DESY, Hamburg
The former electron and proton preaccelerator PETRA at DESY is currently reconstructed and will be converted into the most brilliant storage-ring-based X-ray source worldwide called PETRAIII. The commissioning is scheduled for January 2009. It will operate at 6 GeV with 100 mA stored current and with a design emittance of 1 nm rad. Top-up operation is foreseen right from the beginning to reduce changes in heat-load and thermal drifts to a minimum,. Suitable beam diagnostic instrumentation and machine protection systems have to be established to guarantee the low emittance, a sub-micron beam stability as well as a save machine operation. To ensure a very high availability of the beam in top-up mode, the injector and preaccelerator diagnostic systems will be refurbished as well. A complete overview of the instrumentation and their latest developments to achieve these goals will be presented.
JLAB, Newport News, Virginia
CNU, Newport News, Virginia
Beamline components used for diagnostic elements often rely on thermal stabilization, continual physical maintenance (ie. tuning), and frequent beam-based calibrations to maintain specified performance. Direct-sequence spread spectrum (DSSS) pilot tones injected into a particular element and combined with the beam-derived signal can subsequently be separated and used to assess performance degradation. In addition, the DSSS tone can be used as a real-time calibration signal, without interference to the intended diagnostic signal. This paper demonstrates such a technique in the design of a Beam Current Monitor downconverter system, as an intended upgrade to the CEBAF Beam Loss Accounting system. A brief spread-spectrum primer is included, as well as a description of appropriate spreading codes and their generation.
SLAC, Menlo Park, California
The growth rates of the longitudinal higher-order impedance-driven modes beam have greatly increased since the initial PEP-II design and commissioning. This increase is attributed to the addition of 8 1.2 MW RF klystrons and 12 accelerating cavities, as well as to operations at twice the design current and almost four times the luminosity. As a result, the requirement for the longitudinal feedback has greatly increased since the design, and the feedback filters and control schemes have evolved during PEP-II operations. In this paper growth and damping rate data for the high-order cavity driven beam modes are presented and compared with historical estimates and measurements. The available margins for the 4 A LER and 2.2 HER ring case at PEP-II are estimated, and suggestions for reliable operation are also presented. The effect of noise in the feedback processing channel is also studied. Data for different gain configurations of the filter from PEP and other accelerators are presented. These data show the tradeoff between instability control and higher noise levels.
KEK, Ibaraki
SLAC, Menlo Park, California
Dimtel, San Jose
A bunch-by-bunch feedback system has been developed to suppress longitudinal coupled-bunch instabilities at the KEK-PF. A generalpurpose signal processor, called iGp, has been developed by a collaboration among KEK, SLAC and INFN-LNF. A longitudinal kicker based on the DAΦNE-type over-damped cavity was designed and installed in the ring. The whole feedback loop was closed at the end of June 2007. The longitudinal dipole-mode instabilities are successfully suppressed up to 430 mA. The performance and the details of the system will be presented in this paper.
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.
I-Tech, Solkan
ESRF, Grenoble
Libera, the beam position processor, features the so-called Turn-by-Turn (TbT) data output, the data rate being exactly the revolution frequency of the accelerator. This data is essential for commissioning of the accelerator as well as for various machine physics studies. However, due to the "natural" properties of correctly structured filters (respecting the Nyquist theorem), the smearing between adjacent TbT samples is not negligible. The purpose of the modified DDC filter is to remove smearing between adjacent TbT samples, especially with partial fill patterns. The usage of Modified DDC filters gives the best results for the studies using the Turn-by-Turn measurements, with the benefit of "true & pure" Turn-by-Turn results (no smearing). The method, its implementation and first results are discussed in this paper.
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.
KEK, Ibaraki
Button electrodes with good time response are essential for the bunch-by-bunch feedback / diagnostic systems needed for future short-bunch-spacing accelerators, such as energy recovery linacs (ERL) or a super B-factory. The impedance matching and time-domain response of electrodes, particularly around the vacuum seal, have been studied using 3-D electromagnetic codes (HFSS, MAFIA and GdfidL). Several candidates have been fabricated to examine the tolerance for mechanical pressures and heat stress due to the welding process. The real beam response from a short bunch has also been studied using a test-beam line at the KEK-PF injector beam transport section.
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
BNL, Upton, Long Island, New York
In this paper we present algorithm of coupling correction in a storage ring based on monitoring the vertical size of a stored beam, while varying skew quadrupoles. The details of the algorithm realized as Matlab script and experimental results of its application are presented.
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.
Fermilab, Batavia
Monitoring the tunes of individual proton and antiproton bunches is crucial to understanding and mitigating the beam-beam effects in the Tevatron collider. To obtain a snapshot of the evolving bunch-by-bunch tune distribution a simultaneous treatment of all the bunches is needed. The digital tune monitor (DTM) was designed to fulfill these requirements. It uses a standard BPM as a pickup. The vertical proton monitor is installed and allows us to gain valuable operational experience. A major upgrade is underway to implement an automatic bunch-by-bunch gain and offset adjustment to maintain the highest possible sensitivity under real operational conditions. We present the concept of the DTM along with its technical realization as well as the latest experimental results. Major challenges from the design and operation point of view are discussed.
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.