06 Instrumentation, Controls, Feedback & Operational Aspects

T05 Beam Feedback Systems

Paper Title Page
TUZM02 Overview of Fast Beam Position Feedback Systems 1021
 
  • D. Bulfone
    ELETTRA, Basovizza, Trieste
  
  Modern circular and linear accelerators often rely on fast beam position feedbacks for the achievement of their design parameters. Such systems have gone through a significant evolution, which has taken advantage of recent progress of the associated equipment, like beam position monitors, as well as of the hardware and software processing technologies. A review of the latest developments and foreseen designs at different accelerators is given.  
slides icon Slides  
WEOCG01 Orbit Feedback Trickery at the NSLS VUV Ring 1931
 
  • B. Podobedov
    BNL, Upton, Long Island, New York
  
  A couple of NSLS user groups has recently requested an unusual modification to the way the VUV ring orbit is controlled and stabilized. Rather than keeping the orbit as stable as possible they require a large (many transverse beam sizes) periodic orbit oscillation at the source points of their beamlines. During regular machine operations this has to co-exist with stable orbit throughout the rest of the ring. Achieving good orbit stability under these constraints presents an interesting control problem. Making use of control theory tools and Matlab / Simulink modeling we have explored various algorithms to allow for these new requirements. We then extended our digital orbit feedback system to incorporate these algorithms. In this paper we present commissioning results as well as comparison to the simulations.  
slides icon Slides  
THPC065 Orbit Stability Status and Improvement at SOLEIL 3134
 
  • L. S. Nadolski, J. C. Besson, F. Bouvet, P. Brunelle, L. Cassinari, J.-C. Denard, J.-M. Filhol, N. Hubert, J.-F. Lamarre, A. Loulergue, A. Nadji, D. Pedeau, M.-A. Tordeux
    SOLEIL, Gif-sur-Yvette
  
  SOLEIL is a 2.75 GeV third generation synchrotron light source delivering photons to beam-lines since January 2007. Stability of the beam-line source points is crucial for the user experiments. Typically this stability has to be below one tenth of the transverse beam sizes. This is challenging especially in the vertical plane leading to sub-micrometer values. This paper will describe the position stability achieved today without and with the slow orbit feedback. Impact of different noise sources and present limitations will be described. To end an improvement strategy will be given for short and medium terms.  
THPC113 Feedback Damper System for Quadrupole Oscillations after Transition at RHIC 3242
 
  • N. P. Abreu, M. Blaskiewicz, J. M. Brennan, C. Schultheiss
    BNL, Upton, Long Island, New York
  
  The heavy ion beam at RHIC undergoes a strong quadrupole oscillations just after it crosses transition, which in turn leads to an increase in bunch length making rebucketing less effective. A feedback system was built to damp these quadrupole oscillations and in this paper the characteristics of the system and the results obtained are presented and discussed.  
THPC114 Design and Performance of a Prototype Digital Feedback System for the International Linear Collider Interaction Point 3245
 
  • P. Burrows, B. Constance, H. Dabiri Khah, J. Resta-López
    JAI, Oxford
  • R. Apsimon, P. Burrows, C. I. Clarke, A. F. Hartin, C. Perry, C. Swinson
    OXFORDphysics, Oxford, Oxon
  • G. B. Christian
    ATOMKI, Debrecen
  • A. Kalinin
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  
  We present the design and preliminary results of a prototype beam-based digital feedback system for the Interaction Point of the International Linear Collider. A custom analogue front-end processor, FPGA-based digital signal processing board, and kicker drive amplifier have been designed, built, and tested on the extraction line of the KEK Accelerator Test Facility (ATF). The system was measured to have a base latency of approximately 140 ns, increasing to approximately 148 ns with the inclusion of real-time charge normalisation.  
THPC115 Commissioning of SOLEIL Fast Orbit Feedback system 3248
 
