Commissioning of the APS real-time orbit feedback system

Abstract

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 ...

Symmetry Exploitation in Orbit Feedback Systems of Synchrotron Storage Rings

“…When R is both BC and CS, the matrices R as well as R can be further decomposed. For the decomposition of R, we start by rewriting the complex-valued blocks of the BC decomposition R using (8) as…”

“…Most orbit feedback systems use a singular value decomposition (SVD) of R to synthesize an orbit controller, such as in [5] for the European Synchrotron Radiation Facility, [6] for Diamond Light Source, [7] for the MAX IV synchrotron or [8] for the Advanced Photon Source. In these case, the control input is calculated from u(z −1 ) = −Kc(z −1 )y(z −1 ), where c(z −1 ) is a scalar transfer function that accounts for the dynamics g(z −1 ), and the gain matrix K is calculated from [9, eq.…”

Real-time orbit feedback at the APS

“…Each contains interfaces to 16 rf BPMs and 16 corrector magnet power supplies in each plane (3). Every slave crate also contains digital signal processors (DSPs) that implement the real-time algorithms.…”

Tuning the narrow-band beam position monitor sampling clock to remove the aliasing errors in APS storage ring orbit measurements

“…In order to stabilize the beam orbit in the band up to 50 Hz, the Advanced Photon Source (APS) storage ring uses a real-time orbit feedback system [1]. This system uses up to 142 Nbbpms in the global correction algorithm with update rate at 1.53 kHz.…”