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single-bunch

 
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MOPCH160 A Beam-based High Resolution Phase Imbalance Measurement Method for the ILC Crab Cavities dipole, positron, linear-collider, electron 433
 
  • A. Kalinin, L. Ma, R.J. Smith
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  A high resolution method of RF phase adjustment and test is proposed for the Crab Cavity system of the ILC. The method is based on beam as ultimate test instrument. To measure phase imbalance in the pair of crab cavities (<0.02deg at 1.3GHz is required), a low energy (~1GeV) beam is used. A bunch center-of-mass trajectory through the cavities spaced (n+1/2) RF wavelengths and excited as in the case of the ILC, is a straight line for phase-balanced cavities and gets a kick when unbalanced. The kick is measured by two spaced BPMs with reference to the initial trajectory angle measured by two other BPMs. The method is insensitive to a bunch arrival time jitter and RF phase Common Mode jitter. A prototype of the test bench based on the method, is proposed. Using a 10MeV beam, two simple dipole cavities and low RF power, the prototype can be utilized for mastering high resolution measurements, for adjustment and tests of low level electronics of the Crab Cavity system and RF systems of XFEL ERLs as well. The phase resolution of the prototype is estimated as 0.01deg and the amplitude resolution as 0.01%.  
 
MOPLS108 Liquid Metal Target for ILC target, positron, undulator, electron 816
 
  • A.A. Mikhailichenko
    Cornell University, Department of Physics, Ithaca, New York
  We considered the Hg target for gamma/positron conversion suitable for usage in ILC project. Positron scheme generation with undulator allows usage thin Hg jet confined in profiled duct with rectangular cross-section.  
 
TUPCH106 Commissioning the SPEAR3 Diagnostic Beamlines diagnostics, optics, coupling, photon 1259
 
  • W.J. Corbett, C. Limborg-Deprey, W.Y. Mok, A. Ringwall
    SLAC, Menlo Park, California
  SPEAR 3 has two diagnostic beam lines: an x-ray pinhole camera and a visible/UV laboratory. The pinhole camera images ~8 keV dipole radiation on a phosphor screen with a remote computer to capture digital profile images. The visible/UV beam line features an 8 mm high GlidCop 'cold finger' to remove the x-ray core of the beam. The remaining light is deflected horizontally onto an optical bench where it is focused via reflective (Cassegrain) or refractive optics. The visible beam is then split into branch lines for a variety of experimental applications. This paper describes the experimental arrangement, data processing algorithms and measurements obtained with both systems.  
 
TUPCH109 Ion-related Phenomenon in UVSOR/UVSOR-II Electron Storage Ring ion, vacuum, electron, storage-ring 1265
 
  • A. Mochihashi, K. Hayashi, M. Hosaka, M. Katoh, J. Yamazaki
    UVSOR, Okazaki
  • Y. Hori
    KEK, Ibaraki
  • Y. Takashima
    Nagoya University, Nagoya
  A vertical betatron tune shift depending on beam current under multibunch condition was observed in the UVSOR storage ring. Vertical tune increased as beam current decreased, and the slope of the tune shift depended on the condition of the vacuum in the ring. Such a change in vertical tune was explained by a change in the stability condition of trapped ions*/** with the beam current. Based on a theoretical model*** that gives density of the trapped ions the experimental results were discussed via analytic and tracking calculations. Both the effect from the residual gas ions generated by scattering between high energy electrons and molecules and that from dissociated ions that come from secondary ionization processes have been discussed. In quest of the ion-related phenomenon in single-bunch condition, precise tune measurement has been also performed in the UVSOR-II storage ring. The experimental results in the single-bunch condition have been discussed. Precise measurement of vacuum pressure in the beam duct is a key issue of the ion-related phenomenon. A design of vacuum pressure measurement system via detecting residual gas fluorescence will be introduced in the presentation.

*R. D. Kohaupt. DESY Internal. Bericht No.H1-71/2 (1971). **Y. Baconnier and G. Brianti. CERN Internal Report No.CERN/SPS/80-2(DI) (1980). ***A. Mochihashi et al. Jpn. J. Appl. Phys. 44 (2005) 430.

 
 
WEOFI02 RF Phase Modulation Studies at the LNLS Electron Storage Ring damping, synchrotron, electron, storage-ring 1905
 
  • N.P. Abreu, R.H.A. Farias, P.F. Tavares
    LNLS, Campinas
  In this work we present a set of measurements of the effectiveness of RF phase modulation on the second harmonic of the RF frequency as a mechanism to damp longitudinal coupled-bunch instabilities. We also propose a theoretical model of the damping mechanism, in which the increase of the spread in synchrotron frequencies inside the bunches produced by phase modulation is responsible for damping the centroid dipolar coherent motion caused by an external excitation, which could be a Higher Order Mode (HOM) of the RF cavities driving the coupled bunch motion. We measured the coherent synchrotron oscillation damping of a single bunch under two circumstances, with and without phase modulation, and determined the amount of extra damping due to the modulation. With this experiment we could also measure the frequency of small oscillations around the stable islands formed by phase modulation and its behavior when the RF phase modulation amplitude and frequency are changed. We performed measurements of Beam Transfer Function (BTF) to observe the effects of phase modulation over the stable area for coherent oscillations and compared the results with a theoretical model.  
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WEPCH078 Measurement of Wake Effects by Means of Tune Shift in the KEKB Low-Energy Ring electron, positron, betatron, KEKB 2101
 
  • T. Ieiri, H. Fukuma, Y. Ohnishi, M. Tobiyama
    KEK, Ibaraki
  The electron cloud produced by the positron beam induces single-bunch and coupled-bunch wakes, in addition to a tune shift. Effects of the dipole wake-field including the electron cloud were tried to measure in the KEKB Low Energy Ring. A test bunch was placed behind a bunch-train of the positron beam, even though a test bunch itself might interact with the remaining electron cloud. We measured a current-dependent tune-shift of a test bunch under constant train-current, while changing the bucket position of a test bunch. The tune shift indicated a strong defocusing field, however, tended to a focusing field when a test bunch approached a train with high train-current. The results are discussed, considering variations of the electron cloud density.  
 
