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damping

      
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MOYCH03 Superconducting RF Cavities for Synchrotron Light Sources electron, storage-ring, insertion, synchrotron 21
 
  • P. Marchand
    SOLEIL, Gif-sur-Yvette
  Superconducting (sc) RF systems are already operational or planned in several third generation synchrotron light sources. In these machines, which require relatively low RF accelerating voltage and high beam loading, the advantage of using the sc technology essentially resides in the fact that one can achieve an efficient damping of the cavity Higher Order Modes (HOM) while still maintaining a high fundamental shunt impedance. The strong HOM damping practically is realised following two approaches : a) use of absorber material, located inside the cavity tube cut-off, through which the HOM propagate and then are damped (Cornell/KEK designs); b) two-cell cavity with coaxial HOM dampers located on the tube connecting the two cells (SOLEIL design). Third harmonic idle sc cavities (1.5 GHz) of the SOLEIL type are already operational in the Swiss Light Source and ELETTRA. The main RF system (500 MHz) of these machines consist of normal conducting cavities and the purpose of the third harmonic sc system is to lengthen the bunches in order to improve the beam lifetime and stability (additional Landau damping). Recently, several third generation synchrotron light sources have also planned to use sc cavities as main accelerating RF systems. The operational conditions of the existing systems as well as the status of the planned ones are reported here.  
Video of talk
Transparencies
 
MOPKF017 New Simulations on Microbunching Instability at TTF2 cathode, simulation, linac, space-charge 339
 
  • Y. Kim, Y. Kim, D. Son
    CHEP, Daegu
  • K. Floettmann
    DESY, Hamburg
  Microbunching instability in the FEL driver linac can be induced by collective self-fields such as longitudinal space charge, coherent synchrotron radiation, and geometric wakefields. In this paper, we describe the first start-to-end simulations including all important collective self-fields from the cathode to the end of TTF2 linac with 1.5 million macroparticles.  
 
MOPKF076 An Overview of the Cryomodule for the Cornell ERL Injector linac, emittance, coupling, synchrotron 491
 
  • H. Padamsee, B.M. Barstow, V. Medjidzade, V.D. Shemelin, K.W. Smolenski
    Cornell University, Ithaca, New York
  • I. Bazarov, C.K. Sinclair
    Cornell University, Department of Physics, Ithaca, New York
  • S.A. Belomestnykh, R. Geng, M. Liepe, M. Tigner, V. Veshcherevich
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  The first stage of the Cornell ERL project will be a 100 MeV, 100 mA (CW) prototype machine to study the energy recovery concept with high current, low emittance beams. In the injector, a bunched 100 mA, 500 keV beam of a DC gun will be compressed in a normal-conducting copper buncher and subsequently accelerated by five superconducting 2-cell cavities to an energy of 5.5 MeV. We will present an overview of the injector status to include the status of the cryomodule design along with the status of the 2-cell HOM-free cavity, the twin-input coupler and the ferrite HOM dampers in related papers.  
 
MOPKF081 Peak Current Optimization for LCLS Bunch Compressor 2 undulator, emittance, simulation, linac 506
 
  • A.C. Kabel, P. Emma
    SLAC, Menlo Park, California
  The performance of an FEL will be a function of both the driving bunch's current and its slice emittance. We have studied a set of parameters for the bunch compression section of the LCLS, simulating the effects of Coherent Synchrotron Radiation (CSR) on the slice emittance of the bunch core as a function of peak current. We use the code TraFiC4 for a three-dimensional, self-consistent simulation on parallel computers. While higher currents will increase FEL performance, its detrimental effects, due to CSR, on slice emittance will counteract this beneficial effect. From our simulations, we determine a near-optimum current, balancing these effects.  
 
MOPLT020 Limits to the Performance of the LHC with Ion Beams ion, luminosity, emittance, radiation 578
 
  • J.M. Jowett, H.-H. Braun, M.I. Gresham, E. Mahner, A.N. Nicholson, E.N. Shaposhnikova
    CERN, Geneva
  • I.A. Pshenichnov
    RAS/INR, Moscow
  The performance of the LHC as a heavy-ion collider will be limited by a diverse range of phenomena that are often qualitatively different from those limiting the performance with protons. We summarise the latest understanding and results concerning the consequences of nuclear electromagnetic processes in lead ion collisions, the interactions of ions with the residual gas and the effects of lost ions on the beam environment and vacuum. Besides these limitations on beam intensity, lifetime and luminosity, performance will be governed by the evolution of the beam emittances under the influences of synchrotron radiation damping, intra-beam scattering, RF noise and multiple scattering on residual gas. These effects constrain beam parameters in the LHC ring throughout the operational cycle with lead ions.  
 
MOPLT024 Flexibility, Tolerances, and Beam-Based Tuning of the CLIC Damping Ring coupling, betatron, closed-orbit, sextupole 590
 
  • M. Korostelev, J. Wenninger, F. Zimmermann
    CERN, Geneva
  The present design of the CLIC damping ring can easily accommodate anticipated CLIC parameter changes. Realistic misalignments of magnets and monitors increase the equilibrium emittance. In simulations we study both the sensitivity to magnet displacements and the emittance recovery achieved by orbit correction, dispersion-free steering and coupling compensation.  
 
MOPLT041 Production of Superconducting Accelerator Modules for High Current Electron Storage Rings storage-ring, vacuum, instrumentation, electron 638
 
  • M. Pekeler, S. Bauer, B. Griep, M. Knaak, H.P. Vogel, P. vom Stein
    ACCEL, Bergisch Gladbach
  For Diamond Light Source, ACCEL was awarded to produce three more superconducting 500 MHz accelerator modules of the Cornell CESR design. With the already 6 modules produced for Cornell, NSRRC and CLS, this module can now be considered as a kind of standard product. In this paper we describe the basic parameters and guaranteed values of this module and will also report on the performance of delivered modules.  
 
MOPLT090 High Pulse and Average Power Low-induction Load injection, linac, extraction, storage-ring 746
 
  • F.V. Podgorny, B.I. Grishanov
    BINP SB RAS, Novosibirsk
  A high pulse and average power low-induction load with a built-in divider is described in this report. The load has a nominal resistance of 25 Ohm and is designed to operate with a repetition rate of up to 50 Hz at a pulse duration (FWHM) of 100 ns, a rise/fall time of 50 ns and a pulse amplitude of up to 40 kV. In this mode the dissipated energy is equal to about 8 J per pulse and average power is up to 400 W. The load can be used as an absorbing load and as a block element in high-voltage engineering.  
 
