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feedback

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MOD1A01 Digital EBPMs at Diamond: Operational Experience and Integration into a Fast Global Orbit Feedback storage-ring, power-supply, pick-up, controls 24
 
  • G. Rehm, M. G. Abbott, J. Rowland, I. Uzun
    Diamond, Oxfordshire
  We present out experience with the Libera EBPM during the first months of operation at Diamond. Measurement noise and beam current dependence with beam are compared to earlier lab measurements. Where discrepancies between the performance in the lab and in the application are observed, the causes have been investigated. Furthermore, results of the integration of the EBPMs into a FOFB system are presented, including measurements of orbit motion spectra with and without FOFB.  
 
TUO1A02 Feedbacks on Tune and Chromaticity controls, coupling, resonance, synchrotron 43
 
  • R. J. Steinhagen
    CERN, Geneva
  Feedbacks on tune, coupling and chromaticity are becoming an integral part of safe and reliable accelerator operation. Tight tolerances on beam parameters typically constrain the allowed oscillation amplitudes to the micrometre range, leaving only a small margin for the transverse beam and momentum excitations required for tune and chromaticity measurements. This contribution presents an overview of these beam-based feedback systems, their architecture and design choices involved. It discusses performance limitations due to cross-constraints, non-linearities, the coupling between multiple nested loops, and the interdependence of beam parameters.  
slides icon Slides  
 
TUO1A03 Beam Diagnostic Features of the ESRF Multibunch Feedback kicker, diagnostics, pick-up, controls 48
 
  • J. M. Koch, F. Epaud, G. A. Naylor, E. Plouviez
    ESRF, Grenoble
  The ESRF storage ring is now equiped with a set of multibunch feedback systems. The main goal of the implementation of these systems is to prevent longitudinal and transverse instabilities. However, beside this main function, these systems provide a powerful diagnostic to study the longitudinal and transverse beam dynamic and document operation problems. In this paper we give a short overview of these feedback systems and describe their diagnostics function in more detail.  
 
TUPB02 Stripline Transversal Filter Techniques For Sub-Picosecond Bunch Timing Measurements diagnostics, synchrotron, controls, vacuum 54
 
  • J. D. Fox, T. Mastorides
    SLAC, Menlo Park, California
  Measurement of time of arrival of a particle bunch is a fundamental beam diagnostic. The PEP-II/ALS/BESSY/PLS longitudinal feedback systems use a planar stripline circuit structure to convert a 30 ps beam BPM impulse signal into a 4 cycle tone burst at the 6th harmonic of the accelerator RF frequency (roughly 3 GHz). A phase-detection technique is used to measure the arrival time of these BPM impulses with 180 fs rms single-shot resolution (out of a 330 ps dynamic range). Scaled in frequency, this approach is directly applicable to LCLS, FEL and other sub-fs regime pulse and timing measurements. The transversal circuit structure is applicable to measurement of microbunches or closely spaced bunches (the PEP-II examples make independent measurements at 2 nS bunch spacing) and opens up some new diagnostic and control possibilities. This paper reviews the principles of the technique, and uses data from PEP-II operations to predict the limits of performance of this measurement scheme for arrival phase measurement. These predictions are compared with results in the literature from electro-optic high-resolution sub-picosecond beam timing and phasing diagnostics.

* Briggs, et al, "Prompt Bunch by Bunch Synchrotron Oscillation Detection by a Fast Phase Measurement", Proceedings of the IEEE Particle Accelerator Conference, 5/91, 1404-1406

 
 
TUPB04 BPM detectors upgrade for the ELETTRA Fast Orbit Feedback electron, controls, closed-orbit, diagnostics 60
 
  • M. Lonza, L. Battistello, D. Bulfone, R. De Monte, S. Fontanini, V. Forchi', G. Gaio, F. Giacuzzo, R. Marizza, R. Passuello, L. Pivetta, C. Scafuri
    ELETTRA, Basovizza, Trieste
  The project of a fast feedback system to stabilize the closed orbit of the Elettra storage ring is in an advanced stage. All of the existing BPMs have been equipped with new digital detectors in order to provide precise and high-rate position measurements to the feedback system. A new beam position interlock system has also been installed to protect the vacuum chamber from synchrotron radiation produced by insertion devices. This paper presents features and performance of the new orbit measurement system and reports some preliminary results of the feedback commissioning.  
 
