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damping

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MOPC120 J-PARC RCS Non-linear Frequency Sweep Analysis resonance, controls, impedance, acceleration 346
 
  • A. Schnase, K. Haga, K. Hasegawa, M. Nomura, F. Tamura, M. Yamamoto
    JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
  • S. Anami, E. Ezura, K. Hara, C. Ohmori, A. Takagi, M. Toda, M. Yoshii
    KEK, Ibaraki
  A standard method to measure the S21-transfer function of a system of amplifier and cavity involves a network analyzer and a linear or logarithmic frequency sweep. However, to characterize the transfer function of the broadband (Q=2) RCS RF system, we measure and analyze several harmonics at the same time under high power ramping conditions. A pattern driven DDS system generates frequency and amplitude as in accelerator operation. During the 20ms acceleration part of the cycle, a large memory oscilloscope captures the RF-signals. The data are analyzed off-line with a down-conversion process like in a multi-harmonic LLRF-system, resulting in multi-harmonic amplitude and phase information. Using this setup in the cavity test phase we were able to find and cure resonances before installation into the tunnel. We show examples. RCS is in the commissioning phase and has reached the milestone of acceleration to final energy and beam extraction. 10 RF systems are in operation, and the low-level RF system controls the fundamental h(2) and the second harmonic h(4). Using a multi-harmonic analysis during beam operation allows checking the RF system behavior with and without beam-loading.  
 
MOPP009 Copper Prototype Measurements of the HOM, LOM and SOM Couplers for the ILC Crab Cavity dipole, simulation, polarization, coupling 568
 
  • G. Burt, P. K. Ambattu, A. C. Dexter
    Cockcroft Institute, Lancaster University, Lancaster
  • L. Bellantoni
    Fermilab, Batavia, Illinois
  • P. Goudket, P. A. McIntosh
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • Z. Li, L. Xiao
    SLAC, Menlo Park, California
  The ILC Crab Cavity is positioned close to the IP and hence is very sensitive to the wakefields induced by the beam. A set of couplers were designed to couple to and hence damp the spurious modes of the crab cavity. As the crab cavity is a deflecting mode cavity, it operates using a dipole mode and has different damping requirements than an accelerating mode cavity. A separate coupler is required for the monopole modes below the operating frequency of 3.9 GHz, known as the LOMs, the opposite polarization of the operating mode, the SOM, and the modes above the operating frequency, the HOMs. Each of these couplers have been manufactured out of copper and measured attached to an aluminium nine cell prototype of the cavity and their external Q factors were measured. The results were found to agree well with numerical simulations.  
 
MOPP017 A Kicker Driver Exploiting Drift Step Recovery Diodes for the International Linear Collider kicker, instrumentation, linear-collider, collider 589
 
  • F. O. Arntz, M. P.J. Gaudreau, A. Kardo-Sysoev, M. K. Kempkes, A. Krasnykh
    Diversified Technologies, Inc., Bedford, Massachusetts
  Diversified Technologies, Inc. (DTI) is developing a driver for a kicker strip-line deflector which inserts and extracts charge bunches to and from the electron and positron damping rings of the International Linear Collider. The kicker driver must drive a 50 Ω terminated TEM deflector blade at 10 kV with 2 ns flat-topped pulses, which according to the ILC pulsing protocol, bursts pulses at a 3 MHz rate within one-millisecond bursts occurring at a 5 Hz rate. The driver must also effectively absorb high-order mode signals emerging from the deflector. In this paper, DTI will describe current progress utilizing a combination of high voltage DSRDs (Drift Step Recovery Diodes) and high voltage MOSFETs. The MOSFET array switch, without the DSRDs, is itself suitable for many accelerator systems with 10 – 100 ns kicker requirements. DTI has designed and demonstrated the key elements of a solid state kicker driver which both meets the ILC requirements, is suitable for a wide range of kicker driver applications. Full scale development and test are exptected to occur in Phase II of this DOE SBIR effort, with a full scale demonstration scheduled in 2009.  
 
MOPP025 Design of the Beam Extraction by Using Strip-line Kicker at KEK-ATF kicker, septum, extraction, injection 601
 
  • T. Naito, H. Hayano, K. Kubo, S. Kuroda, T. Okugi, N. Terunuma, J. Urakawa
    KEK, Ibaraki
  The developing work of the strip-line kicker system for International linear collider(ILC) is carrying out at KEK*. To confirm the performance of the kicker system, the beam extraction test by using strip-line kicker is in progress at KEK-ATF. The multi-bunch beam, which has 2.8ns bunch spacing in the damping ring, is extracted from the damping ring to the extraction line with 308ns duration. The scheme is the same as the kicker of the ILC. The bump orbit and the auxiliary septum magnet will be used with the kicker to clear the geometrical restriction. The detail of the hardware design and the basic performance of each component are presented in this paper.

*T. Naito et al. Development of the Strip-line Kicker System for ILC Damping Ring, Proceedings of PAC07, Albuquerque, New Mexico, USA, pp2772-2274.

 
 
MOPP047 Simulation Studies on the Vertical Emittance Growth at the Existing ATF Extraction Beamline emittance, extraction, multipole, coupling 652
 
  • F. Zhou, J. W. Amann, S. Seletskiy, A. Seryi, C. M. Spencer, M. Woodley
    SLAC, Menlo Park, California
  Significant dependence of the vertical emittance growth on the beam intensity was experimentally observed at the Accelerator Test Facility (ATF) at KEK extraction beamline. This technical note describes the simulations of possible vertical emittance growth sources, particularly in the extraction channel, where the magnets are shared by both the ATF extraction beamline and its damping ring. The vertical emittance growth is observed in the simulations by changing the beam orbit in the extraction channel, even with all optics corrections. The possible reasons for the experimentally observed dependence of the vertical emittance growth on the beam intensity are discussed. An experiment to measure the emittance versus beam orbit at the existing ATF extraction beamline is underway*.

*M. Alabau et al. Study of Abnormal Vertical Emittance Growth in ATF Extraction Line, this proceeding.

 
 
MOPP049 Collective Effects in the CLIC Damping Rings impedance, space-charge, ion, emittance 658
 
  • G. Rumolo, J. B. Jeanneret, Y. Papaphilippou, D. Quatraro
    CERN, Geneva
  The possible performance limitations coming from collective effects in the CLIC damping rings are the subject of this paper. In particular, the consequences of space charge, due to the very high beam brilliance, and of the resistive wall impedance, due to the locally very small beam pipe, are considered potentially dangerous in spite of the high beam energy. Hence, they have been studied in detail with the HEADTAIL code, which has been modified in order to take into account a finer lattice structure as well as multi-bunch effects of the resistive wall wake field. The study aims at setting the intensity thresholds determined by these phenomena.  
 