MOPLT092 Single Mode RF Cavity for VEPP-2000 Storage Ring Based Collider coupling, storage-ring, impedance, luminosity 752
 
  • V. Volkov, A. Bushuev, E. Kenjebulatov, I. Koop, A. Kosarev, Ya.G. Kruchkov, S.A. Krutikhin, I. Kuptcov, I. Makarov, N. Mityanina, V. Petrov, E. Rotov, I. Sedlyarov, Y.M. Shatunov
    BINP SB RAS, Novosibirsk
  Accelerating cavity 172 MHz with strong damped higher-order modes (HOM) for VEPP-2000 electron-positron collider have been made in Novosibirsk. Resonance frequences and Q values of cavity HOMs are measured and analysed. Most of HOMs have Q values less than 300. We compare these results with computer calculations of HOM.  
 
MOPLT122 Dynamical Aperture Study for the NLC Main Damping Rings wiggler, dynamic-aperture, lattice, octupole 824
 
  • M. Venturini, S. Marks, A. Wolski
    LBNL, Berkeley, California
  A sufficiently large acceptance is critical for the NLC Main Damping Rings (MDR) as the high power carried by the beams demands very high injection efficiency. Both chromatic sextupoles and wiggler insertions, needed for damping, are substantial sources of nonlinearities limiting the dynamical aperture. We report on our latest studies on single particle dynamics for the MDR current lattice with and without inclusion of lattice errors and with attention paid to working point optimization. The possibility to use octupole magnets for compensation is also explored.  
 
MOPLT123 A Reduced Emittance Lattice for the NLC Positron Pre-damping Ring lattice, wiggler, emittance, injection 827
 
  • I. Reichel, A. Wolski
    LBNL, Berkeley, California
  The Pre-Damping Ring of the Next Linear Collider has to accept a large positron beam from the positron production target, and reduce the emittance and energy spread to low enough values for injection into the Main Damping Ring. A previous version of the lattice yielded an emittance of the extracted beam which was about 20% too large. In order to get the emittance down to the required value the quadrupole magnets in the dispersive regions in the ring were moved horizontally; this modifies the damping partition numbers. In addition, the model of the wigglers has been modified to reflect more closely the magnetic field map. The new lattice design meets damping and emittance requirements. The lattice and dynamic aperture studies are presented.  
 
MOPLT131 Emittance Dilution Simulations for Normal Conducting and Superconducting Linear Colliders emittance, linac, simulation, collider 845
 
  • R.M. Jones, T.O. Raubenheimer
    SLAC, Menlo Park, California
  • N. Baboi
    DESY, Hamburg
  An electron (or positron) multi-bunch train traversing several thousand accelerator structures can be distorted by long-range wakefields left behind the accelerated bunches. These wakefields can at the very least, give rise to a dilution in the emittance of the beam and, at worst can lead to a beam break up instability. We investigate the emittance dilution that occurs for various frequency errors (corresponding to small errors made in the design or fabrication of the structure) for the GLC/NLC (Global Linear Collider/Next Linear Collider) and for TESLA (Terra Electron Superconducting Linear Accelerator). Resonant effects, which can be particularly damaging, are studied for X-band and L-band linacs. Simulations are performed with the computer codes LIAR[1] and L-MAFIA[2].

[1] R. Assman et al, LIAR, SLAC-PUB AP-103[2] The MAFIA Collaboration, MAFIA: L - The Linear Accelerator Tracking Code, CST GmbH, Darmstadt (1994)

 
 
MOPLT134 X-Band Linear Collider R&D in Accelerating Structures through Advanced Computing simulation, collider, impedance, linear-collider 851
 
  • Z. Li, N.T. Folwell, L. Ge, A. Guetz, V. Ivanov, K. Ko, M. Kowalski, L. Lee, C.-K. Ng, G. Schussman, R. Uplenchwar
    SLAC, Menlo Park, California
  • M. Wolf
    University of Illinois, Urbana
  The X-band linear collider design, GLC/NLC, requires accelerating structures in the main linac to operate at 65 MV/m and to be able to control emittance growth due to dipole wakefields generated by 100 micron bunch trains. The approach to high gradient has focused mainly on testing structures for acceptable breakdown rates at the desired gradient through experiments since the problem is analytically challenging. In suppressing dipole wakefields, the damped, detuned structure (DDS) has shown capable of meeting design requirements but the analysis using equivalent circuits has thus far been limited to the lowest two dipole bands. This paper describes a computational approach that addresses these design issues through large-scale simulations, using a suite of parallel electromagnetic codes developed under the DOE SciDAC Accelerator Simulation Project. Numerical results on peak field calculation, dark current generation, and wakefield computation will be presented on the H60VG4S17 DDS structure, considered to be the baseline design for the NLC.  
 
MOPLT135 Damping the High Order Modes in the Pumping Chamber of the PEP-II Low Energy Ring positron, vacuum, impedance, electromagnetic-fields 854
 
  • A. Novokhatski, S. Debarger, F.-J. Decker, A. Kulikov, J. Langton, M. Petree, J. Seeman, M.K. Sullivan
    SLAC, Menlo Park, California
  The Low Energy Ring of the PEP-II B-factory operates with extremely high currents and short positron bunches. Any discontinuity in the vacuum chamber can excite a broad-band spectrum of the High Order Modes. A temperature rise has been found in the vacuum chamber elements in one transition from straight section to arc. The power in the wake fields was high enough to char beyond use the feed-through for the Titanium Sublimation Pump. This pumping section consists of the beam chamber and an ante-chamber. Fields, excited in the beam chamber penetrate to the ante-chamber and then through the heater wires of the TSP come out. A small ceramic tile was placed near the TSP feed-through to absorb these fields. A short wire antenna was also placed there. HOM measurements show a wide spectrum with a maximum in the 2-3 GHz region. A special water cooled HOM absorber was designed and put inside the ante-chamber part of the section. As a result, the HOM power in the section decreased and the temperature rise went down. The power loss is 750 W for a beam current of 2 A. Measurements of the HOM impedance for different bunch patterns, bunch length and transverse beam position will be presented.  
 