THPCH032 Instability Studies Using Evaluated Wake Fields and Comparison with Observations at SOLEIL impedance, SOLEIL, simulation, betatron 2847
 
  • R. Nagaoka
    SOLEIL, Gif-sur-Yvette
  Beam instability is predicted for SOLEIL using the impedance data obtained through component-wise numerical evaluations. The paper also attempts to make the first comparison with measurements. A key issue for SOLEIL has been to acquire precise knowledge of impedance up to a few tens of GHz, due to short bunches, of chambers which are essentially 3D and additionally NEG coated to a large part, which is expected to enhance the reactive part of the resistive-wall impedance. The predictability of instabilities with the data attained thus becomes a large concern. Wake potentials computed with a 3D code are transformed to impedances and decomposed into a series of resonators, inductive and resistive components, to deduce the wake functions, while for NEG coated chambers, they are numerically Fourier transformed from analytically derived impedances. Both time and frequency domain simulations are performed to predict the longitudinal and transverse instabilities in single bunch, as well as resistive-wall instabilities in multibunch as a function of chromaticity. A multibunch tracking is also performed to investigate the filling pattern dependence of the latter.  
 
THPCH033 Recent Studies of Geometric and Resistive-wall Impedance at SOLEIL impedance, SOLEIL, LEFT, vacuum 2850
 
  • R. Nagaoka, J.-C. Denard, M.-P. Level
    SOLEIL, Gif-sur-Yvette
  Coupling impedance studies are of great importance for SOLEIL not only to avoid beam instability, but also to ensure protection of a concerned chamber from EM fields excited by the beam. This paper deals with components that required particularly such efforts, which include BPMs, ceramic chambers, and a vertical scraper. The heat deposited in the BPM buttons is investigated as a function of the gap between a button and an electrode, button diameter and thickness. High temperatures on a vacuum tight feed-through would be a problem, affecting the measurement stability at high currents. Coupling of a trapped mode among successively passing bunches is also investigated. To evaluate the heat deposited in a titanium coated ceramic chamber, its impedance is analytically solved using the field matching technique. The solution obtained justifies the image current model that assumes a constant image current density across the coating when the skin depth is greater than the coating thickness. The azimuthal image current distribution is pursued with Piwinski's formalism for flat chambers. The paper also deals with components not treated earlier such as a stripline.  
 
THPCH035 Characterisation of the EU-HOM-damped Normal Conducting 500 MHz Cavity from the Beam Power Spectrum at DELTA CBM, impedance, synchrotron, storage-ring 2856
 
  • R.G. Heine, P. Hartmann, T. Weis
    DELTA, Dortmund
  A HOM-damped prototype cavity developed in the framework of an EC collaboration has been installed into the Dortmund synchrotron light source DELTA. This paper reports on beam studies performed at beam energies of 1.5 GeV and 542 MeV in an attempt to get information on coupled bunch instability thresholds. In addition an evaluation of the longitudinal cavity impedance is presented, based on beam power spectra up to 3 GHz for different filling patterns of the storage ring by analysing the RF signal from the HOM-dampers.  
 
THPCH167 Commissioning of the Diamond Pre-injector Linac linac, emittance, dipole, DIAMOND 3185
 
  • C. Christou, V.C. Kempson
    Diamond, Oxfordshire
  • K. Dunkel, C. Piel
    ACCEL, Bergisch Gladbach
  Commissioning of the linac for the Diamond Light Source (DLS) was completed in October 2005. The linac was supplied by Accel Instruments as a complete system, with DLS providing beam diagnostics, beam analysis software, control system hardware and standard vacuum components. Much of the beam analysis was carried out using the first part of the Linac to Booster transfer line (LTB), which was designed and built by DLS. Operation of the linac and LTB at 100 MeV in long-pulse and short-pulse modes of operation was demonstrated, and all operational parameters were measured to be within specification.  
 
THPLS012 Commissioning of the Australian Synchrotron Injector RF Systems booster, linac, controls, electron 3293
 
  • C. Piel, K. Dunkel, J. Manolitsas, D. Trompetter, H. Vogel
    ACCEL, Bergisch Gladbach
  • M.J. Boland, R.T. Dowd, G. LeBlanc, M.J. Spencer, Y.E. Tan
    ASP, Clayton, Victoria
  On December 16, 2003 the contract for the design, manufacture, installation and commissioning of the turnkey injector system for the Australian Synchrotron Project was awarded to industry. ACCEL Instruments is delivering the turnkey 100MeV linac and the booster RF system. Commissioning of the linac for ASP was performed in December 2005, right after successful commissioning of the Diamond Light Source injection linac*. The 500MHz booster cavity and related low level RF system will be commissioned after installation of the booster is finalised in early 2006. The paper will present design and layout information, as well as commissioning results.

*Commissioning of the Diamond Pre-Injector Linac (this conference).