MOPP050 Electron Cloud Build Up and Instability in the CLIC Damping Rings electron, wiggler, simulation, positron 661
 
  • G. Rumolo, Y. Papaphilippou
    CERN, Geneva
  • W. Bruns
    WBFB, Berlin
  Electron cloud can be formed in the CLIC positron damping ring and cause intolerable tune shift and beam instability. 2D and 3D build up simulations with the Faktor2 code, developed at CERN, have been done to predict the cloud formation in the arcs and wigglers of the damping rings. HEADTAIL simulations have been used to study the effect of this electron cloud on the beam and assess the thresholds above which the electron cloud instability would set in.  
 
MOPP051 Effect of Fill Patterns on Extraction Jitter in Damping Rings simulation, extraction, injection, coupling 664
 
  • K. M. Hock, A. Wolski
    Cockcroft Institute, Warrington, Cheshire
  Injection of fresh bunches into a storage ring can induce jitter on stored bunches, as a result of wake field coupling. This transient effect can lead to an undesirable increase in the emittance of stored bunches; in the case of linear collider damping rings, there can also be jitter in the extracted bunches, which can adversely affect performance. We consider how the wake field coupling in a storage ring depends on the fill pattern, and, for the ILC damping rings, present the results of simulations of the transverse dynamics with a resistive wall wake field for a number of different fill patterns. We draw correlations between the extraction jitter and various machine parameters, including the fill pattern.  
 
MOPP055 A Comparison of Tuning Strategies for a Linear Collider Damping Ring emittance, lattice, quadrupole, closed-orbit 667
 
  • J. K. Jones
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
  Emittance preservation is an important aspect in the design and running of any new Linear Collider design, with a direct consequence on the luminosity of the machine. Damping rings provide the lower limit on achievable emittance, and so are designed to produce as small a vertical emittance as possible, not only for luminosity considerations, but also to relax tolerances in downstream, emittance diluting, systems. Maintaining such small emittances requires that the damping ring emittance is regularly “tuned”. Several methods of damping ring tuning are investigated, and analysed both in terms of their relative effectiveness, under a variety of conditions, and the non-monetary cost involved in implementing and using the various algorithms.  
 
MOPP056 Beam Coupling Impedance in the ILC Damping Rings impedance, insertion, vacuum, coupling 670
 
  • M. Korostelev, O. B. Malyshev, A. Wolski
    Cockcroft Institute, Warrington, Cheshire
  • A. F. Grant, J. Lucas
    STFC/DL, Daresbury, Warrington, Cheshire
  The ILC damping rings have stringent specifications for beam quality and stability. To avoid instabilities, the various components in the vacuum chamber will need to be carefully designed to minimize the longitudinal and transverse wake fields. We present the results of impedance calculations for various components that are expected to make a significant contribution to the overall machine impedance.  
 
MOPP059 Study for ILC Damping Ring at KEKB emittance, electron, optics, sextupole 676
 
  • K. Ohmi, J. W. Flanagan, H. Fukuma, K.-I. Kanazawa, H. Koiso, M. Masuzawa, Y. Ohnishi, K. Oide, Y. Suetsugu, M. Tobiyama
    KEK, Ibaraki
  • M. T.F. Pivi
    SLAC, Menlo Park, California
  ILC damping ring consists of very low emittance electron and positron storage rings. It is necessary for ILC damping ring to study electron cloud effects in such low emittance positron ring. We propose a low emittance operation of KEKB to study the effects.  
 
MOPP060 Parameter Scan for the CLIC Damping Rings emittance, wiggler, coupling, target 679
 
  • Y. Papaphilippou, H.-H. Braun, M. Korostelev
    CERN, Geneva
  Triggered by the RF frequency reduction of the CLIC main linac cavities, the damping ring parameters had to be reevaluated and the rings' performance adapted to the new luminosity requirements. In view of a staged approach for reaching the ultimate energy of the collider, the dependence of the rings output emittances under the influence of Intrabeam Scattering is evaluated with respect to different beam characteristics such as bunch population, beam energy, coupling and longitudinal beam characteristics.  
 
MOPP061 Non Linear Dynamics Study of the CLIC Damping Rings Using Sympletic Integrators sextupole, wiggler, resonance, emittance 682
 
  • Y. Papaphilippou
    CERN, Geneva
  • Ch. Skokos
    IMCCE, Paris
  A class of symplectic integrators with positive steps (SABA2) is applied to investigate the non-linear dynamics of the CLIC damping rings. The detrimental effect of the chromaticity sextupoles is studied using frequency and diffusion maps and verified with MADX ptc dynamic aperture tracking. The reduction of the dynamic aperture for off-momentum particles is also investigated.  
 
MOPP062 Optics Design Considerations for the CLIC Pre-damping Rings emittance, focusing, quadrupole, optics 685
 
  • Y. Papaphilippou
    CERN, Geneva
  • F. Antoniou
    National Technical University of Athens, Zografou
  The CLIC pre-damping rings have to accommodate a large emittance beam, coming in particular from the positron source and reduce its size to low enough values for injection into the main damping rings. Linear lattice design options based on an analytical approach for theoretical minimum emittance cells are presented. In particular the parameterisation of the quadrupole strengths and optics functions with respect to the emittance and drift lengths is derived. Complementary considerations regarding constraints imposed by positron stacking and input momentum spread are also considered.  
 
MOPP066 Recent Experimental Study of Fast Ion Instability in ATF Damping Ring ion, emittance, vacuum, single-bunch 697
 
  • N. Terunuma, Y. Honda, T. Naito, J. Urakawa
    KEK, Ibaraki
  • Eckhard. Elsen, G. X. Xia
    DESY, Hamburg
  The Fast Ion Instability (FII) is one of the very high priorities of the damping ring R&D for the International Linear Collider (ILC). The Accelerator Test Facility (ATF) in KEK can provide an ILC damping ring-like beam. A specific FII study in ATF has been launched to characterize this phenomenon for the ILC damping ring. A new gas inlet system has been installed recently in the ATF damping ring to control the ion effect. After N2 gas injection into the vacuum chamber in south straight section of the ring, FII has been observed for elevated gas pressures. Beam size blow-up and emittance growth for various fill patterns are presented in this paper and attributed to FII. Comparison between experimental data and simulation results are given as well.  
 