MOPLT155 Study of Beam-beam Effects at PEP-II luminosity, simulation, positron, coupling 896
 
  • I.V. Narsky, F.C. Porter
    CALTECH, Pasadena, California
  • Y. Cai, J. Seeman
    SLAC, Menlo Park, California
  • W. Kozanecki
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  Using a self-consistent, three-dimensional simulation program running on parallel supercomputers, we have simulated the beam-beam interaction at the PEP II asymmetric e+e- collider. In order to provide guidance to luminosity improvement in PEP-II, we have scanned the tunes and other machine parameters in both rings, and computed their impact on the luminosity and particle loss. Whenever possible, the code has been benchmarked against experimental measurements, at various beam currents, of luminosity and luminous-region size using the BaBar detector. These studies suggest that three-dimensional effects such as bunch lengthening may be important to understand a steep drop of luminosity near the peak currents.  
 
MOPLT159 RF Techniques for Improved Luminosity at RHIC resonance, emittance, booster, luminosity 905
 
  • J.M. Brennan, M. Blaskiewicz, J. Butler, J. DeLong, W. Fischer, T. Hayes
    BNL, Upton, Long Island, New York
  The Relativistic Heavy Ion Collider has improved its luminosity performance significantly in the course of the first three physics runs. A number of special techniques for the operation of the rf systems have been developed to facilitate these improvements. Herein we describe these techniques, which include: an ultra low-noise rf source for the 197 MHz storage cavities; synchronization of the two rings during acceleration (including crossing the transition energy) to avoid spurious collisions on the ramp, which modulate the beam-beam tune shift; a frequency shift switch-on technique for transferring bunches from the acceleration to the storage rf systems; installation of dedicated 200 MHz cavities to provide longitudinal Landau damping on the ramp, and automated corrections to longitudinal injection parameters to minimize emittance growth.  
 
TUPKF001 Upgrade and Commissioning of the LNLS RF System storage-ring, klystron, synchrotron, feedback 950
 
  • R.H.A. Farias, N.P. Abreu, L.C. Jahnel, L. Liu, C. Pardine, P.F. Tavares
    LNLS, Campinas
  In this paper we present a report on the commissioning of the new RF system of the electron storage ring of the brazilian synchrotron radiation facility (LNLS).  
 
TUPKF011 First Tests of a HOM-Damped High Power 500MHz Cavity impedance, vacuum, simulation, coupling 979
 
  • F. Marhauser, E. Weihreter
    BESSY GmbH, Berlin
  A prototype high power 500 MHz copper cavity with three tapered circular waveguides for broadband higher order mode (HOM) damping has been fabricated especially for the use in 3rd generation synchrotron radiation sources. Low power impedance measurements are presented and compared with theoretical simulations to verify the expected HOM damping efficiency as well as the fundamental mode shunt impedance. After a careful cleaning and baking process to reduce the vacuum pressure the cavity has been conditioned at high power. All relevant parameters of the cavity are reported.  
 
TUPKF012 A HOM Damped Planar Accelerating Structure dipole, impedance, coupling, polarization 982
 
  • A. Blednykh, H. Henke
    TET, Berlin
  The problem of very fast higher order mode (HOM) suppression, in the order of 1ns, was investigated for a planar 30GHz accelerating structure. Both, damping and detuning were considered. A sufficient suppression could be achieved by damping waveguides in every cell in vertical and in horizontal direction. Finally, a scaled-up 10GHz model was built. It is a 35 cm long aluminum structure, which was machined by high-precision milling. In order to reduce the surface gradient on the input/output coupling irises a symmetrical RF coupler was developed. The HOM damping is accomplished by coupling six damping waveguides to each accelerating cell. The waveguides are loaded by a low resitivity RF load. The whole structure with waveguides and loads was optimized by means of the computer code GdfidL. The paper gives the design criteria and the results of s-parameter and bead-pull measurements.  
 
TUPKF021 First Year of Operation of SUPER-3HC at ELETTRA storage-ring, vacuum, electron, synchrotron 1009
 
  • G. Penco, P. Craievich, A. Fabris, C. Pasotti, M. Svandrlik
    ELETTRA, Basovizza, Trieste
  Since July 2003 a superconducting third harmonic cavity has been in routine operation at ELETTRA. When the cavity is activated the stored electron bunches are lengthened by about a factor of three. The related longitudinal Landau damping has allowed first time operation at 320 mA, 2.0 GeV with a beam completely free of longitudinal coupled bunch instabilities. With the cavity active the lifetime at 320 mA, 2.0 GeV is three times the theoretical value for nominal bunch length. The increase in beam stability and lifetime contributed significantly to enhance the brightness and the integrated flux of the source. We will further discuss the operating experience with the superconducting cavity and the cryogenic system, analyzing the impact of the new system on machine operation and uptime. Finally we will also report on the characterization of the cavity performance for different filling patterns of the storage ring and relate the results to preliminary beam-cavity interaction studies.  
 
TUPKF053 New Waveguide-type HOM Damper for the ALS Storage Ring RF Cavities storage-ring, vacuum, radiation, synchrotron 1069
 
  • S. Kwiatkowski, K.M. Baptiste, J. Julian
    LBNL/ALS, Berkeley, California
  The ALS storage ring 500 MHz RF system uses two re-entrant accelerating cavities powered by a single 320kW PHILLIPS YK1305 klystron. During several years of initial operation, the RF cavities were not equipped with effective passive HOM damper systems. Longitudinal beam stability was achieved through cavity temperature control and the longitudinal feedback system (LFB), which was often operating at the edge of its capabilities. As a result, longitudinal beam stability was a significant operations issue at the ALS. During two consecutive shutdown periods (April 2002 and 2003) we installed E-type HOM dampers on the main and third harmonic cavities. These devices dramatically decreased the Q-values of the longitudinal anti-symmetric HOM modes. The next step is to damp the rest of the longitudinal HOM modes in the main cavities below the synchrotron radiation damping level. This will hopefully eliminate the need for the LFB and set the stage for a possible increase in beam current. The ?waveguide? type of HOM damper was the only option that didn?t significantly compromise the vacuum performance of the RF cavity. The design process and the results of the low level measurements of the new waveguide dampers are presented in this paper.  
 