  • N. Hubert, L. Cassinari, J.-C. Denard, J.-M. Filhol, N. Leclercq, A. Nadji, L. S. Nadolski, D. Pedeau
    SOLEIL, Gif-sur-Yvette
  
  The Fast Orbit Feedback system at SOLEIL is fully integrated into the BPM system equipped with Libera modules. Indeed, the correction algorithm has been embedded into the Libera FPGA which directly drives the power supplies of dedicated air coil correctors. The beam position measurements of the 120 BPMs are distributed around the storage ring by a dedicated network. Then, the correction is computed and applied at a rate of 10 kHz to 48 correctors installed over stainless-steel bellows, on each side of every straight section. 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.  
THPC116 Commissioning of the iGp Feedback System at DAΦNE 3251
 
  • A. Drago
    INFN/LNF, Frascati (Roma)
  • J. D. Fox
    SLAC, Menlo Park, California
  • D. Teytelman
    Dimtel, San Jose
  • M. Tobiyama
    KEK, Ibaraki
  
  The iGp (Integrated Gigasample Processor) is an innovative digital bunch-by-bunch feedback system developed by a KEK/SLAC/INFN-LNF joint collaboration. The processing unit can sample at 500 MHz and compute the bunch-by-bunch output signal for up to 5000 bunches. The feedback firmware code is implemented inside just one FPGA (Field Programmable Gate Array) chip, a Xilinx Virtex-II. The FPGA implements two 16 taps FIR (Finite Impulse Response) filter that are realtime programmable through the operator interface. At DAΦNE, the Frascati PHI-Factory, two iGp units have been commissioned in the April 2007. The iGp systems have plugged in the previous betatron feedback systems. This insertion has been very fast and has shown no problems involving just a substitution of the old, less flexible, digital unit, letting unchanged the baseband analog frontend and the analog backend. The commissioning has been very simple, due to the complete and powerful EPICS operator interface, working well in local and remote operations. The software includes also tools for analyzing post processor data. A description of the commissioning with the operations done to find the best feedback setup are reported.  
THPC117 Measurements and Analysis of Beam Transfer Functions in the Fermilab Recycler Ring Using the Transverse Digital Damper System 3254
 
  • N. Eddy, J. L. Crisp, M. Hu
    Fermilab, Batavia, Illinois
  
  The Fermilab Recycler Ring Transverse Digital Damper System was designed to facilitate Beam Transfer Function measurements using a Network Analyzer connected to auxiliary system ports for timing and diagnostic purposes. The Digital Damper System has the capability for both open and closed loop measurements. The Beam Transfer Function measurements provide direct measurements of the machine impedance, beam stability, and beam parameters such as betatron tune and chromaticity. An overview of the technique is presented along with analysis and results from open and closed loop measurements in the Fermilab Recycler Ring.  
THPC118 Performance and Future Developments of the Diamond Fast Orbit Feedback System 3257
 
  • M. T. Heron, M. G. Abbott, J. A. Dobbing, G. Rehm, J. Rowland, I. Uzun
    Diamond, Oxfordshire
  • S. Duncan
    University of Oxford, Oxford
  
  The electron beam in the Diamond Synchrotron Light Source is stabilised in two planes using a Global Beam Orbit Feedback system. This feedback system takes the beam position from 168 Libera electron beam position monitors, for both planes, and calculates offsets to 336 corrector power supplies at a rate ~10kHz. The design and implementation will be summarised, and system performance and first operational experience presented. Current and potential future developments of the system will be considered.  
THPC119 Progress of TLS Fast Orbit Feedback System and Orbit Stability Studies 3260
 
