (rf) BPM is a broadband (10-MHz) system, which is considered to be the backbone of orbit control. The rf BPM system was designed to measure single-turn and multi-turn beam positions.The rf BPMs are presently suffering from an aging data acquisition system. By replacing only the data acquisition we will revitalize this system for another decade and demonstrate a cost-effective approach to improved beam stability, reliability, and enhanced postmortem capabilities. In this paper we present the design of an eight-channel ADC/digitizer VXI board with a sampling rate of 88 MHz (per channel) and 14-bit resolution coupled with a field-programmable gate array and embedded signal processing. We will discuss the upgrade system specifications, design, and prototype test results.

A Cerenkov radiation detection system has been designed for Argonne National Laboratory's Advanced Photon Source 7-GeV electron storage ring. This system is intended for monitoring and measuring localized beam losses. The Cerenkov radiation detection system includes a detector assembly mounted at selected locations in the storage ring tunnel and an electronics package in a VME format. The electronics package consists of a high-voltage power supply, a 16-bit pulse discriminator-counter, two gated integrators, and two 16-bit analog-to-digital converters. The design of the timing circuit offers an extended range of 655 µs for both the gated integrator gate width and gate delay. The detectors have been installed near all storage ring scrapers, the storage ring thin-septum magnet, and at several insertion device locations. Plans are to instrument all present and future insertion devices. This paper discusses the electronics design as well as the mechanical design of the Cerenkov detector system.