TUPKF061 The SPEAR3 RF System klystron, feedback, radiation, impedance 1084
 
  • P.A. McIntosh, S. Allison, P. Bellomo, S. Hill, V. Pacak, S. Park, J.J. Sebek, D.W. Sprehn
    SLAC, Menlo Park, California
  SPEAR2 was upgraded in 2003, to a new 3rd Generation Light Source (3GLS) enabling users to take better advantage of almost 100x higher brightness and flux density over its predecessor SPEAR2. As part of the upgrade, the SPEAR2 RF system has been re-vamped from its original configuration of one 200 kW klystron feeding a single 358.5 MHz, 5-cell aluminum cavity; to a 1.2 MW klystron feeding four 476.3 MHz, HOM damped copper cavities. The system installation was completed in late November 2003 and the required accelerating voltage of 3.2 MV (800 kV/cavity) was very rapidly achieved soon after. This paper details the SPEAR3 RF system configuration and its new operating requirements, highlighting its installation and subsequent successful operation.  
 
TUPKF062 PEP-II RF System Operation and Performance klystron, feedback, luminosity, impedance 1087
 
  • P.A. McIntosh, J. Browne, J.E. Dusatko, J.D. Fox, W.C. Ross, D. Teytelman, D. Van Winkle
    SLAC, Menlo Park, California
  The Low Energy Ring (LER) and High Energy Ring (HER) RF systems have operated now on PEP-II since July 1998 and have assisted in breaking all design luminosity records back in June 2002. Luminosity on PEP-II has steadily increased since then as a consequence of larger e+ and e- beam currents being accumulated. This has meant that the RF systems have inevitably been driven harder, not only to achieve these higher stored beam currents, but also to reliably keep the beams circulating whilst at the same time minimizing the number of aborts due to RF system faults. This paper details the current PEP-II RF system configurations for both rings, as well as future upgrade plans spanning the next 3-5 years. Limitations of the current RF system configurations are presented, highlighting improvement projects which will target specific areas within the RF systems to ensure that adequate operating overheads are maintained and reliable operation is assured.  
 
TUPKF072 Production and Performance of the CEBAF Upgrade Cryomodule Intermediate Prototypes linac, vacuum, controls, synchrotron 1105
 
  • A-M. Valente, E. Daly, J.R. Delayen, M. Drury, R. Hicks, C. Hovater, J. Mammosser, H.L. Phillips, T. Powers, J.P. Preble, C. Reece, R.A. Rimmer, H. Wang
    Jefferson Lab, Newport News, Virginia
  • C. Thomas-Madec
    SOLEIL, Gif-sur-Yvette
  We have installed two new cryomodules, one in the nuclear physics accelerator (CEBAF) and the other in the Free Electron Laser (FEL) of Jefferson Lab. The new cryomodules consist of 7-cell cavities with the original CEBAF cell shape and were designed to deliver gradients of 70 MV/module. Several significant design innovations were demonstrated in these cryomodules. This paper describes the production procedures, the performance characteristics of these cavities in vertical tests, results of tests in the new cryomodule test facility (CMTF) as well as the commissioning in the CEBAF tunnel and FEL. Performances and limitations after installation in the accelerators are discussed in this paper along with improvements proposed for future cryomodules.  
 
TUPLT036 Optimization of Low Emittance Lattices for PETRA III lattice, wiggler, sextupole, emittance 1225
 
  • W. Decking, K. Balewski
    DESY, Hamburg
  The reconstruction of the existing 2.3 km long storage ring PETRA II into a 3rd generation synchrotron light source (PETRA III) calls for an horizontal emittance of 1 nm rad. In addition the on- and off-momentum dynamic acceptance should be large to ensure sufficient injection efficiency and beam lifetime. We present three different types of lattices for the arcs of PETRA: a so-called TME lattice and a FODO lattice which both are newly designed to reach the specified emittance and the present FODO lattice with damping wigglers. The different lattice types have been compared through tracking calculations, including wiggler nonlinearities. Only the relaxed FODO lattice with damping wigglers meets the acceptance goals.  
 
TUPLT163 Achieving Beam Quality Requirements for Parity Experiments at Jefferson Lab feedback, electron, polarization, target 1509
 
  • Y.-C. Chao, H. Areti, F.J. Benesch, B. Bevins, S.A. Bogacz, S. Chattopadhyay, J.M. Grames, J. Hansknecht, A. Hutton, R. Kazimi, L. Merminga, M. Poelker, Y. Roblin, M. Tiefenback
    Jefferson Lab, Newport News, Virginia
  • D. Armstrong
    The College of William and Mary, Williamsburg
  • D. Beck, K. Nakahara
    University of Illinois, Urbana
  • K. Paschke
    University of Massachusetts, Amherst
  • M. Pitt
    Virginia Polytechnic Institute and State University, Blacksburg
  Measurement of asymmetry between alternating opposite electron polarization in electron-nucleon scattering experiments can answer important questions about nucleon structures. Such experiments impose stringent condition on the electron beam quality, and thus the accelerator used for beam creation and delivery. Of particular concern to such ?parity? experiments is the level of correlation between beam characteristics (orbit, intensity) and electron polarization that can obscure the real asymmetry. This can be introduced at the beam forming stage, created due to scraping, or not damped to desired level due to defective transport. Suppression of such correlation thus demands tight control of the beam line from cathode to target, and requires multi-disciplined approach with collaboration among nuclear physicists and accelerator physicists/engineers. The approach adopted at Jefferson Lab includes reduction of correlation source, improving low energy beam handling, and monitoring and correcting global transport. This paper will discuss methods adopted to meet the performance criteria imposed by parity experiments, and ongoing research aimed at going beyond current performance.  
 