MOPP067 Coupling Correction Simulations for the ILC Damping Rings emittance, simulation, quadrupole, lattice 700
 
  • K. G. Panagiotidis, A. Wolski
    Cockcroft Institute, Warrington, Cheshire
  The ILC damping rings are specified to operate with a vertical emittance of 2 pm. To achieve this challenging goal, an effective diagnostic and correction system will be needed; however, BPMs add impedance to the ring, and diagnostics and correctors add complexity and cost. It is therefore desirable to understand how the final achievable emittance depends on the numbers, locations, and performance of the BPMs and correctors, and to determine the minimum number of these components required. We present the results of simulations for the damping rings, indicating the effectiveness of coupling correction for different design scenarios of the diagnostics and correction systems.  
 
MOPP068 Simulation Study of Fast Ion Instability in the ILC Damping Ring feedback, ion, simulation, electron 703
 
  • G. X. Xia, Eckhard. Elsen
    DESY, Hamburg
  The so-called fast ion instability potentially constitutes a performance limitation for the damping ring of the International Linear Collider (ILC). Based on the latest baseline lattice of the ILC damping ring the fast ion instability is simulated using a weak-strong code. Various fill patterns are examined to mitigate the onset of the instability. Feedback mechanisms are explored. The growth time of the fast ion instability is estimated for various vacuum pressures on the basis of the simulated results.  
 
MOPP081 Engineering Design of a PETS Tank Prototype for CTF3 Test Beam Line vacuum, beam-losses, alignment, controls 739
 
  • D. Carrillo, L. García-Tabarés, J. L. Gutierrez, I. Rodriguez, E. Rodríguez García, S. Sanz, F. Toral
    CIEMAT, Madrid
  • G. Arnau-Izquierdo, N. C. Chritin, S. Doebert, G. Riddone, I. Syratchev, M. Taborelli
    CERN, Geneva
  • J. Calero
    CEDEX, Madrid
  In the CLIC concept, PETS (Power Extraction and Transfer Structure) role is to decelerate the drive beam and transfer RF power to the main beam. One of the CTF3 test beam line (TBL) aims is to study the decelerated beam stability and evaluate PETS performance. The PETS core is made of eight 800 mm long copper rods, with very tight tolerances for shape (± 20 micron), roughness (less than 0.4 micron) and alignment (± 0.1 mm). Indeed, they are the most challenging components of the tank. This paper reports about the methods of fabrication and control quality of these bars. A special test bench has been designed and manufactured to check the rod geometry by measuring the RF fields with an electric probe. Other parts of the PETS tank are the power extractor, the waveguides and the vacuum tank itself. Industry is partially involved in the prototype development, as the series production consists of 15 additional units, and some concepts could be even applicable to series production of CLIC modules  
 
MOPP083 Status of High Power Tests of Normal Conducting Single-cell Structures impedance, klystron, vacuum, electron 742
 
  • V. A. Dolgashev, S. G. Tantawi
    SLAC, Menlo Park, California
  • Y. Higashi, T. Higo
    KEK, Ibaraki
  We report results of ongoing high power tests of single cell traveling wave and standing wave structures. These tests are part of an experimental and theoretical study of rf breakdown in normal conducting structures at 11.4 GHz*. The goal of this study is to determine the gradient potential of normal-conducting, rf powered particle beam accelerators. The test setup consists of reusable mode launchers and short test structures and powered by SLAC’s XL-4 klystron. The mode launchers and structures were manufactured at SLAC and KEK and tested in SLAC klystron test laboratory.

*V. A. Dolgashev, S. G. Tantawi, et al. “High Power Tests of Normal Conducting Single Cell Structures,” SLAC-PUB-12956, PAC07, Albuquerque, New Mexico, 25-29 June 2007, pp 2430-2432.

 
 
MOPP094 Reduction of Q-loss-effects in Ferrite-loaded Cavities synchrotron, resonance, vacuum 772
 
  • H. G. Koenig, S. Schaefer
    GSI, Darmstadt
  Accelerating cavities loaded with Ni-Zn ferrites have been widely used in synchrotrons for many years. So far their performance is significantly limited by the so-called high-loss-effect (HLE) or quality-loss-effect (QLE). After some milliseconds, this effect leads to a sudden drop of the resonator's voltage namely under the following conditions: fixed frequencies with RF-power above a specific threshold level and a parallel DC-biasing. The mechanism of this unwanted loss has not been fully understood yet. Now a simple method has been found to work against this effect with the aid of mechanical damping of surface waves. For small samples of ferrites the QLE is fully suppressed by using a rubber belt around the circumference or by covering the surface with a thin layer of hot-melt adhesive. We were able to show that similar methods applied to full size rings lead to a significant increase of the onset voltage of the QLE. Most of the existing ferrite loaded accelerating cavities with QLE-limitations can be increased in their accelerating voltage by the above-mentioned modification.  
 
MOPP108 Status of HOM Damped Room-temperature Cavities for the ESRF Storage Ring coupling, impedance, simulation, storage-ring 808
 
  • V. Serriere, A. K. Bandyopadhyay, L. Goirand, J. Jacob, D. Jalas, B. Ogier, A. Triantafyllou
    ESRF, Grenoble
  • N. Guillotin
    SOLEIL, Gif-sur-Yvette
  At the ESRF, longitudinal coupled bunch instabilities driven by cavity HOM are currently avoided up to the nominal current of 200 mA by precisely controlling the temperatures of the six five-cell cavities installed on the storage ring. A longitudinal bunch by bunch feedback has recently allowed to overcome the remaining HOM and thereby increase the current in the storage ring to 300 mA. In parallel, HOM damped room-temperature cavities are being developed for highly reliable passive operation at 300 mA. They are designed for a possible later upgrade to higher currents.  
 
MOPP112 Status of the PEFP Superconducting RF Project superconducting-RF, linac, proton, controls 820
 
  • S. An, Y.-S. Cho, B. H. Choi, C. Gao, Y. M. Li, Y. Z. Tang, L. Zhang
    KAERI, Daejon
  Superconducting RF project of the Proton Engineering Frontier Project (PEFP) aims to develop a superconducting RF linac to accelerate a proton beam above 80 MeV at 700 MHz. The preliminary design of a low-beta cryomodule has been completed. A low-beta (β=0.42) cavity, a higher-mode coupler and a fundamental power coupler (FPC) for the PEFP cavities have also been designed. A FPC baking system and high power RF conditioning system are under construction. A helium vesel made of stainless steel has been designed. A new tuner has also been designed. Two prototype copper cavities have been produced and tested. The HOM coupler has been measured on the copper cavities. A cryostat for a SRF cavity vertical testing has been designed.  
 