  • C. H. Kuo, J. Chen, P. C. Chiu, K. T. Hsu, K. H. Hu, D. Lee
    NSRRC, Hsinchu
  
  The orbit feedback system of the TLS has been deployed for a decade and continuously upgraded. However, due to limitation of the existing hardware, the system cannot remove orbit excursion caused by the perturbation due to fast operation of insertion devices. The newly proposed orbit feedback system with the upgraded digital BPM system and switching corrector power supply system is planned to be installed and commissioned in late 2008. The preliminary calculation on the stability performance for the orbit feedback system is presented in the report. New fast orbit feedback system can be expected to achieve a submicron stability of the electron beam working at a bandwidth of at least 60 Hz.  
THPC120 Conceptual Design and Performance Estimation of The TPS Fast Orbit Feedback System 3263
 
  • P. C. Chiu, J. Chen, K. T. Hsu, K. H. Hu, C. H. Kuo
    NSRRC, Hsinchu
  
  A 3 GeV Synchrotron (TPS) is proposed in Taiwan. Its storage ring consists of 24 double-bend cells with 6-fold symmetry and the circumference is 518.4m. The report presents the initial design of the fast orbit feedback system (FOFB) for TPS. The system uses 168 BPMs and 168 correct magnets to stabilize global closed orbit at 10 kHz updated rate. The different subsystems are modeled: the BPM systems, the corrector magnet, vacuum chamber, and etc. The latency of the communication and computation is also studied. The preliminary calculation on the stability performance for the orbit feedback system is presented in the report. The FOFB is expected to achieve a submicron stability of the electron beam working at a bandwidth of at least 100 Hz.  
THPC121 LHC Transverse Feedback System and its Hardware Commissioning 3266
 
  • W. Höfle, P. Baudrenghien, F. Killing, Y. A. Kojevnikov, G. Kotzian, R. Louwerse, E. Montesinos, V. Rossi, M. Schokker, E. Thepenier, D. Valuch
    CERN, Geneva
  • E. V. Gorbachev, N. I. Lebedev, A. A. Makarov, S. Rubtsun, V. Zhabitsky
    JINR, Dubna, Moscow Region
  
  A powerful transverse feedback system ('damper') has been installed in LHC. It will stabilise coupled bunch instabilities in a frequency range from 3 kHz to 20 MHz and at the same time damp injection oscillations originating from steering errors and injection kicker ripple. The transverse damper can also be used as an exciter for purposes of abort gap cleaning or tune measurement. The power and low-level systems layout are described along with results from the hardware commissioning. The achieved performance is compared with earlier predictions and requirements for injection damping and instability control. Requirements and first measurements of the performance of the low-level system are summarized. The chosen approach for the low-level system using advanced FPGA technology is very flexible allowing implementation of future upgrades of the signal processing without changing the hardware.  
THPC122 Digital Signal Processing for the Multi-bunch LHC Transverse Feedback System 3269
 
  • W. Höfle, P. Baudrenghien, G. Kotzian, V. Rossi
    CERN, Geneva
  
  For the LHC a VME card has been developed that contains all functionalities for transverse damping, diagnostics and controlled bunch by bunch excitation. It receives the normalized bunch by bunch position from two pick-ups via Gigabit Serial Links (SERDES). A Stratix II FPGA is responsible for resynchronising the two data streams to the bunch-synchronous clock domain (40.08 MHz) and then applying all the digital signal processing: In addition to the classic functionalities (gain balance, rejection of closed orbit, pick-up combinations, one-turn delay) it contains 3-turn Hilbert filters for phase adjustment with a single pick-up scheme, a phase equalizer to correct for the non-linear phase response of the power amplifier and an interpolator to double the processing frequency followed by a low-pass filter to precisely control the bandwidth. Using two clock domains in the FPGA the phase of the feedback loop can be adjusted with a resolution of 10 ps. Built-in diagnostic memory (observation and post-mortem) and excitation memory for setting-up are also included. The card receives functions to continuously adjust its parameters as required during injection, ramping and physics.  
THPC124 The Manufacturing and Tests of The New Vertical Feedback Stripline at Soleil 3275
 