TUPB07 Electric -In-Air-X-Ray- Detectors for high Resolution Vertical Beam Position Measurement at the ESRF diagnostics, dipole, vacuum, emittance 69
 
  • K. B. Scheidt
    ESRF, Grenoble
  The tiny fraction of the very hard X-rays that fully penetrate the dipole absorber structure and enter the free air space behind it can be detected in different ways to yield precise information on the vertical characteristics of the electron beam. In addition to a system of imaging detectors to measure the emittance, a 2nd detector type was developed that yields a direct electric signal. It consists of a high-Z blade in conjuction with a small In-Air ionization slot that generates a direct strong electric signal allowing for nanometer resolution measurements of vertical beam motion in a spectrum upto 1KHz. The high resolution performance of this detector type is explained by the fact that it touches the heart and center of the beam whereas other devices (X-BPMs or e-BPMs) have to work on the edges or tails of the beam or feel the beam indirectly by wall-current pick-ups. The results obtained with prototypes will be presented together with the prospects of an installation of 8 units in 2007. The intrinsic advantages of this In-Air detector like costs and simplicity, thanks to a total absence of cooling and UHV requirements, will be emphasized.  
 
TUPC20 The SOLEIL BPM and Orbit Feedback Systems controls, storage-ring, vacuum, instrumentation 189
 
  • N. Hubert, L. Cassinari, J.-C. Denard, N. L. Leclercq, A. Nadji, L. S. Nadolski, D. Pédeau
    SOLEIL, Gif-sur-Yvette
  SOLEIL is a third generation light source built in France, near Paris. Its BPM system is important for machine studies and for delivering stable beams to the users. A beam stable to 1/10th of the dimensions requires submicron stability in the vertical plane. The monitors, anchored either to the girders or to the ground, are fixed points of the vacuum chamber. Bellows avoid transverse drifts due to mechanical stress. The electronics design was driven by combined efforts through an active communication between accelerator labs (SOLEIL at first, later joined by DIAMOND) and Instrumentation Technologies. The result is the “Libera Electron” beam position processor. It combines a 0.2μm rms resolution and micron level stability for beam delivery with accurate turn-by-turn measurements (3μm resolution at 0.8MHz) for machine commissioning and beam physics studies. It also features position interlock, tune measurement, and postmortem capabilities. A Slow Orbit Feedback for correcting low frequency drifts (0 to 0.1Hz) is currently in operation. The Fast Orbit Feedback to be implemented soon will suppress higher frequency perturbations up to 100Hz.  
 
WEPB02 Design of an Intra-Bunch-Train Feedback System for the European X-Ray FEL kicker, pick-up, dipole, electron 232
 
  • B. Keil, G. J. Behrmann, M. Dehler, R. Kramert, G. Marinkovic, P. Pollet, M. Roggli, M. Rohrer, T. Schilcher, V. Schlott, D. M. Treyer
    PSI, Villigen
  • J. Lund-Nielsen, D. Nölle, M. Siemens, S. Vilcins
    DESY, Hamburg
  After joining the preparatory phase of the European X-ray FEL project, the Paul Scherrer Institute agreed in taking over responsibility for electron beam stabilization by developing a fast intra-bunch-train feedback (IBFB) system, which will be tested in its prototype version at the FLASH linac of the collaboration partner DESY. The proposed IBFB topology consists of two beam position monitors ("upstream BPMs") followed by two kicker magnets for each transverse plane and two more BPMs ("downstream BPMs"). By measuring the position of each bunch at the upstream BPMs and applying suitable transverse kicks individually to the following bunches, the architecture of the FPGA-based digital IBFB electronics (with a latency preferably below the bunch spacing of 200 ns and 1000 ns for the XFEL and FLASH) allows to damp beam motions up to hundreds of kHz. In addition to the FPGA-based feedback, DSPs enable adaptive feed-forward correction of repetitive beam motions as well as feedback parameter optimisation using the downstream BPMs. This paper gives an overview of the architecture and status of the IBFB subsystems being developed, like stripline BPMs, digital electronics and kicker magnets.  
 