MOPP127 Commissioning of Superconducting Linac at IUAC - Initial Challenges and Solutions linac, acceleration, vacuum, scattering 856
 
  • S. Ghosh, S. Babu, J. Chacko, A. Choudhury, G. K. Chowdhury, T. S. Datta, D. Kanjilal, S. Kar, M. Kumar, A. Mandal, D. S. Mathuria, R. S. Meena, R. Mehta, K. K. Mistri, A. Pandey, P. Patra, P. N. Prakash, A. Rai, A. Roy, B. K. Sahu, S. S. Sonti, J. Zacharias
    IUAC, New Delhi
  During initial acceleration of ion beam through the first module of linac having eight superconducting (SC) niobium quarter wave resonators (QWR), energy gains were found to be much lower. Major problem encountered was limitation of accelerating fields in the QWR achieved at much higher RF power (up to 300 W) leading to cable melting, metal coating on SC surface and increased cryogenic losses. Cold leaks in the niobium-stainless steel transition assemblies and niobium tuner bellows also posed a major challenge. A novel way of damping mechanical vibration was implemented to reduce RF power. Cooling was improved by installing a hemispherical structure on the resonator. The drive coupler was redesigned to eliminate metal coating. Design of the tuner/transition flange assemblies was modified to avoid cold leak. After incorporation of these modifications, on-line beam acceleration through Linac was accomplished. Pulsed (1.3 ns) Silicon beam of 130 MeV from Pelletron accelerator was further bunched to 250 ps by SC Superbuncher. After acceleration through the linac module and subsequent re-bunching using SC Rebuncher, 158 MeV Silicon beam having pulse width of 400 ps was delivered.  
 
MOPP140 Status and Test Results of High Current 5-cell SRF Cavities Developed at JLAB dipole, impedance, simulation, quadrupole 886
 
  • F. Marhauser, G. Cheng, G. Ciovati, W. A. Clemens, E. Daly, D. Forehand, J. Henry, P. Kneisel, S. Manning, R. Manus, R. A. Rimmer, C. Tennant, H. Wang
    Jefferson Lab, Newport News, Virginia
  A new compact CW cryomodule development for use in future ERLs and FELs is underway at JLAB. Five-cell SRF cavities have been built at 1497 MHz for moderate RF input power scenarios with waveguide endgroups to efficiently transfer the beam induced HOM energy to room temperature loads. Effort has been made as well to provide a good real-estate gradient, cryogenic efficiency and HOMs tuned to safe frequencies to minimize HOM power extracted from the beam. Preliminary tests carried out earlier for two single-cell cavities at 1497 MHz cavity -one with a waveguide endgroup- and a bare 1497 MHz five-cell cavity have exceeded gradient and Qo specifications with no signs of multipacting and encouraged us to built two fully equipped 1497 MHz five-cell cavities. We report on the latest test results and the HOM impedance budget of the cavity used to evaluate BBU limits based on special machine optics.  
 
MOPP152 Bunch Lengthening Harmonic System for NSLS-II ion, impedance, injection, emittance 904
 
  • J. Rose, N. A. Towne
    BNL, Upton, Long Island, New York
  NSLS-II is a new ultra-bright 3GeV 3rd generation synchrotron radiation light source. The performance goals require operation with a beam current of 500mA and a bunch current of at least 0.5mA. Ion clearing gaps are required to suppress ion effects on the beam. The natural bunch length of 3mm is planned to be lengthened by means of a third harmonic cavity in order to provide a margin for the Touschek limited lifetime and for instability threshold currents. The paper presents the analysis of the bunch lengthening in this dual RF system consisting of a 500MHz fundamental and 1500 MHz harmonic system in presence of strong transient beam loading. A conceptual design of a 1500MHz SCRF cavity is developed and design performance is discussed.  
 
MOPP155 Superconducting RF Deflecting Cavity Design and Prototype for Short X-ray Pulse Generation simulation, coupling, collider, dipole 913
 
  • J. Shi, H. Chen, C.-X. Tang
    TUB, Beijing
  • G. Cheng, G. Ciovati, P. Kneisel, R. A. Rimmer, G. Slack, L. Turlington, H. Wang
    Jefferson Lab, Newport News, Virginia
  • D. Li
    LBNL, Berkeley, California
  • A. Nassiri, G. J. Waldschmidt
    ANL, Argonne, Illinois
  Deflecting RF cavities are proposed to be used in generating short x-ray pulses (on ~1-picosecond order) at the Advanced Photon Source (APS) at Argonne National Laboratory (ANL)* using a novel scheme by Zholents**. To meet the required deflecting voltage, impedance budget from higher order, lower order and the same order modes (HOM, LOM and SOM) of the APS storage ring, extensive deflecting cavity design studies have been conducted with numerical simulations and cavity prototypes. In this paper, we report recent progress on a single cell S-band (2.8-GHz) superconducting deflecting cavity design with waveguide damping. A copper and a niobium prototype cavity were fabricated and tested, respectively to benchmark the cavity and damping designs. A new damping scheme has been proposed which provides stronger damping to both HOM and LOM by directly coupling to a damping waveguide on the cavity equator.

* A. Nassiri, private communication, 2007
** A. Zholents et al. NIM, 1999, A425:385-389.

 
 
TUXM01 Ultra Low Emittance Light Sources emittance, optics, lattice, controls 988
 
  • J. Bengtsson
    BNL, Upton, New York
  The talk will cover the special issues for reaching sub-nm emittance in a storage ring. Effects of damping wigglers, intra-beam scattering and life-time issues, instabilities, dynamic aperature optimisation, control of optics, dispersion and orbit correction. Results and example of upgrades to existing machine and NSLS-II and Petra-III should be given.