  • C. Mariette, J.-C. Denard, R. Nagaoka
    SOLEIL, Gif-sur-Yvette
  
  This paper describes the development of the kicker striplines for the bunch-by-bunch transverse instability feedback system at Soleil. A careful design of the striplines and of their vacuum feedthroughs was aimed at maximizing the effectiveness of the excitation power and minimizing the power taken from the beam. The excitation effectiveness improves with the shunt impedance. But, simultaneously, the beam impedance should be made as small as possible. We also found useful to estimate the temperature of the feedthroughs at high beam currents, especially on the ceramic-to-metal seals. We also report on the difficulties encountered with obtaining good feedthroughs.  
THPC125 Modeling and Simulation of the Longitudinal Beam Dynamics-RF Station Interaction in the LHC Rings 3278
 
  • T. Mastorides, J. D. Fox, C. H. Rivetta, D. Van Winkle
    SLAC, Menlo Park, California
  • P. Baudrenghien, J. Tuckmantel
    CERN, Geneva
  
  A non-linear time-domain simulation has been developed to study the interaction between longitudinal beam dynamics and RF stations in the LHC rings. The motivation for this tool is to study the effect of RF station noise, impedance, and perturbations on the beam life and longitudinal emittance. It will be also used to determine optimal LLRF configurations, to study system sensitivity on various parameters, and to define the operational and technology limits. It allows the study of alternative LLRF implementations and control algorithms. The insight and experience gained from our PEP-II simulation is important for this work. In this paper we discuss properties of the simulation tool that will be helpful in analyzing the LHC RF system and its initial results. Partial verification of the model with data taken during the LHC RF station commissioning is presented.  
THPC126 Performance and Features of the Diamond TMBF System 3281
 
  • A. F.D. Morgan, G. Rehm, I. Uzun
    Diamond, Oxfordshire
  
  The Diamond Transverse Multibunch Feedback System (TMBF) comprises an in-house designed and built analogue frontend to select and condition the position signals for each bunch. This is combined with the Libera Bunch-by-Bunch system to digitise the signal and perform the relevant calculations before driving the output stripline kickers. As the electronics are based on an FPGA this has allowed us to implement several features in addition to the basic feedback calculations. We report on improvements to both the analogue and digital parts of the TMBF system, along with recent achievements in using the system for instability mode stabilisation and for tune measurement. Also we discuss the potential of the system and additional functionality we plan on introducing in the near future.  
THPC127 Filling of High Current Singlet and Train of Low Bunch Current in SPring-8 Storage Ring 3284
 
  • T. Nakamura, T. Fujita, K. Fukami, K. Kobayashi, C. Mitsuda, M. Oishi, S. Sasaki, M. Shoji, K. Soutome, M. Takao, Y. Taniuchi
    JASRI/SPring-8, Hyogo-ken
  • T. Ohshima
    RIKEN/SPring-8, Hyogo
  • Z. R. Zhou
    USTC/NSRL, Hefei, Anhui
  
  We performed the storage of high current singlet of 10mA/bunch and a train of bunches of 0.3mA/bunch under the bunch by bunch feedback systems with newly developed bunch current sensitive automatic attenuators with FPGA. The automatic attenuator reduces the signal level of the high current bunch by factor three to five to avoid the saturation of the feedback systems. With this system, the feedback systems suppress horizontal and vertical mode-coupling instabilities and raise the bunch current limit from 3.5mA/bunch to 12mA/bunch, and simultaneously the systems suppress the multi-bunch instabilities by resistive-wall and cavity higher order mode impedances. The improvement of the automatic attenuation system to fit to the final target of the bunch current in the train, 0.06mA/bunch, are being performed. The other problems which limit the filling patterns, such as saturation of the readout electronics of the beam position monitor system and the heating of vacuum components by high current bunches, will be briefly presented.  
THPC128 Bunch by Bunch Feedback by RF Direct Sampling 3287
 
  • T. Nakamura, K. Kobayashi
    JASRI/SPring-8, Hyogo-ken
  • Z. R. Zhou
    USTC/NSRL, Hefei, Anhui
  