WEPB15 A Sub-50 Femtosecond bunch arrival time monitor system for FLASH laser, pick-up, electron, polarization 262
 
  • F. Löhl, K. E. Hacker, H. Schlarb
    DESY, Hamburg
  A bunch arrival time monitor system using the future laser based synchronization system at FLASH has been developed. The signal of a beam pick-up with several GHz bandwidth is sampled by a sub-ps laser pulse using a broadband electro-optical modulator. Bunch arrival time deviations are converted into amplitude modulations of the sampling laser pulses which are then detected by a photo-detector. A resolution of 30 fs could be reached, with the capability towards sub-10 fs level. In this paper we describe the design of the optical system and we present recent results.  
 
WEPB16 First prototype of an optical cross-correlation based fiber-link stabilization for the FLASH synchronization system laser, polarization, free-electron-laser, electron 265
 
  • F. Löhl, H. Schlarb
    DESY, Hamburg
  • J. Chen, F. X. Kaertner, J. Kim
    MIT, Cambridge, Massachusetts
  A drift free synchronization distribution system with femtosecond accuracy is of great interest for free-electron-lasers such as FLASH or the European XFEL. Stability at that level can be reached by distributing laser pulses from a mode-locked erbium-doped fiber laser master oscillator over actively optical-length stabilized fiber-links. In this paper we present a prototype of a fiber-link stabilization system based on balanced optical cross-correlation. The optical cross-correlation offers drift-free timing jitter detection. With this approach we were able to reduce the timing jitter added by a 400 m long fiber-link installed in a noisy accelerator environment to below 10 fs (rms) over 12 hours.  
 
WEPB21 Kicker Based Tune Measurement for DELTA kicker, betatron, storage-ring, resonance 277
 
  • P. Hartmann, J. Fürsch, T. Weis, K. Wille
    DELTA, Dortmund
  • R. Wagner
    Bergische Universität Wuppertal, Wuppertal
  We have set up a tune measurement for the electron storage ring Delta based on broadband beam excitation with a kicker magnet and measurement of the relaxation betatron oscillations turn-by-turn. By averaging over several kicks the kick amplitude may be as low as 600 nrad in standard user runs at nominal current, leading to negligible beam distortion. Signal to noise ratios in excess of 10 are reliably achieved down to 200 uA beam current using a maximum kicker amplitude of 10 urad. A simple tune feedback algorithm compensates for tune shifts due to vacuum chamber movement and orbit movement in sextupoles.  
 
WEPB28 First Tests of the Transverse Multibunch Feedback at Diamond pick-up, damping, kicker, instrumentation 295
 
  • A. F.D. Morgan, G. Rehm, I. Uzun
    Diamond, Oxfordshire
  This paper describes the design and initial tests of the transverse multibunch feedback system under development at Diamond. The system is designed to damp instabilities up to 250MHz in both the vertical and horizontal plane. This will lead to an increase of instability thresholds which will permit a reduction of chromaticity and thus should improve dynamic aperture and life time.  
 
WEPC01 Beam Based Measurements of RF Phase and Amplitude Stability at FLASH gun, laser, acceleration, electron 307
 
  • H. Schlarb, C. Gerth, W. Koprek, F. Löhl, E. Vogel
    DESY, Hamburg
  Beam based techniques to determine the phase and amplitude stability of the photo-cathode laser, the RF gun and superconducting acceleration modules become key tools for the understanding and quality control for FEL operation critical acceleration sub-system. The measurements are used to identify the sources of instabilities, to determine response functions and to optimize RF feedback parameters and algorithm. In this paper, an overview on the measurement techniques and their limitation is given, together with some important results on the currently achieved RF and laser stability.  
 
