ANL, Argonne
The Advanced Photon Source (APS) monopulse beam position monitor (BPM) system, designed to measure single- and multi-turn beam positions, is one of three BPM systems currently in use to measure and control both AC and DC orbit motions. Recently, one sector of the monopulse BPM system was upgraded by replacing its ca 1992 12-bit signal conditioning and digitizing unit (SCDU) with a field-programmable gate array (FPGA)-based system for signal processing. The system is comprised of a repackaging of the broadband rf receiver modules together with a VME Extensions for Instrumentation (VXI) module housing eight 14-bit digitizers and one FGPA. The system will be described in detail, including an overview of its new functionality, and performance will be discussed. Of particular interest is the noise floor, which will be contrasted with the previous system and with other systems in use at the APS.
ANL, Argonne
A cw tune measurement system for the IPNS RCS is described. The pinger magnets are energized by a solid-state, transformer-coupled power supply operating at 30 Hz. In its present configuration, the power supply provides a 160-A pulse to a pair of series-connected, single-turn ferrite magnets. The magnet pair drive separately x- and y-plane orbit bumps in the h=1 beam. The dipole oscillations generated in the beam are sensed with pairs of split-can, "pie" electrodes. Raw signals from the H and V electrodes are carried on matched coax-cables to 0/180-degree combiners. The output difference signals are recorded with gated spectrum analyzers. Bunch circulation frequency varies from 2.21 MHz at injection to 5.14 MHz at extraction. With a fixed frequency span of 24 MHz, between 4 and 10 bunch harmonics and sidebands (SBs) are present in the difference spectra. Software has been developed to use the multi-harmonic SBs present over the span to improve the accuracy of the tune measurements. The software first identifies and then fits the multiple SBs to determine the tune. Sweeping the beam across the momentum aperture provides a method for measuring the chromaticity.
SOLEIL, Gif-sur-Yvette
The Soleil Fast Orbit Feedback System has been integrated in the BPM electronics, using the FPGA resources of the Libera modules. On top of their position measurement, the FPGAs compute the orbit correction and drive the power-supplies of the 48 dedicated air coil correctors. Position data are distributed all over the ring by a dedicated network connecting the 120 BPMs modules together. The correction rate is 10 kHz and is applied with low latency. At almost all the source points, the high frequency stability specifications have already been achieved thanks to great care in the design of the machine. Remaining vibrations are still observed in the 46-54 Hz band and during the change in gap and phase of some insertion devices. Those perturbations are efficiently damped by the fast orbit feedback system. The BPM system has been operational for some time. The fast orbit feedback system is in its commissioning phase. The design and first results of the latter are reported.
CERN, Geneva
Field Programmable Gate Arrays (FPGAs) have become a central enabling technology for the design of fast digital signal processing systems. This tutorial starts with an introduction to digital signal processing and a comparison with analog techniques. We then treat the problem of choosing between the two key technologies for digital systems: Digital Signal Processors (DSPs) and FPGAs. Once the advantages of FPGAs for very demanding systems have been laid out, we go on with a survey of digital design techniques of general nature, followed by tips and tricks more directly applicable to FPGA implementations. Digital signal processing in FPGAs typically uses a fixed-point number representation. We explain how different fixed-point arithmetic operations can be implemented, and the trade-offs regarding speed, silicon area and precision. Finally, all the concepts are applied to a set of examples in beam instrumentation.