  Recent ADCs have wide analog band-width which is enough for direct sampling of the RF signal from a beam position monitor without down conversion. We employed such ADCs for our bunch-by-bunch signal processor* and performed the feedback with the direct RF sampling of the signal from a beam position monitor to detect the position of bunches. With RF direct sampling, the down conversion stage which is used in usual RF front-end circuits and is composed of mixers, filters, delays and base-band amplifiers is not necessary. This simplifies the systems, and reduces the costs and the number of the tuning parameters. The feedback system with RF direct sampling is now in operation at user mode in SPring-8.

*T. Nakamura, K. Kobayashi. "FPGA BASED BUNCH-BY-BUNCH FEEDBACK SIGNAL PROCESSOR", Proc. of ICALEPCS 05.

 
THPC130 Integrated Global Orbit Feedback with Slow and Fast Correctors 3292
 
  • I. Pinayev
    BNL, Upton, New York
  
  The NSLS-II Light Source which is planned to be built at Brookhaven National Laboratory will provide users with ultra-bright synchrotron radiation sources and is designed for horizontal beam emittances <1 nm. Full utilization of the very small emittances and beam sizes requires sub-micron orbit stability in the storage ring. This can be provided by means of a wide bandwidth orbit feedback system. Traditional approach is to utilize a uniform set of fast correctors or use two separate systems with strong slow and weaker fast correctors. In the latter case two systems need to communicate to suppress transients associated with different update rates of corrector settings. In this paper we consider an integrated system with two types of correctors. Its main feature is that setpoints of slow correctors are updated with the same rate as fast correctors; however the bandwidth is limited in order to stay in linear regime. Possible architectures and technical solutions as well as achievable performance are discussed.  
THPC131 On the Optimal Number of Eigenvectors for Orbit Correction 3295
 
  • I. Pinayev, M. G. Fedurin
    BNL, Upton, New York
  
  The singular value decomposition method is widely used for orbit correction in the storage rings. It is a powerful tool for inverting of the usually rectangular response matrices, which usually have rectangular form. Another advantage is flexibility to choose number of eigenvectors for calculation of required strengths of orbit correctors. In particular, by reduction in number of eigenvectors one can average over ensemble noise in the beam position monitors. A theoretical approach as well as experimental results on the NSLS VUV ring are presented.  
THPC132 Bunch by bunch Transverse Feedback Development at ESRF 3297
 
  • E. Plouviez, P. Arnoux, F. Epaud, J. M. Koch, G. A. Naylor, F. Uberto
    ESRF, Grenoble
  
  This paper describes the bunch by bunch transverse feedback implemented at ESRF. The first motivation of this project was to be able to cope with the constraint of the future operation of the ESRF with a stored current increased from 200mA to 300mA with a uniform or quasi uniform filling, but we were also interested in possible improvement of the operation with others filling patterns (16 and 4 bunches patterns for instance). Our system uses a classical scheme: The signal coming from a set of button type electrodes is demodulated in a homodyne RF front end and processed in a FPGA DSP to derive a correction signal which is applied to the beam with a wide band stripline kicker. Depending on the filling pattern of the storage ring (uniform filling or filling with a small number of high charge bunches), different kind of transverse instabilities have been observed in the past, due to the resistive wall impedance, ion trapping or mode coupling. We have tested the effect of our system in these different situation and report also the results of these tests.  
THPC133 Layout and Simulations of the FONT System at ATF2 3300
 
  • J. Resta-López, P. Burrows
    JAI, Oxford
  
  We describe the adaptation of a Feedback On Nano-second Timescales (FONT) system for the final focus test beam line ATF2 at KEK. This system is located in the ATF2 extraction line, and is mainly conceived for cancellation of transverse jitter positions originated in the damping ring and by the extraction kickers. This jitter correction is performed by means of a combination of feed-forward (FF) and fast-feedback (FB) beam stabilisation. We define optimal positions for the kicker and BPM pairs of the FONT FF/FB system, and estimate the required kicker performance and BPM resolutions. Moreover simulation results are presented.  
THPC136 Design and Commissioning of a Bunch by Bunch Feedback System for the Australian Synchrotron 3306
 