WEOALH01 Particle-in-cell Beam Dynamics Simulations simulation, electromagnetic-fields, cathode, space-charge 170
 
  • T. Lau, E. Gjonaj, T. Weiland
    TEMF, Darmstadt
  We describe the application of the Conformal Finite Integration Technique (CFIT) in the time-domain to beam dynamics simulations with the Particle-In-Cell (PIC) method. The conformal method results in a more accurate field solution for complicated geometries than the traditional FIT approach. For long-time simulations we investigate several methods for the suppression of the spurious noise, typically emerging in PIC simulations. The results are compared with the analytical solution for a bunch in a semi-infinite waveguide for each of the presented methods. As a realistic example simulations for the RF-Gun installed at Photo Injector Test Facility in DESY Zeuthen (PITZ) will be presented.  
Video of talk
Transparencies
 
WEPKF080 Secondary Electron Yield Measurements from Thin Surface Coatings for NLC Electron Cloud Reduction electron, vacuum, luminosity, positron 1789
 
  • F. Le Pimpec, F. King, R.E. Kirby, M.T.F. Pivi
    SLAC, Menlo Park, California
  In the beam pipe of the positron damping ring of the Next Linear Collider, electrons will be created by beam interaction with the surrounding vacuum chamber wall and give rise to an electron cloud. Several solutions are possible for avoiding the electron cloud, without changing the beam bunch structure or the diameter of the vacuum chamber. Some of the currently available solutions include reducing residual gas ionization by the beam, minimizing photon-induced electron production, and lowering the secondary electron yield (SEY) of the chamber wall. We will report on recent SEY measurements performed at SLAC on TiN coatings and TiZrV non-evaporable getter thin films.  
 
WEPLT030 Stability Diagrams for Landau Damping with Two-dimensional Betatron Tune Spread from Both Octupoles and Non-linear Space Charge applied to the LHC at Injection space-charge, octupole, betatron, injection 1897
 
  • E. Métral, F. Ruggiero
    CERN, Geneva
  The joint effect of space-charge non-linearities and octupole lenses is discussed for the case of a quasi-parabolic transverse distribution of a monochromatic beam. The self-consistent non-linear space-charge tune shift corresponding to the above distribution function is first derived analytically. The exact dispersion relation is also given but not solved. Instead, noting that a good approximation of the non-linear space-charge tune shift is obtained considering only linear terms in the action variables, the dispersion relation is solved analytically in this approximate case. As expected, in the absence of external (octupolar) non-linearities, the result of Möhl and Schönauer is recovered: there is no stability region. In the absence of space charge, the stability diagrams of Berg and Ruggiero are also recovered. Finally, the new result is applied to the LHC at injection.  
 
WEPLT041 RF Amplitude Modulation to Suppress Longitudinal Coupled Bunch Instabilities in the SPS synchrotron, proton, impedance, pick-up 1924
 
  • E. Vogel, T. Bohl, U. Wehrle
    CERN, Geneva
  In the SPS, even after a considerable impedance reduction including the removal of all RF cavities used for lepton acceleration in the past, longitudinal coupled bunch instabilities develop with an LHC beam of about one fifth of the nominal bunch intensity. The nominal LHC beam is stabilised using both, the 800 MHz Landau damping cavities, in bunch shortening mode, and pre-emptive emittance blow-up. An alternative method to increase the synchrotron frequency spread and thus stabilise the beam is amplitude modulation of the accelerating RF voltage. This method might be especially suitable in accelerators without a higher harmonic RF system, as will be the case in LHC. The main results of recent studies using this method in the SPS and considerations about its use in LHC are presented.  
 
WEPLT063 Investigation of Cavity Induced Longitudinal Coupled Bunch Mode Instability Behaviour and Mechanisms synchrotron, storage-ring, simulation, radiation 1990
 
  • R.G. Heine, P. Hartmann, H. Huck, G. Schmidt, T. Weis
    DELTA, Dortmund
  The narrowband impedances of RF-resonators in a circular accelerator can drive coupled bunch mode - CBI - instabilities which might spoil the overall beam quality. Often, as in synchrotron radiation light sources e.g. the instability does not lead to beam loss but to a severe degradation of the source brilliance. Investigations of longitudinal CBIs have been performed at the DELTA storage ring with a single DORIS-type cavity for future comparision with the behaviour of a HOM-damped cavity to be tested at DELTA. This resonator is presently developed and built within an EU-collaboration. The beam was deliberately driven into instability using the beam current as well as the cavity temperature as individual parameters. The instability characterisations at low (542 MeV) and high (1,5 GeV) energy exhibit a complex behaviour. The strength of the instability measured by the bunch excursions in the case of longitudinal CBIs, but also the spreading of the instability across neighbouring modes depends on parameters such as beam energy, resonant impedance but also on counteracting mechanisms like synchrotron radiation and Landau damping. The paper will cover the experimental results together with estimations of the influence and mechanism of Landau damping.  
 
WEPLT066 Beam Dynamics Study for PETRA III Including Damping Wigglers wiggler, undulator, lattice, dynamic-aperture 1999
 
  • Y.L. Li, K. Balewski, W. Decking
    DESY, Hamburg
  Damping wigglers will be installed in the storage ring PETRA III to control the beam emittance to 1 nmrad. These wigglers will produce linear and nonlinear perturbations on beam dynamics. A new expanded transport matrix method is developed to solve linear dynamics, and used to match linear lattice functions. The symplectic method is adopted to track particle through the whole ring including the damping wigglers. Halbach?s formulae are used to describe the wiggler field. The main parameters of the wigglers are derived from field calculations. In order to avoid dangerous resonances, tune scanning is implemented to find suitable working points. According to presently known field quality, the nonlinear effects of damping wigglers will not degrade the performance of PETRA III and the dynamic aperture is still larger than the physical aperture.  
 
WEPLT092 Equilibrium Longitudinal Distribution for Localized Regularized Inductive Wake synchrotron, radiation, radio-frequency, vacuum 2065
 
  • S. Petracca, T. Demma
    U. Sannio, Benevento
  • K. Hirata
    GUAS, Kanagawa
  In a recent paper [*] we have shown that a localized wake assumption and the Gaussian approximation for the longitudinal beam distribution function can be used to understand the nature of the stationary solutions for the inductive wake, by comparison between the resulting map and the Haissinski equation, which rules the (less realistic) case of a uniformly distributed wake. In particular we showed the non-existence of solutions of Haissinski's equation when the inductive wake strength exceeds a certain threshold [**] to correspond to the onset of chaos in the map evolving the moments of the beam distribution from turn to turn. In this paper we use the same formalism to confirm that as noted in [**] for Haissinski's equation, a steady state solution for the longitudinal phase space distribution function always exists if a physically regularized inductive wake, which satisfies an obvious causality condition, is used.

* S. Petracca and Th. Demma, Proc. of the 2003 PAC, IEEE Press, New York, 2003, ISBN 0-7803-7739-9, p.2996.** Y. Shobuda and K. Hirata, Part. Accel. vol. 62, 165 (1999).