First priority

 
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TUOCM02 X-ray Monitor Based on Coded-aperture Imaging for KEKB Upgrade and ILC Damping Ring photon, optics, synchrotron, monitoring 1029
 
  • J. W. Flanagan, H. Fukuma, S. Hiramatsu, H. Ikeda, K.-I. Kanazawa, T. Mitsuhashi, J. Urakawa
    KEK, Ibaraki
  • J. P. Alexander
    CLASSE, Ithaca
  • M. A. Palmer
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • G. S. Varner
    UH, Honolulu, HI
  We present here design considerations for an x-ray monitor for high-resolution (a few um) and fast response (sub-nanosecond) for beam profile measurements to be used at an upgraded KEKB and/or ILC damping ring. The optics for the monitor are based on a technique borrowed from x-ray astronomy, coded-aperture imaging, which should permit broad-spectrum, low-distortion measurements to maximize the observable photon flux per bunch. Coupled with a high-speed digitizer system, the goal is to make sub-bunch-length, turn-by-turn measurements of beam profile and position.  
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TUPC089 Robust Emittance Evaluation from Complex Transverse Phase Spaces emittance, background, electron, booster 1263
 
  • A. R. Rossi, A. Bacci
    INFN-Milano, Milano
  We present a novel procedure to analyze the transverse phase space of low energy electron bunches, close to a beam waist, in order to retrieve a sound estimate of its emittance. The procedure consist in a genetic code and a non linear fit applied in cascade, the first feeding the parameters starting values of the former. This allows us to cleanse the phase space from noise, separate the core charge from the halos and distinguish between bunch components undergoing different dynamics, such as cross over or the double emittance minima effect. Our procedure performs a rough longitudinal beam tomography, based on dynamical considerations, using transverse data. The application of the procedure to some experimental data is shown.  
 
TUPP033 Alternative Scheme of Bunch Length Compression in Linacs for Free Electron Lasers linac, simulation, bunching, laser 1610
 
  • S. Di Mitri, M. Cornacchia, S. V. Milton, S. Spampinati
    ELETTRA, Basovizza, Trieste
  The aim of this paper is to investigate the effect of an alternative scheme of bunch compression on the development of the microbunching instability. Two cases have been considered, one in the presence of a linear energy chirp at the compressor end and another without it. It is shown that after removing the linear energy chirp, a properly tuned R56 transport matrix element is able to dilute the initial energy modulation without affecting the bunch length and to damp the associated current spikes. A by-product of this study indicates that the global compression scheme can be further optimized in the direction of a double compression scheme in which the longitudinal Landau damping is enhanced by increasing the compression factor of the first compressor while reducing that of the second one. The limiting case of such a configuration is the single compression scheme at low energy. The study is based on analytical calculations and on the simulation code LiTrack.  
 
TUPP037 Impedance and Instabilities for the ALBA Storage Ring impedance, synchrotron, vacuum, storage-ring 1622
 
  • T. F. Günzel, F. Pérez
    ALBA, Bellaterra
  The geometrical impedance in all 3 planes for most of the vacuum chamber elements of the ALBA storage ring was computed with the 3D-solver GdfidL. Optimisation of some element geometries was carried out in order to reduce dissipative losses and in general the impedance. Resistive wall impedance was calculated analytically. The thresholds of various instabilities were determined on the basis of analytically formulated threshold criteria. The most important are a HOM-driven longitudinal multibunch instability and the transverse resistive wall instability. It is proposed to combat the first one by Landau damping using partial filling and the second one by a transverse feedback system.  
 
TUPP059 Study of Controlled Longitudinal Emittance Blow-up for High Intensity LHC Beams in the CERN SPS emittance, synchrotron, quadrupole, beam-loading 1676
 
  • G. Papotti, T. Bohl, T. P.R. Linnecar, E. N. Shaposhnikova, J. Tuckmantel
    CERN, Geneva
  Preventive longitudinal emittance blow-up, in addition to a fourth harmonic Landau damping RF system, is required to keep the LHC beam in the SPS stable up to extraction. The beam is blown-up in a controlled way during the acceleration ramp by using band-limited phase noise targeted to act inside the synchrotron frequency spread, which is itself modified both by the second RF system and by intensity effects (beam loading and others). For a high intensity beam these latter effects can lead to a non-uniform emittance blow-up and even loss of stability for certain bunches in the batch. In this paper we present studies of the emittance blow-up achieved with high intensity beams under different conditions of both RF and noise parameters.  
 
TUPP061 Comparison between Laboratory Measurements, Simulations and Analytical Predictions of the Resistive Wall Transverse Beam Impedance at Low Frequencies impedance, simulation, coupling, luminosity 1679
 
  • F. Roncarolo
    UMAN, Manchester
  • F. Caspers, T. Kroyer, E. Métral
    CERN, Geneva
  • B. Salvant
    EPFL, Lausanne
  The prediction of the resistive wall transverse beam impedance at the first unstable betatron line (8 kHz) of the CERN Large Hadron Collider (LHC) is of paramount importance for understanding and controlling the related coupled-bunch instability. Until now only novel analytical formulas were available at this frequency. Recently, laboratory measurements and numerical simulations were performed to crosscheck the analytical predictions. The experimental results based on the measurement of the variation of a probe coil inductance in the presence of i) sample graphite plates, ii) stand-alone LHC collimator jaws and iii) a full LHC collimator assembly are presented in detail. The measurement results are compared to both analytical theories and simulations. In addition, the consequences for the understanding of the LHC impedance are discussed.  
 
TUPP082 Longitudinal Stability of Flat Bunches with Space-charge or Inductive Impedance impedance, synchrotron, space-charge, dipole 1721
 
  • F. Zimmermann
    CERN, Geneva
  • I. Santiago Gonzalez
    University of the Basque Country, Bilbao
  We study the loss of Landau damping for the longitudinal plane via the ''Sacherer formalism''. Stability limits are calculated for several longitudinal beam distributions, in particular for two types of flat bunches, which could be of interest to the LHC upgrade. The resulting Landau stability diagrams are computed and displayed for different azimuthal modes. A general recipe is given for calculating the threshold intensity in the case of a capacitive impedance below transition or, equivalently, for a purely inductive impedance above transition. Specific results are finally presented for the case of the PS Booster, as an example of space-charge impedance below transition, and for the SPS, as an example of inductive impedance above transition.  
 
TUPP098 The 3D Space Charge Field Solver MOEVE and the 2D Bassetti-Erskine Formula in the Context of Beam - E-cloud Interaction Simulations positron, simulation, space-charge, electron 1759
 
  • A. Markovik, G. Pöplau, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
  In this paper the fields computed with our 3D space charge field solver MOEVE are compared to those obtained by means of the Bassetti-Erskine formula, which is a widely used 2D approximation of the electric field of a Gaussian bunch. In particular we are interested in the transversal fields of very flat bunches as the ILC or the KEKB positron bunch. Supposing a longitudinal Gaussian distribution of the bunches, we compare the computed transversal fields for a certain line density of the positron bunch. It turns out that the fields from the 2D and the 3D computation coincide very good.  
 