WEPC04 Transverse Feedback Development at SOLEIL impedance, damping, emittance, betatron 316
 
  • R. Nagaoka, L. Cassinari, J.-C. Denard, J.-M. Filhol, N. Hubert, M.-P. Level, P. Marchand, C. Mariette, F. Ribeiro, R. Sreedharan
    SOLEIL, Gif-sur-Yvette
  • K. Kobayashi, T. Nakamura
    JASRI/SPring-8, Hyogo-ken
  The SOLEIL ring is planned to operate in both multibunch and high current per bunch modes. However, the small vertical chamber aperture around the SOLEIL ring enhances the transverse impedance both in its resistive-wall and broadband content, resulting in instabilities that appear at relatively low current compared to the desired values. A decision was therefore taken to install a digital bunch-by-bunch feedback system, with an aim to make it operational from the beginning of the user operation. The system implemented comprises components developed elsewhere, particularly the FPGA processor of Spring-8, chosen among different possible solutions. Using a BPM and a stripline in the diagonal mode, a single unit of the FPGA processor board has shown to successfully suppress resistive-wall and ion induced instabilities in either one or both transverse planes up to 300 mA. The paper discusses the system characteristics including striplines whose shunt impedance was maximised by keeping the coupling impedance small*, the obtained performance as well as future extensions to overcome the encountered limitations.

* C. Mariette ID1209

 
 
WEPC10 Tune, Coupling, and Chromaticity Measurement and Feedback During RHIC Run 7 injection, coupling, betatron, controls 331
 
  • P. Cameron, J. Cupolo, W. C. Dawson, C. Degen, A. J. Della Penna, L. T. Hoff, Y. Luo, A. Marusic, R. Schroeder, C. Schultheiss, S. Tepikian
    BNL, Upton, Long Island, New York
  Tune feedback was first implemented in RHIC in 2002, as a specialist activity. The transition to full operational status was impeded by dynamic range problems, as well as by overall loop instabilities driven by large coupling. The dynamic range problem was solved by the CERN development of the Direct Diode Detection Analog Front End[1]. Continuous measurement of all projections of the betatron eigenmodes made possible the world's first implementation of coupling feedback during beam acceleration, resolving the problem of overall loop instabilites[2,3]. Simultaneous tune and coupling feedbacks were utilized as specialist activities for ramp development during the 2006 RHIC run. At the beginning of the 2007 RHIC run there remained two obstacles to making these feedbacks fully operational in RHIC - chromaticity measurement and control, and the presence of strong harmonics of the power line frequency in the betatron spectrum. Preliminary investigations of power line harmonics were presented earlier[4]. We report here on progress in tune, coupling, and chromaticity measurement and feedback, and discuss the relevance of our results to the LHC commissioning effort.

[1] M. Gasior and R. Jones, DIPAC 2005, Lyon, p.312.[2] P. Cameron et. al., PRST-AB, Dec 2006. [3] R. Jones et. al., DIPAC 2005, Lyon, p.298.[4] P. Cameron et. al., DIPAC 2005, Lyon, p.33.

 
 
WEPC16 Excitation Striplines for SOLEIL Fast Transverse Feedback impedance, simulation, vacuum, kicker 343
 
  • C. Mariette, J.-C. Denard, R. Nagaoka
    SOLEIL, Gif-sur-Yvette
  SOLEIL, the French third generation light source, is equipped with excitation striplines for a tune monitor and for the (bunch-by-bunch) Fast Transverse Feedback* that has been recently implemented. A careful design of the striplines and their vacuum feedthroughs was aimed at maximizing the effectiveness of the excitation power via high shunt impedances, and minimizing the power taken from the beam via low parasitic mode losses. Three stripline kickers have been developed for these applications. We report on their design using RADIA and GdfidL simulation codes, on the fabrication of the striplines, and on the experimental results with beam.