 
 
WEPLT122 Investigation of Microwave Instability on Electron Storage Ring TLS impedance, simulation, single-bunch, storage-ring 2140
 
  • M.-H. Wang
    NSRRC, Hsinchu
  • A. Chao
    SLAC, Menlo Park, California
  With the planned installation of a superconducting rf system, the new operation mode of TLS, the electron storage ring at NSRRC, is expected to double the beam intensity. Several accelerator physics topics need to be examined. One of these topics concerns the beam instability of single-bunch longitudinal microwave instability. We consider different approaches to measure the effective broad band impedance. We compare these measurement results with each other and to the old data [*]. The new measurements of effective broad band impedance are higher than the old measurement since between these two sets of measurements several narrow gap insertion devices were installed into the storage ring. We calculate the threshold current of microwave instability with a mode-mixing analysis code written by Dr. K. Oide of KEK [**]. We also develop a multi-particle tracking code to simulate the instability. The results of simulation and measurement are compared and discussed. We conclude that the doubling of beam current will not onset the microwave instability even without a Landau cavity to lengthen the bunch.

* M.H. Wang, et al.,"Longitudinal Beam Instability Observation with streak Camera at SRRC", proceeding of 1996 European Particle Accelerator Conference, pp. 1120** K. Oide, "Longitudinal Single-Bunch Instability in Electron Storage Rings", KEK Preprint 90-10

 
 
WEPLT137 Higher Order Modes in the New 100 and 500 MHz Cavities at MAX-lab synchrotron, synchrotron-radiation, coupling, impedance 2158
 
  • H. Tarawneh, Å. Andersson, M. Bergqvist, M. Brandin, M. Eriksson, L. Malmgren
    MAX-lab, Lund
  The MAX-II electron storage ring operates exclusively in multi-bunch mode with all buckets filled. Damping of the longitudinal higher order mode (HOM) instabilities has successfully been provided by passive third harmonic 1.5 GHz cavities. With a new RF employing three 100 MHz capacity loaded cavities and a fifth harmonic Landau cavity installed, a study of the HOM impedances, and related threshold instability currents, is necessary. Measurements and calculations so far, are being presented.  
 
WEPLT138 Laser Cooling of Electron Bunches in Compton Storage Rings laser, synchrotron, emittance, electron 2161
 
  • E.V. Bulyak
    NSC/KIPT, Kharkov
  Self-consistent dynamics of a bunch circulating in the Compton storage ring has been studied analytically. Disturbances from both the synchrotron and Compton radiations were taken into account. The emittances in laser-dominated rings (where the synchrotron energy losses are much smaller then the Compton ones) were evaluated. The resultant emittances (synchrotrons plus Comptons) were compared with the synchrotrons. As were shown, the longitudinal degree of freedom is heated up due to Compton scattering. Almost the same conclusion is valid for the vertical uncoupled betatron emittance. Since it is impossible in principle to get zero dispersion in the banding magnets, the radial emittance almost always cooling down by laser. Therefore in practical cases of coupled transverse oscillations with the horizontal emittance determining the vertical one, the laser will cool down the transverse degrees of freedom.  
 
WEPLT153 Multi-pass Beam-breakup: Theory and Calculation linac, simulation, recirculation, injection 2197
 
  • I. Bazarov
    Cornell University, Department of Physics, Ithaca, New York
  • G. Hoffstaetter
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  Multi-pass, multi-bunch beam-breakup (BBU) has been long known to be a potential limiting factor for the current in linac-based recirculating accelerators. New understanding of theoretical and computational aspects of the phenomenon are presented here. We also describe a detailed simulation study of BBU in the proposed 5 GeV Energy Recovery Linac light source at Cornell University which is presented in a separate contribution to this conference.  
 
WEPLT158 Direct Measurement of the Resistive Wakefield in Tapered Collimators linac, vacuum, impedance, electron 2212
 
  • P. Tenenbaum
    SLAC, Menlo Park, California
  • D. Onoprienko
    Brunel University, Middlesex
  The transverse wakefield component arising from surface resistivity is expected to play a major role in the beam dynamics of future linear colliders. We report on a series of experiments in which the resistive wakefield was measured in a series of tapered collimators, using the Collimator Wakefield beam test facility at SLAC. In order to separate the contributions of geometric and resistive wakefields, two sets of collimators with identical geometries but different resistivities were measured. The results are in agreement with the theoretical prediction for the high-resistivity (titanium) collimators, but in the case of low-resistivity (copper) collimators the resistive deflections appear to be substantially larger than predicted.  
 
WEPLT159 Linear Vlasov Analysis for Stability of a Bunched Beam synchrotron, storage-ring, synchrotron-radiation, coupling 2215
 
  • R.L. Warnock, G.V. Stupakov
    SLAC, Menlo Park, California
  • J.A. Ellison
    UNM, Albuquerque, New Mexico
  • M. Venturini
    LBNL, Berkeley, California
  We study the linearized Vlasov equation for a bunched beam subject to an arbitrary wake function. Following Oide and Yokoya, the equation is reduced to an integral equation expressed in angle-action coordinates of the distorted potential well. Numerical solution of the equation as a formal eigenvalue problem leads to difficulties, because of singular eigenmodes from the incoherent spectrum. We rephrase the equation so that it becomes non-singular in the sense of operator theory, and has only regular solutions for coherent modes. We report on a code that finds thresholds of instability by detecting zeros of the determinant of the system as they enter the upper-half frequency plane, upon increase of current. Results are compared with a time-domain integration of the nonlinear Vlasov equation, and with experiment, for a realistic wake function for the SLC damping rings.  
 
THPKF019 PETRA III: A New High Brilliance Synchrotron Radiation Source at DESY wiggler, undulator, emittance, insertion 2302
 
  • K. Balewski, W. Brefeld, W. Decking, Y.L. Li, G.K. Sahoo, R. Wanzenberg
    DESY, Hamburg
  DESY has decided to rebuild its 2304 m long accelerator PETRA II into a dedicated light source called PETRA III. The reconstruction is planned to start mid of 2007.The new light source will operate at an energy of 6 GeV, a current of 100 mA, a horizontal emittance of 1 nmrad and an emittance coupling of 1%. In the first phase thirteen insertion devices are foreseen. In this paper the principle layout of the machine will be presented. The structure of the new machine combines properties of conventional storage rings and light sources and is therefore quite unconventional. One of the major challenges of the project is to achieve the small emittances. The basic idea is to use so called damping wigglers with a total length of 80 m to reduce the horizontal emittance to the desired level. To obtain and maintain the small emittances imposes tight tolerances on spurious dispersion and orbit quality and stability. These limits will be given and discussed.  
 