TUPP109 Meshless Solution of the Vlasov Equation Using a Low-discrepancy Sequence site, synchrotron, simulation, controls 1776
 
  • R. L. Warnock
    SLAC, Menlo Park, California
  • J. A. Ellison, K. A. Heinemann, G. Q. Zhang
    UNM, Albuquerque, New Mexico
  A successful method for solving the nonlinear Vlasov equation is the semi-Lagrangian method, in which the phase space density is represented by its values on a fixed Cartesian grid with interpolation to off-grid points. Integration for a time step consists of following orbits backward in time from initial conditions on the grid, with the collective force frozen during the time step. We ask whether it would be more efficient to use scattered data sites rather than grid points, namely sites from a low-discrepancy sequence as used in quasi - Monte Carlo integration. This requires a technique for interpolation of scattered data, and with such a technique in hand one can try either backward or forward orbits. Here we explore the forward choice, with the data sites themselves following forward orbits. We treat a problem well studied by the backward method, longitudinal motion in the SLAC damping rings. Over one or two synchrotron periods results are encouraging, in that the number of data sites can be reduced by a large factor. Over longer times it appears that the sites must be redistributed or changed in number from time to time, because of clustering.  
 
TUPP160 Superconducting RF Activities at ACCEL Instruments storage-ring, controls, cryogenics, superconducting-RF 1884
 
  • M. Pekeler, S. Bauer, P. vom Stein
    ACCEL, Bergisch Gladbach
  We report on highlights of SRF activities at ACCEL Instruments during the last few years. For example the development of a new hydrofloric and sulphoric acid free electropolishing method for niobium cavities and the construction and installation of a new standard electropolishing plant for 9-cell 1.3 GHz cavities. In addition we have further developed our design for 500 MHz superconducting RF modules for light sources and delivered three such accelerator modules for Shanghai Ligth Source. For SOLEIL we manufactured a 350 MHz twin cavity accelerator module using the technology of sputtering niobium onto copper.  
 
WEOBG01 CLIC RF High Power Production Testing Program recirculation, target, beam-losses, linac 1909
 
  • I. Syratchev, G. Riddone
    CERN, Geneva
  • S. G. Tantawi
    SLAC, Menlo Park, California
  The CLIC Power Extraction and Transfer Structure (PETS) is a passive microwave device in which bunches of the drive beam interact with the impedance of the periodically loaded waveguide and generate RF power for the main linac accelerating structure. The demands on the high power production (~ 150 MW) and the needs to transport the 100 A drive beam for about 1 km without losses make the PETS design rather unique and the operation very challenging. In coming years the intensive PETS testing program will be implemented. The target is to demonstrate full performance of the PETS operation. The testing program overview and test results available to date will be presented.  
slides icon Slides  
 
WEPC001 Status of PETRA III wiggler, vacuum, alignment, quadrupole 1977
 
  • K. Balewski
    DESY, Hamburg
  PETRA III is a new hard x-ray synchrotron radiation source which will be operated at 6 GeV with a extremely low horizontal emittance of 1nmrad. This new light source will be the result of a conversion of the existing accelerator PETRA II into a light source. The conversion comprises the complete rebuilding of one eighth of the 2304 m long storage ring, which will then house 14 undulator beam lines and the modernisation and refurbishment of the remaining seven eighths. In addition two 100m long damping wiggler section will be installed which are required to achieve the small design emittance. During the last four years extensive design work, construction and production of components have been carried out to prepare for the conversion. Since the 2nd of July the construction activities have started when PETRA II was no longer needed as a pre-accelerator for HERA. At present the project is still on track so that operation with beam is foreseen for January 2009 and first user experiments in the second half of 2009. In this report a brief overview of the project and the status of the constructional work, the different components and the installation in the tunnel will be given.  
 
WEPC029 Assessment of the Impact of External Stimuli on the Floor Stability of Diamond survey, storage-ring, site, monitoring 2049
 
  • J. Kay, H. C. Huang
    Diamond, Oxfordshire
  • R. Bartolini
    JAI, Oxford
  Continuous vibration monitoring is carried out and the stability of the Diamond floor slab has been assessed with regard to how it has responded to various external stimuli. Data has been collected on weather conditions and comparison made at extremes with floor vibration. The impact of a high level walkway bridge on the hall floor has also been assessed and there was a unique opportunity for an operational facility to measure the vibration response during a complete power black-out. The impact of local construction work is also presented.  
 
WEPC112 The Acceptance and Photon Beam Formation in SLS FEMTO Beamline laser, radiation, background, electron 2264
 
  • L. M. Hovhannisyan, D. K. Kalantaryan, V. M. Tsakanov
    CANDLE, Yerevan
  • S. T. Hakobyan
    YSU, Yerevan
  • A. Streun
    PSI, Villigen
  The FEMTO insertion at the Swiss Light Source (SLS) produces sub-ps X-ray pulses by modulating the electron energy in a slice of the bunch through interaction with a fs-laser. The radiation from the sliced bunch in the FEMTO undulator of the SLS storage ring has been studied. Only photons passing all apertures of the beam line arrive at the experiment. We derive the transverse phase space distribution of these photons, the radiation spectra, and the spatial and angular distribution. Transmission of the radiated photons through the FEMTO beamline is calculated using the SRW simulation code in order to evaluate the acceptance of the beamline and the photon beam phase space distribution at the experimental station.  
 
WEPC132 Damping Wigglers at the PETRA III Light Source wiggler, permanent-magnet, emittance, storage-ring 2317
 
  • M. Tischer, K. Balewski
    DESY, Hamburg
  • A. M. Batrakov, I. V. Ilyin, D. Shichkov, A. V. Utkin, P. V. Vagin, P. Vobly
    BINP SB RAS, Novosibirsk
  We report on the progress in construction of the PETRA III damping sections. A series of 10 permanent magnet wigglers followed by SR-absorbers will be installed in each of the two damping sections. Thereby, the emittance of the 6 GeV storage ring will be reduced down to 1 nmrad. Prototypes of all major components have meanwhile been characterized and a test assembly of one complete wiggler cell has been performed successfully. The wigglers have a period length of 200 mm and provide a peak field of 1.5 T. Most of the 4 m long devices have been fabricated and assembled. We present results of magnetic measurements and tuning.  
 
