IHEP Beijing, Beijing
As the upgrade project of Beijing Electron Positron Collider (BEPC), BEPCII will still serve both high energy physics experiments and synchrotron radiation applications. The storage ring of BEPCII consists of electron ring (BER), positron ring (BPR) and synchrotron radiation ring (BSR). Up to now, we have completed two stages run. The first stage run started on Nov. 13, 2006 by using conventional magnets instead of superconducting (SC) magnets in the interaction region (IR). The second stage operation started on Oct. 24, 2007 by using SC magnets and without BESIII detector. In this paper, we will present the progress of the BEPCII storage ring diagnostics system along with the BEPCII commissioning, such as how Libera BPM has been used for the BPR first turn measurement and the injection residual orbit research of BER; COD measurement can satisfy the resolution requirement for the beam-beam scan in the IR and for the slow orbit feedback; BCM can help us on the different injection pattern; and the TFB system is important to suppress the strong multibunch instabilities when the higher beam current run. The tune meters and the beam-loss monitors are also described in this paper.
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
There are two parallel feedback systems to correct the transverse orbit at the Advanced Photon Source (APS) storage ring: a real-time feedback system that runs at 1.5 kHz using 38 fast correctors and up to 160 beam position monitors (BPMs), and a DC feedback system that runs at 10 Hz using up to 317 correctors and over 500 BPMs. An algorithm that uses the open- and closed-loop beam motion data to spatially locate strong noise sources in the storage ring is described. A simulation code has been developed to predict the ideal closed-loop beam motion data from measured open-loop beam motion data assuming no steering corrector noise. With the difference between predicted and measured closed-loop beam motion data and the full inverse response matrix, we compute the source candidate locations and infer their relative strengths for narrowband sources. The simulation process and experimental results with beam will be presented.
LBNL, Berkeley, California
The Advanced Light Source Transverse Feedback System currently consists of a refrigerator sized analog delay line system. The new system is the 2nd generation Transverse Feedback System, derived from work done for PEP-II in 2004. It uses the latest generation Virtex-5 FPGA, and has 12-bit ADCs and DACs for bunch-bunch feedback at 500MHz. In addition, this system provides networked capability for setup and diagnostics.
LANL, Los Alamos, New Mexico
The LANSCE accelerator facility utilizes 110 wire scanner devices to monitor the accelerator's charged particle beam. The LANSCE facility's existing wire scanner control systems have remained relatively unchanged since the LANSCE accelerator became operational in the 1970's. The evolution of motion control technologies now permits the development of a wire scanner motion control system that improves in areas of energy efficiency, precision, speed, resolution, robustness, upgradeability, maintainability, and overall cost. The purpose of this project is to research the capabilities of today's motion control products and analyze the performance of these products when applied to a wire scanner beam profile measurement. This experiment's test bed consists of a PC running LabVIEW, a National Instruments motion controller, and a LEDA (Low Energy Demonstration Accelerator) actuator. From this experiment, feedback sensor performance and overall motion performance (with an emphasis on obtaining maximum scan speed) has been evaluated.
SLAC, Menlo Park, California
Bunched beam signals from button-style Beam-Position Monitor (BPM) electrodes can have spectral content up to 20-30 GHz and time-domain structure of narrow impulsive trains. Multi-bunch feedback systems require receivers to process such beam signals and generate ΔX, ΔY, and ΔZ beam motion signals. To realistically test these receivers, we have developed a 4-bunch programmable impulse generator, which mimics the signals from a multi-bunch beam. Based on step-recovering diode techniques, this simulator produces modulated 100-ps impulse signals. The programmable nature of the system allows us to mimic Betatron and Synchrotron signals from 4 independent bunches with adjustable beam spacing from 1 to 8 ns. Moreover, we can observe nonlinear effects and study the noise floor and the resolution of the receiver. This paper presents the design of the system and shows typical achieved results.
J. Xu, J.D. Fox, D. Van Winkle
Stanford Linear Accelerator Center
Stanford, CA 94309, U.S.A.
SLAC, Menlo Park, California
The Linac Coherent Light Source (LCLS) must deliver a high quality electron beam to the undulator. High resolution beam position monitoring is required to accomplish this task. Critical specifications are a dynamic range of 0.08-8.0 nC with a 5 microns resolution at 200 pC. New processor electronics was designed, processing is based on filtering the signals and direct digitization of the resulting pulse train. The processor consists of an Analog Front-End (AFE) and Analog-to-Digital Converter (ADC) boards, all are packed into 19-in rack mount chassis, 1U high. AFE board has a very low input noise, approximately 3 microV rms in a 7 MHz bandwidth centered at 140 or 200 MHz. The maximum gain is 34 dB with attenuation of up to 46 dB in 1 dB step. An on-board pulser sends the short CW burst to the striplines to perform between pulse calibration. The ADC board has four 16-bit digitizers, the sampling frequency is 120 MHz. The low-jitter clock is on a separate board in the same chassis. For the LCLS injector 22 prototypes of the processors were built and installed in 2007. Measured resolution at 200 pC is typically 3-5 microns. The 53 improved and modified processors are in production
CELLS-ALBA Synchrotron, Cerdanyola del Vallès
ALBA synchrotron light source is a 3rd generation light source being constructed by the CELLS consortium near Barcelona, Spain. Orbit correction system will be based on the Libera Brilliance electronics and its goal will be the stabilization of the beam at the submicron level. Important parameters to reach such corrections have been measured and are reported in this document, like electronics resolution, beam current dependence, latency (among others). Comparison of the two different Libera products offered by the company (Libera Electron and Libera Brilliance) is also reported in order to analyze the benefits of choosing Libera Brilliance.