* R. Nagaoka: Transverse Feedback Development at SOLEIL. ID 1257

 
 
WEPC17 Fast Orbit Feeback System Upgrade with New Digital Bpm and Power Supply in the Tls power-supply, controls, electron, vacuum 346
 
  • C. H. Kuo, J. Chen, P. C. Chiu, K. T. Hsu, K. H. Hu, K.-B. Liu
    NSRRC, Hsinchu
  • A. Bardorfer
    Instrumentation Technologies, Solkan
  The BPMs of orbit feedback loop use analogy type in the TLS that is more than 10 years. The analogy type BPM provides high resolution position detection after signal processing. The new generation digital beam position monitor (DBPM) was performed recently. The BPM electronics are commercial available by using direct RF sampling technology, FPGA, and embedded control environment running GNU/Linux. The programmable nature of DBPM system is beneficial for multi-mode high precision beam diagnostics purposes. Sub-micron resolution is achieved for averaged beam position measurement with high update rate. The DBPM are seamless integrated with existed control system and is compatible with old BPM in the orbit feedback loop. In the same time, the corrector power-supply is also upgraded for wide bandwidth control. The integration of old and new BPM, power-supply control for fast orbit feedback will be discussed in this report.  
 
WEPC22 Synchronization of a 3GHz Repetition Rate Harmonically Mode-Locked Fiber Laser for Optical Timing Applications laser, polarization, controls, linac 358
 
  • L. Banchi, M. Ferianis, F. Rossi
    ELETTRA, Basovizza, Trieste
  • A. Bogoni, P. Ghelfi, L. Poti'
    CNIT, Pisa
  We have successfully stabilized a 3GHz Harmonically Mode-Locked fiber ring laser by a PLL feedback control of the cavity length to reduce the pulses RMS timing jitter. The laser cavity is composed of all PM fibers and components to eliminate polarization instabilities and to reduce the vibration sensitivity. The laser stability in terms of timing jitter was around 9ps in the range 10Hz-10MHz. Using a PLL scheme we synchronized the laser repetition rate to an ultra stable RF generator. The noise characteristics of the laser output were measured by observing the SSB noise spectra of the 1st harmonic, from 10Hz to the Nyquist frequency (1.5GHz). We have obtained a global reduction of fiber laser timing jitter value down to less than 100fs in the range 10Hz-10MHz; a complete overlapping between the laser and the RF generator spectral profiles in the loop bandwidth has been observed. An extended investigation has been performed to estimate the phase noise spectra and timing jitter up to 1.5GHz. By doing so, the contribution of the laser supermodes to the phase noise has been taken into account as well, to quantify the true value of the total RMS timing jitter of the optical pulses.  
 
WEPC26 Transverse Bunch-by-Bunch Feedback for the VEPP-4M Electron-Positron Collider kicker, betatron, coupling, impedance 367
 
  • V. P. Cherepanov, E. N. Dementyev, E. B. Levichev, A. S. Medvedko, V. V. Smaluk, D. P. Sukhanov
    BINP SB RAS, Novosibirsk
  Transverse mode coupling instability (TMCI or fast head-tail) is the principal beam current limitation of the VEPP-4M electron-positron collider. For the high-energy physics experiments at the 5.5 GeV energy, the VEPP-4M bunch current should exceed much the TMCI threshold. To suppress transverse beam instabilities, a broadband bunch-by-bunch digital feedback system is developed. The feedback concept is described, the system layout and first beam measurements are presented.  
 
WEO3A01 Low-Latency High-Resolution Single-Shot Beam Position Monitors pick-up, dipole, linac, alignment 376
 
  • D. M. Treyer
    PSI, Villigen
  In this paper design aspects of high-resolution, single-shot transverse beam position monitors (BPMs) are discussed. The focus is put on BPMs which can provide (sub-)micrometer precision at measurement speeds of less than a few hundred nanoseconds. Different pickups, analog signal conditioning electronics, and digital post processing schemes are reviewed. Their characteristics and limitations with respect to application in high-resolution, fast BPMs are pointed out. Exemplary implementations of successful BPM realizations found in the literature are reviewed. A specific implementation of a BPM based on a resonant stripline pickup, developed for a fast transverse feedback system for the European X-FEL, is also presented.