WEPD003 Manufacture and Test of a Small Ceramic-insulated Nb3Sn Split Solenoid collider, vacuum, linear-collider, undulator 2404
 
  • B. Bordini, R. Maccaferri, L. Rossi, D. Tommasini
    CERN, Geneva
  A small split solenoid wound with high Jc Nb3Sn conductor, constituted by a 0.8 mm Rod Re-stack Process (RRP) strand, was built and tested at CERN in order to study the applicability of:
  1. ceramic wet glass braid insulation without epoxy impregnation of the magnet;
  2. a new heat treatment devised at CERN and particularly suitable for reacting RRP Nb3Sn strands.
This paper briefly describes the solenoid and the experimental results obtained during 4.4 K and 1.9 K tests. The split solenoid consists of two coils (25 mm inner diameter, 51.1 mm outer diameter, 12.9 mm height). The coils were initially separately tested, in an iron mirror configuration, and then tested together in split solenoid configuration. In all the tests at 4.4 K the coils reached a current higher than 97% of their short sample limits at the first quench; in split solenoid configuration the maximum field in the coils and in the aperture were respectively 10.7 T and 12.5 T. At 1.9 K the coils had premature quenches due to self field instability despite the rather high RRR of the two coils (190 and 270). This phenomenon at 1.9 K, expected by our theory* and also confirmed by strand measurements, is discussed.

*B. Bordini, E. Barzi, S. Feher, L. Rossi, and A. V. Zlobin. "Self-Field Effects in Magneto-Thermal Instabilities for Nb-Sn Strands," to be published in IEEE Trans. Appl. Supercond. 2008.

 
 
WEPP007 Crab Compensation for LHC Beams impedance, optics, collimation, luminosity 2536
 
  • R. Calaga
    BNL, Upton, Long Island, New York
  • Y. Sun, R. Tomas, F. Zimmermann
    CERN, Geneva
  An R&D program to establish a road map for the installation of crab cavities in the LHC is rapidly advancing. Both local and global crab schemes are under investigation to develop cavities that will be compatible with LHC optics and meet aperture requirements. The design of a prototype TM110 cavity and pertinent RF requirements including impedance estimates and damping are discussed. Some alternate cavity designs are also explored. The required optics modifications to accommodate the crab cavities and some particle stability studies are presented.  
 
WEPP081 Wake-fields and Beam Dynamics Simulations for ILC ACD Accelerating Cavities emittance, linac, simulation, higher-order-mode 2707
 
  • C. J. Glasman, R. M. Jones
    UMAN, Manchester
  The ILC aims at colliding bunches of electrons and positrons at a centre of mass energy of 0.5 TeV and in a proposed upgrade to 1 TeV. These bunches of charged particle are accelerated in superconducting linacs. The baseline design for the ILC relies on the relatively mature TESLA-style cavities, with a proposed gradient of more than 30 MV/m and is known as the baseline configuration document (BCD). However, here we investigate electromagnetic fields in superconducting cavities, with the potential to reach accelerating gradients in excess of 50 MV/m, and these are the subject of the alternative configuration document (ACD). We analyse the band structure and necessary damping requirement of the wake-fields in two design configurations: Cornell's re-entrant cavity and KEK's Ichiro cavity. The emittance dilution arising from beams subjected to injection offsets and from cavity misalignments are studied in beam dynamics simulations.  
 
WEPP087 Observation and Mitigation of Multipass BBU in CEBAF linac, dipole, recirculation, optics 2722
 
  • R. Kazimi, A. Freyberger, C. Hovater, G. A. Krafft, F. Marhauser, T. E. Plawski, C. E. Reece, J. S. Sekutowicz, C. Tennant, M. G. Tiefenback, H. Wang
    Jefferson Lab, Newport News, Virginia
  The CEBAF recirculating accelerator at Jefferson Lab consists of two linacs carrying beam for up to five passes of acceleration. The Beam Break-Up (BBU) phenomenon was anticipated during design of the accelerator. The threshold beam current to induce BBU was calculated to be approximately 20 milliamperes, far above operational current. No sign of BBU was ever seen in more than a decade of operation. A specially designed acceleration cavity in a recently installed cryomodule was found to cause a BBU instability under special conditions with as low as 40 uA of injected beam current. This presented an opportunity to study BBU in a five-pass accelerator. In this paper we will discuss multipass BBU, show observational data, and discuss the ways we have developed to maintain the instability threshold current to values above those required for operation.  
 
WEPP089 Wake-field Suppression in the CLIC Main Linac dipole, coupling, emittance, positron 2725
 
  • V. F. Khan, R. M. Jones
    UMAN, Manchester
  The CLIC linear collider aims at accelerating multiple bunches of electrons and positrons and colliding at a centre of mass energy of 3 TeV. These bunches are accelerated through X-band linacs operating at an accelerating frequency of 12 GHz. Each beam readily excites wake-fields in the accelerating cavities of each linac. The transverse components of the wake-fields, if left unchecked, can dilute the beam emittance. The present CLIC design relies on heavy damping of these wake-fields in order to ameliorate the effects of the wake-field on the beam emittance. Here we present initial results on a modified design which combines both damping and detuning of the cell frequencies of each cavity structure in order to enhance the overall decay of the wake-field. Interleaving of cell frequencies is explored as a means to improve the damping.  
 
WEPP102 Design of the ILC RTML Extraction Lines extraction, kicker, collimation, focusing 2752
 
  • S. Seletskiy, P. Tenenbaum, D. R. Walz
    SLAC, Menlo Park, California
  • N. Solyak
    Fermilab, Batavia, Illinois
  The Damping Ring to the Main Linac beamline (RTML) is equipped with three extraction lines (EL). Each EL can be used both for an emergency abort dumping of the beam and the tune-up continual train-by-train extraction. Two of the extraction lines are located downstream of the first and second stages of the RTML bunch compressor, and must accept both compressed and uncompressed beam with energy spread of 2.5 % and 0.15 % respectively. In this paper we report optical design that allowed us to minimize the length of the extraction lines while offsetting the beam dumps from the main line by the distance required for acceptable radiation level in the service tunnel. Proposed extraction lines can accommodate beams with different energy spreads at the same time providing the beam size suitable for the aluminum dump window.  
 