THPKF028 Upgrade of the Cryomodule Prototype before its Implementation in SOLEIL dipole, storage-ring, impedance, synchrotron 2329
 
  • P. Bosland
    CEA/DSM, Gif-sur-Yvette
  • P. Bredy, S. Chel, G. Devanz
    CEA/DSM/DAPNIA, Gif-sur-Yvette
  • R. Losito
    CERN, Geneva
  • P. Marchand, K. Tavakoli, C. Thomas-Madec
    SOLEIL, Gif-sur-Yvette
  In the Storage Ring (SR) of the Synchrotron SOLEIL light source, two cryomodules will provide the maximum power of 600 kW required at the nominal energy of 2.75 GeV with the full beam current of 500 mA. A cryomodule prototype, housing two 352 MHz superconducting single-cell cavities with strong damping of the Higher Order Modes has been built and successfully tested in the ESRF storage ring. Even though the achieved performance (3 MV and 380 kW) does meet the SOLEIL requirement for the 1st year of operation, the cryomodule prototype will be upgraded before its installation in the SR early 2005. Modifications will be made on the internal cryogenic system, and also on the power and dipolar HOM couplers. That requires a complete disassembling and reassembling of the cryomodule, which is being carried out at CERN in the framework of collaboration between SOLEIL, CEA and CERN. Additional 3D RF calculations have been performed on the full SOLEIL RF structure in order to get a more detailed description of the dipolar modes damping and of the dipolar HOM couplers tuning. A second cryomodule, similar to the modified prototype, will be built and installed in the SR about one year later.  
 
THPKF036 Developments of the FZP Beam Profile Monitor alignment, coupling, radiation, background 2353
 
  • N. Nakamura, M. Fujisawa, H. Kudo, H. Sakai, K. Shinoe, H. Takaki, T. Tanaka
    ISSP/SRL, Chiba
  • H. Hayano, T. Muto
    KEK, Ibaraki
  A beam profile monitor based on two Fresnel Zone Plates (FZPs) has been developed at the KEK-ATF damping ring. This monitor can perform real-time imaging of the electron beam with an X-ray imaging optics and the synchrotron radiation and measure the horizontal and vertical beam sizes with a high spatial resolution. A clear electron-beam image with the vertical beam size less than 10 microns was already obtained in the early measurements [*]. Thereafter some of the optical elements, the crystal monochromator, X-ray CCD camera and FZP holders, were improved and an X-ray pinhole mask was installed between the two FZPs for reducing the background of X-rays passing through the MZP (the second FZP). Aberrations due to alignment errors of the FZPs were studied with an analytical approach and a ray-tracing method and vibrations of the optical elements were measured in order to estimate their effects on the system performance. In this paper, we will present developments of the beam profile monitor with results of some beam-size measurements.

* K. Iida et al., Nucl. Instrum. Methods A506, p.41-49 (2003); N. Nakamura et al., Proc. of PAC2003, p.530-532

 
 
THPLT016 LHC Orbit Feedback Tests at the SPS feedback, dipole, closed-orbit, alignment 2499
 
  • J. Wenninger, J. Andersson, L.K. Jensen, R.O. Jones, M. Lamont, R. Steinhagen
    CERN, Geneva
  The real-time orbit feedback system foreseen for the LHC will be an essential component for reliable and safe machine operation. A test setup including a number of beam position monitors equipped with the LHC acquisition and readout system have been installed in the SPS ring to perform prototyping work on such an orbit feedback. A closed loop digital feedback was implemented and tested with LHC beams on the SPS during the 2003 machine run. The feedback loop was tested successfully at up to 100 Hz. The performance of the feedback loop and of its constituents will be described.  
 
THPLT028 High Precision Cavity Beam Position Monitor dipole, resonance, background, coupling 2535
 
  • A. Liapine, H. Henke
    TET, Berlin
  A cavity beam position monitor is proposed for measuring the beam deflection in the TESLA energy spectrometer. The precision of the measurement has to be better than 1 micrometer. A slotted cavity is chosen as pick-up in order to reject the background signals and enhance the precision and the dynamic range of the monitor. The paper gives the design overview for two prototypes with operating frequencies of 1.5 GHz and 5.5 GHz, respectively. The results obtained on the test bench with direct conversion electronics are presented. A resolution of about 100 nm was achieved.  
 
THPLT043 Development of a New Orbit Measurement System storage-ring, controls, synchrotron, vacuum 2577
 
  • O. Kaul, F. Brinker, R. Neumann, R. Stadtmüller
    DESY, Hamburg
  Since DORIS III became a dedicated source for synchrotron radiation in 1993, the demands of the synchrotron-light-users concerning the beam position stability have permanently increased.In order to improve this stability, different measures have been adopted, all with success. The vacuum chambers have been renewed, since they were the source of quadrupole movement, which caused strong horizontal orbit distortion. In 2003 a new orbit position control was implemented, based on the ?Singular Value Decomposition? method. The position information comes from synchrotron light monitors, installed in the beam-lines, and from the orbit measurement system, which operates with a maximal measurement rate of 5Hz and a spatial resolution not less than 20μm. To satisfy the requirements for beam-position stability, the orbit measurement system has been further developed. The test stage is nearly finished and the new system will be installed soon. The orbit measurement rate will exceed 250Hz und the spatial resolution will be less than 2μm. In addition beam oscillations of up to 20Hz can be damped.  
 
THPLT056 Horizontal Instability and Feedback Performance in DAFNE e+ Ring feedback, pick-up, positron, injection 2613
 
  • A. Drago
    INFN/LNF, Frascati (Roma)
  In DAFNE, after the 2003 shutdown for the installation of FINUDA, a strong horizontal multibunch instability was found to limit the positron beam current at the level of ~450 mA. We have performed transverse grow-damp measurements in order to estimate the instability growth rates as well as the feedback damping rates for each bunch at different beam currents and to evaluate the tune shift along the bunch train. In particular, a strong dependence of oscillation amplitudes on the relative position of the bunch in the train has been observed. In this paper we describe the setup for multibunch oscillation amplitude recording, discuss the transverse feedback performance and summarize some observations on the transverse instability. The feedback rises the threshold by about a factor of two, depending on the machine configuration.  
 