Fermilab, Batavia
SLAC, Menlo Park, California
KEK, Ibaraki
A beam position monitor (BPM) upgrade at the KEK Accelerator Test Facility (ATF) damping ring is currently in progress, carried out by a KEK/FNAL/SLAC collaboration under the umbrella of the global ILC R&D effort. The upgrade consists of a high resolution, high reproducibility read-out system, based on analog and digital downconversion techniques, digital signal processing, also implementing a novel automatic gain error correction schema. The technical concept and realization, as well as preliminary results of the beam studies are presented.
I-Tech, Solkan
Libera Brilliance has proved successful in the field of beam diagnostics. High performance, system reliability and its high level of integration into accelerator control systems makes Libera a very accurate, robust and powerful measuring system. Although Libera Brilliance has been developed mainly for applications involving frequency domain processing, the flexibility makes it a good time domain measuring system for single pass applications. Moreover, there are other applications dealing with pulses, where a modified version of Libera Brilliance can be used. This is the case of beam phase and position measurements in accelerators, like Spiral2 (Ganil) and LANSCE (Los Alamos), dealing with heavy particles (protons, deuterons and heavy ions). The phase information extracted by the measurement in such systems is used to control the acceleration process of such heavy particles. This paper shows the approach adopted in processing the signals produced by such bunch trains. A modified Libera Brilliance unit, configured for the LANSCE bunch trains, has been tested by means of extensive laboratory measurements. Performance has been evaluated by applying different digital signal processing.
ORNL, Oak Ridge, Tennessee
The original wire-scanner software was written by one of the Spallation Neutron Source (SNS) partners, Los Alamos National Laboratory. This software was designed for the types of wire-scanners initially planned and their planned usage at that time. New variations in the wire-scanner hardware added gearing, different position read-back methods, and a timing card. The new software handles these additional hardware variations in a flexible manner through configuration files. The software upgrade allows the user to synchronize the stepping of the fork with external applications, such as loss monitors to study the losses caused by the wire. Another new functionality allows you to change what part of the beam pulse is used to determine the transverse profile after the data has been taken. This avoids having to do time consuming rescans if the timing was not perfectly setup. The new software, also a LabVIEW program, is structured around a state-machine with sequence capability to manage the complexities of stepping through a scan and interacting with the user. This paper discusses the features of the new software, the implementation, and the obtained results.
Bira, Albuquerque, New Mexico
National Instruments, Austin
LANL, Los Alamos, New Mexico
The design and test of a new beam-profile-wire-scanner actuator for the LANSCE* 800-MeV proton linear accelerator is described. Previous actuator implementations use open-loop stepper-motor control for position indexing. A fixed-frequency, fixed-duration pulse train is sent to the stepper motor driving the linear actuator. This has lead to significant uncertainties in position, mechanical resonances and electrical noise. A real-time, closed loop control system has been developed at tested for more repeatable and accurate positioning of beam sense wires. The use of real-time controller allows one to generate a velocity profile for precise, resonance-free wire position indexing. High radiation levels in the beam tunnel, dictate the use of an electro-magnetic resolver, typically, used in servo applications, as the position feedback element. Since the resolver is an inherently analog device sophisticated digital signal processing is required to generate and interpret the wave forms that the feedback mechanism needs for positioning. All of the electronic and computational duties are handled in one National Instruments compact RIO real-time chassis with FPGA.**
*Los Alamos Neutron Science Center
**Field Programmable Gate Array
LBNL, Berkeley, California
At the Advanced Light Source (ALS), imperfections in the injection system plus electron diffusion result in storage ring RF bucket contamination. A Virtex-4 FPGA is used to generate a Direct-Digital Synthesized (DDS) sinewave waveform at the vertical betatron tune frequency, which is synchronously gated on or off at the 1.6MHz ring orbit frequency. Any pattern on/off/invert in 328 buckets by 2ns at the ring orbit frequency can be set. An embedded Power-PC core in the FPGA provides TCP access for control and monitoring via a remote PC running LabVIEW.
CERN, Geneva
The unprecedented intensity and energy of the LHC proton beams will require an excellent control of the transverse beam dynamics in order to limit particle loss in the superconducting systems. Due to restricted tolerances of the machine protection system and tight beam emittance blow-up budget only small beam excitation is allowed, making precise measurements of the transverse beam parameters very challenging. This paper describes the systems measuring the tune, coupling and chromaticity of the LHC beams. As manual correction of these parameters may reach its limit with respect to required precision and expected time-scales, the LHC is the first proton collider that can be safely and reliably operated only with automatic feedback systems for controlling the transverse beam dynamics. An outline of these systems is also presented.
ANL, Argonne
The Advanced Photon Source (APS) injection booster is a 7-GeV electron synchrotron with a ramping time of 220 ms and a repetition rate of 2 Hz. A real-time tune measurement system is needed in order to monitor and possibly correct tune drift during the 220-ms energy ramp. Such a drift may occur during user beam operations, especially during top-up operations, and results in shot-to-shot charge fluctuations. We designed and developed a new FPGA-based system that pings the beam at variable intervals and measures booster tune. A prototype system has been built and tested, and it has achieved the specified time resolution of 2 ms and a tune resolution of better than 0.002. This report describes the design and main parameters, test results from our preliminary commissioning, and application of such a system in ramping correction.
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.