WEPP151 Metallic Photonic Band Gap Accelerator Structure Experiments and Design vacuum, radiation, electron, insertion 2841
 
  • R. A. Marsh, M. A. Shapiro, R. J. Temkin
    MIT/PSFC, Cambridge, Massachusetts
  Damping wakefields is a critical issue in the next generation of high gradient accelerators. Photonic bandgap (PBG) structures have unique properties that offer significant wakefield damping. The goal of this work is to quantify the higher order mode (HOM) wakefield content of a constructed metallic PBG accelerator structure, in order to test the theory of wakefield excitation in these structures and to provide direction for future structure design. Experimental measurements of wakefields excited by an 18 MeV electron beam in a 6 cell, 17.14 GHz metallic PBG traveling wave accelerator structure are reported. Because the electron beam used to generate wakefields in the PBG structure is bunched at the 17.14 GHz rf frequency, all wakefields observed were at integer multiples of 17.14 GHz. Using diode detectors, radiation has been observed at the input and output coupler ports as well as through a quartz window in the surrounding vacuum vessel. Estimates of wakefield radiation, made using HFSS and basic wakefield theory, compare well with experiment.  
 
WEPP155 Laser Driven Linear Collider laser, acceleration, collider, plasma 2850
 
  • A. A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  We continue detailed description of scheme allowing long term acceleration with >10 GeV/m in multi-cell microstructures side-illuminated by laser radiation. The basis of the scheme is a fast sweeping device for the laser bunch. After sweeping the laser bunch has a slope ~45° with respect to the direction of propagation. So the every cell of microstructure becomes excited locally only for the moments, when the particles are there. Self consistent parameters of collider based on this idea allow consideration this type of collider as a candidate for the near-future accelerator era.  
 
WEPP164 Beam Collimation Studies for the ILC Positron Source collimation, positron, emittance, target 2871
 
  • A. I. Drozhdin
    Fermilab, Batavia, Illinois
  • Y. Nosochkov, F. Zhou
    SLAC, Menlo Park, California
  The results of collimation studies for the ILC positron source beam line are presented. The calculations of primary positron beam loss are done using the ELEGANT code. The secondary positron and electron beam loss, synchrotron radiation along the beam line and bremsstrahlung radiation in the collimators are simulated using the STRUCT code. The first part of the system, located right after the positron source target at 0.125 GeV, is used for protection of super-conducting RF Linac from heating and radiation. The second part of the system is used for final collimation of the beam before injection to the Damping Ring at 5 GeV. The calculated power loss in the collimation region is about 100 W/m, with loss in the collimators of 0.2-5 kW. The beam transfer efficiency from target to the Damping Ring is 13.5%.  
 
THXM01 CLIC Accelerating Structure Development site, collider, simulation, linac 2922
 
  • W. Wuensch
    CERN, Geneva
  One of the most important objectives of the CLIC (Compact Linear Collider) study is to demonstrate the design accelerating gradient of 100 MV/m in a fully featured accelerating structure under nominal operating conditions including pulse length and breakdown rate. The development and testing program which has been put into place to achieve this objective is described. Recent advances in understanding and quantifying the effects which limit the accelerating gradient are presented.  
slides icon Slides  
 
THXM03 Status of the European HOM Damped Normal Conducting Cavity impedance, vacuum, brilliance, simulation 2932
 
  • E. Weihreter
    BESSY GmbH, Berlin
  Cavities with damped higher order modes (HOMs) are an essential ingredient for state of the art storage ring based high brilliance synchrotron radiation sources to avoid degradation of the beam quality due to coupled bunch instabilities. Starting with a review of the concepts of existing HOM damped cavities the status of a normal conducting 500 MHz cavity is presented which has been developed for low and medium energy high brilliance synchrotron light sources within the frame of an EC funded collaboration. The results of numerical simulations and of low power impedance measurements are reported together with conceptional improvements, expected performance, and first operational achievements in the Metrology Light Source in Berlin.  
slides icon Slides  
 
THPPGM04 SLIM - An Early Work Revisited radiation, closed-orbit, coupling, lattice 2963
 
  • A. Chao
    SLAC, Menlo Park, California
  An early, but at the time illuminating, piece of work on how to deal with a general, linearly coupled accelerator lattice is revisited. This work is based on the SLIM formalism developed in 1979-1981.  
slides icon Slides  
 
THPC055 Dynamic Aperture Studies for PETRA III Including Magnet Imperfections multipole, wiggler, dynamic-aperture, lattice 3107
 
  • A. Kling, K. Balewski, W. Decking
    DESY, Hamburg
  • Y. J. Li
    BNL, Upton, New York
  PETRA III is a 3rd generation synchrotron radiation light source. Efficient injection in the top up mode requires a dynamic aperture of 30 mmmrad or larger, while a 2 hour Touschek lifetime needs an average momentum aperture of around 1.5 %. We present studies on the impact of recently measured magnet imperfections on the available dynamic aperture. To this end, tracking simulations have been performed including the effects of measured multipole errors of lattice magnets and of 20 four-meters-long damping wigglers.  
 
THPC113 Feedback Damper System for Quadrupole Oscillations after Transition at RHIC feedback, quadrupole, emittance, heavy-ion 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.  
 
THPC121 LHC Transverse Feedback System and its Hardware Commissioning kicker, feedback, injection, vacuum 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 pick-up, kicker, feedback, betatron 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.  
 
THPC126 Performance and Features of the Diamond TMBF System feedback, controls, single-bunch, pick-up 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 feedback, injection, kicker, betatron 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 feedback, storage-ring, acceleration, controls 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.

 
 
THPC132 Bunch by bunch Transverse Feedback Development at ESRF feedback, kicker, storage-ring, ion 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.  
 
THPC136 Design and Commissioning of a Bunch by Bunch Feedback System for the Australian Synchrotron feedback, kicker, synchrotron, storage-ring 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.  
 
THPP113 Emittance Growth at LHC Injection from SPS and LHC Kicker Ripple injection, kicker, emittance, feedback 3629
 
  • B. Goddard, M. J. Barnes, L. Ducimetière, W. Höfle, G. Kotzian
    CERN, Geneva
  Fast pulsed kicker magnets are used to extract beams from the SPS and inject them into the LHC. The kickers exhibit time-varying structure in the pulse shape which translates into small offsets with respect to the closed orbit at LHC injection. The LHC damper systems will be used to damp out the resulting betatron oscillations, to keep the growth in the transverse emittance within specification. This paper describes the results of the measurements of the kicker ripple for the two systems, both in the laboratory and with beam, and presents the simulated performance of the transverse damper in terms of beam emittance growth. The implications for LHC operation are discussed.  
 
THPP114 LHC Transverse Feedback Damping Efficiency feedback, injection, simulation, octupole 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.