THPLT068 Transverse Bunch-by-bunch Feedback System for the SPring-8 Storage Ring feedback, storage-ring, injection, emittance 2649
 
  • T. Nakamura, S. Daté, T. Ohshima
    JASRI/SPring-8, Hyogo
  • K. Kobayashi
    SES, Hyogo-pref.
  A transverse bunch-by-bunch feedback system is developed for the SPring-8 storage ring. An analog de-multiplexer is developed to slice out every six-bunch signal for high-resolution 12-bit ADCs of clock frequency 85MHz, one-sixth of 508MHz RF frequency. Six commercial ADC-FPGA-DAC boards are used for processing the signal from the de-multiplexer. A custom FPGA board is used to multiplex the output signals from those boards. The feedback system is installed in the ring and working with the damping time of 0.5~2.5ms in 30kHz-254MHz and can suppress multi-bunch instabilities driven by impedances of resistive-wall of in-vacuum insertion devices and cavity HOMs at low chromaticity operation.  
 
THPLT113 Conceptual Design of a Microwave Confocal Resonator Pick-up pick-up, coupling, impedance, extraction 2750
 
  • V.G. Ziemann, A. Ferrari, T. Lofnes
    TSL, Uppsala
  • F. Caspers, I. Syratchev
    CERN, Geneva
  A confocal resonator may be used as a pick-up for frequencies in the multi-GHz region. In this report we discuss the design by analytical and numerical methods of such a device. Furthermore we discuss engineering issues such as the damping of unwanted modes, shielding of image fields and manufacturing tolerances. Such a device can be used both as pick-up and kicker where the actual structure is several wavelengths away from the beam in the transverse direction. It is intended for highly relativistic beams and does not require changing particle trajectory as opposed to a diagnostic wiggler.  
 
THPLT123 Coupling Coefficients in the Inhomogeneous Cavity Chain coupling, electromagnetic-fields, acceleration 2759
 
  • K. Kramarenko, M.I. Ayzatskiy
    NSC/KIPT, Kharkov
  In this paper a mathematical method on the base of a rigorous electrodynamic approach for description of inhomogeneous chain of cylindrical cavities is presented. The form of the obtained for chosen amplitudes set of equations is similar to the set of equations that describe the simple coupled circuit chain. As the cavity have the infinite number of resonant frequencies, to obtain the coupling coefficients one have to solve additional infinite set of linear equations with coefficients that depend on the frequency. Using the developed method in the case of inhomogeneous cavity chain we calculated the dependence of the coupling coefficients on frequency and geometrical sizes with taking into account the 'long-range' coupling.  
 
THPLT155 Development and Testing of a Low Group-delay Woofer Channel for PEP-II feedback, impedance, diagnostics, synchrotron 2822
 
  • J.D. Fox, L. Beckman, D. Teytelman, D. Van Winkle, A. Young
    SLAC, Menlo Park, California
  The PEP-II HER and LER require active longitudinal feedback to control coupled-bunch instabilities. The PEP-II RF systems use direct and comb loop feedback to reduce the cavity fundamental impedance, though the remaining low-mode impedance is providing the fastest growing unstable modes in both rings. Since commissioning the longitudinal feedback systems have used a dedicated "woofer" channel to apply the low-frequency correction kick via the RF system. The performance of this original controller is limited by the maximum gain that can be supported due to the processing delay (group delay), as well as the difficulty in configuring a common correction controller that acts via two correction paths. A dedicated low-mode signal processing system has been developed to allow higher damping rates. It is a digital processing channel, operating at a 10 MHz sampling rate, and implementing flexible 5 to 10 tap FIR control filters. The design of the channel and initial control filters is presented, as are initial machine experiments quantifying the damping and noise floor of this low group delay woofer system.  
 
THPLT159 Instability Thresholds and Generation of the Electron-cloud in the GLC/NLC and Tesla Damping Rings electron, simulation, single-bunch, synchrotron 2831
 
  • M.T.F. Pivi, T.O. Raubenheimer
    SLAC/NLC, Menlo Park, California
  In the beam pipe of the Damping Ring (DR) of a linear collider, an electron cloud may be produced by ionization of residual gas and secondary emission. This electron cloud can reach equilibrium after the passage of only a few bunches. We present recent computer simulation results for the main features of the electron cloud generation in the GLC/NLC main DR and for the TESLA DR. Single and multi-bunch instability thresholds are also calculated for the NLC main DR. The results are obtained by the computer simulation codes HEAD-TAIL and POSINST, which were developed to study the electron cloud effect in particle accelerators.  
 
THPLT160 Measurements of Transverse Coupled-bunch Instabilities in PEP-II feedback, diagnostics, betatron, impedance 2834
 
  • D. Teytelman, R. Akre, J.D. Fox, S.A. Heifets, A. Krasnykh, D. Van Winkle, U. Wienands
    SLAC, Menlo Park, California
  At the design currents the PEP-II High and Low Energy Rings operate above the coupled-bunch instability thresholds in horizontal and vertical planes. Both machines have used analog bunch-by-bunch feedback systems to stabilize the beams since commissioning. Here we present a measurement technique that uses the capabilities of the PEP-II programmable digital longitudinal feedback system to provide transient diagnostics in X or Y directions. This technique allows one to measure instability growth or damping rates as well as oscillation frequencies in both open-loop and closed-loop conditions. Based on these measurements the configuration of the relevant transverse feedback channel can be optimized. The technique will be illustrated with instability measurements and feedback optimization examples. Comparisons of the measured modal patterns and growth rates to the theoretical predictions will be presented.  
 
FRXBCH02 Towards Higher Luminosities in B and Phi Factories luminosity, emittance, electron, background 286
 
  • P. Raimondi
    INFN/LNF, Frascati (Roma)
  A brief review of the performances of the existing Factories will be presented. Such machines have been proved extremely successful, for both particle and accelerator physics. To further extend their physics reach, several plans are under way to upgrade the existing colliders, in order to increase their luminosity up to an order of magnitude. Will also be described several new schemes and ideas to realize full ?Second Generation Factories? aimed at luminosities two order of magnitude higher then what achieved so far.  
Video of talk
Transparencies