  • M. J. Spencer, G. LeBlanc, K. Zingre
    ASP, Clayton, Victoria
  
  A transverse bunch feedback system has been designed in order to fight the effects of coupled bunch instabilities. This system is currently in the commissioning phase. A digital system was chosen because of its flexibility and diagnostic potential. While the major components were sourced from a private company, time has also been spent on in house development of an analogue front-end and the diagnostic components of the software.  
THPC139 Properties of X-ray Beam Position Monitors at the Swiss Light Source 3312
 
  • T. Wehrli, M. Böge, J. Krempasky, E. D. van Garderen
    PSI, Villigen
  
  Tungsten blade type X-ray beam position monitors (X-BPMs) are widely used at the SLS to stabilize the photon beam position at the the micron level. Various slow (~0.5 Hz) photon beam position feedbacks (SPBPFs) being an integral part of the global orbit feedback system have been in operation for several years. They are solely based on one X-BPM reading assuming that the photon beam movement is dominated by angle changes of the electron beam. This paper reports on the operation of the first SPBPF using two X-BPMs. This allows the separation of positional and angular variations of the electron beam, which is of special importance for the recently commissioned PolLux dipole beamline, as it is mostly sensitive to position changes. Correlations between the electron beam movement and the X-BPM readings are extensively analyzed in order to disentangle systematic errors of the position determination and real orbit motion. Methods are presented on how to recognize and correct or even avoid large systematic errors of the X-BPMs. With this knowledge, the demanding requirements on X-BPM accuracy in case of a SPBPF utilizing two X-BPMs could be fulfilled for the first time at the SLS.  
THPC140 The Performance of a Fast Closed Orbit Feedback System with Combined Fast and Slow Correctors 3315
 
  • L.-H. Yu, S. Krinsky, O. Singh, F. J. Willeke
    BNL, Upton, Long Island, New York
  
  For NSLSII closed orbit feedback system, in order to reduce the noise caused by the step changes of the power supplies in the feedback system, the angular kick corresponding to the last bit of the power supplies for the fast correctors must be smaller than 3 nrad*. On the other hand, in order to carry out closed orbit alignment or orbit correction after a long term drift, we need strong correctors with 0.8 mrad kick strength*. In order to avoid the requirement of correctors with both large strength and very small minimum step size, we consider separate sets of slow correctors with large strength and fast correctors with smaller maximum strength. In order to avoid fast and slow feedback systems working in parallel, and avoid the possible interaction between two feedback systems, we consider the possibility of using only one fast feedback system with slow correctors periodically removing the DC components of the fast correctors so that the DC components in fast feedback system would not accumulate to reach saturation even after a large long term drift of the closed orbit motion. We report on simulation of the performance of this combined system for NSLSII in this paper.

* NSLSII Preliminary Design Report (2007)

 
THPP114 LHC Transverse Feedback Damping Efficiency 3632
 
  • G. Kotzian, W. Höfle
    CERN, Geneva
  • E. Vogel
    DESY, Hamburg
  
  A simulation model has been developed to predict the damping efficiency of the LHC transverse feedback system in the presence of coupled bunch instabilities and under realistic assumptions for the injection error. The model tracks both the centre of gravity of a bunch and the r.m.s beam size during and after injection. It includes the frequency characteristic of the transverse feedback system. Nonlinearities in the beam optics will cause the bunches to filament and lead to an increase of the transverse emittance after injection. The resistive wall instability reduces the effectiveness of the transverse feedback by slowing down the damping process. Possibilities for enhancing the performance of the feedback system by signal processing schemes are outlined.