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Salvant, B.

Paper Title Page
TUPD049 Transverse Mode Coupling Instability Measurements at Transition Crossing in the CERN PS 2036
 
  • S. Aumon
    EPFL, Lausanne
  • S. Aumon, M. Delrieux, P. Freyermuth, S.S. Gilardoni, E. Métral, G. Rumolo, B. Salvant, R.R. Steerenberg
    CERN, Geneva
 
 

Transition crossing in the CERN PS is critical for the stability of high intensity beams, even with the use of a second order gamma jump scheme. The intense single bunch beam used for the neutron Time-of-Flight facility (n-ToF) needs a controlled longitudinal emittance blowup at flat bottom to prevent a fast single-bunch vertical instability from developing near transition. This instability is believed to be of Transverse Mode Coupling (TMCI) type. A series of measurements taken throughout 2008 and 2009 aim at using this TMCI observed on the ToF beam at transition, as a tool for estimating the transverse global impedance of the PS. For this purpose, we compare the measurement results with the predictions of the HEADTAIL code and find the matching parameters. This procedure also allows a better understanding of the different mechanisms involved and can suggest how to improve the gamma jump scheme for a possible intensity upgrade of the n-ToF beam.

 
TUPD055 Quadrupolar Transverse Impedance of Simple Models of Kickers 2054
 
  • B. Salvant
    EPFL, Lausanne
  • N. Mounet, E. Métral, G. Rumolo, B. Salvant, C. Zannini
    CERN, Geneva
 
 

The SPS kickers are major contributors to the SPS transverse beam coupling impedance. The current "flat chamber" impedance model for a kicker is obtained by applying form factors to the theoretical impedance of an axisymmetric ferrite beam pipe. This model was believed to be acceptable for the vertical dipolar impedance, as two-wire measurements on SPS kickers revealed a satisfactory agreement. However, one-wire measurements on PS kickers suggested that this model underestimates the kickers' transverse quadrupolar (detuning) impedance. The longitudinal and transverse dipolar impedances of another kicker model that accounts for the metallic plates on each side of the ferrite were derived in the past by H. Tsutsui. The same formalism is used in this paper to derive the quadrupolar impedance. These formulae were then successfully benchmarked to electromagnetic simulations. Finally, simulating the interaction of an SPS bunch with the improved kickers' model results in a positive horizontal tune shift, which is very close to the tune shift measured with the SPS beam.

 
TUPD056 Update of the SPS Impedance Model 2057
 
  • B. Salvant
    EPFL, Lausanne
  • G. Arduini, O.E. Berrig, F. Caspers, A. Grudiev, N. Mounet, E. Métral, G. Rumolo, B. Salvant, E.N. Shaposhnikova, C. Zannini
    CERN, Geneva
  • M. Migliorati, B. Spataro
    INFN/LNF, Frascati (Roma)
  • B. Zotter
    Honorary CERN Staff Member, Grand-Saconnex
 
 

The beam coupling impedance of the CERN SPS is expected to be one of the limitations to an intensity upgrade of the LHC complex. In order to be able to reduce the SPS impedance, its main contributors need to be identified. An impedance model for the SPS has been gathered from theoretical calculations, electromagnetic simulations and bench measurements of single SPS elements. The current model accounts for the longitudinal and transverse impedance of the kickers, the horizontal and vertical electrostatic beam position monitors, the RF cavities and the 6.7 km beam pipe. In order to assess the validity of this model, macroparticle simulations of a bunch interacting with this updated SPS impedance model are compared to measurements performed with the SPS beam.

 
WEPEB054 Analysis of the Performance of the SPS Exponential Coupler Striplines using Beam Measurements and Simulation Data 2812
 
  • R. De Maria
    BNL, Upton, Long Island, New York
  • C. Boccard, W. Höfle, G. Kotzian, C. Palau Montava, B. Salvant
    CERN, Geneva
 
 

The SPS exponential coupler stripline are used to study single bunch instabilities. An accurate description of the response of the pickup is required to obtain high resolution measurements of the bunch vertical motion along the longitudinal axis. In this study we present the results of the comparison between dedicated beam experiments and electromagnetic simulations of a geometrical model of the stripline.

 
TUOAMH01 First Cleaning with LHC Collimators 1237
 
  • D. Wollmann, O. Aberle, G. Arnau-Izquierdo, R.W. Assmann, J.-P. Bacher, V. Baglin, G. Bellodi, A. Bertarelli, A.P. Bouzoud, C. Bracco, R. Bruce, M. Brugger, S. Calatroni, F. Caspers, F. Cerutti, R. Chamizo, A. Cherif, E. Chiaveri, P. Chiggiato, A. Dallocchio, R. De Morais Amaral, B. Dehning, M. Donze, A. Ferrari, R. Folch, P. Francon, P. Gander, J.-M. Geisser, A. Grudiev, E.B. Holzer, D. Jacquet, J.B. Jeanneret, J.M. Jimenez, M. Jonker, J.M. Jowett, Y. Kadi, K. Kershaw, L. Lari, J. Lendaro, F. Loprete, R. Losito, M. Magistris, M. Malabaila, A. Marsili, A. Masi, S.J. Mathot, M. Mayer, C.C. Mitifiot, N. Mounet, E. Métral, A. Nordt, R. Perret, S. Perrollaz, C. Rathjen, S. Redaelli, G. Robert-Demolaize, S. Roesler, A. Rossi, B. Salvant, M. Santana-Leitner, I. Sexton, P. Sievers, T. Tardy, M.A. Timmins, E. Tsoulou, E. Veyrunes, H. Vincke, V. Vlachoudis, V. Vuillemin, Th. Weiler, F. Zimmermann
    CERN, Geneva
  • I. Baishev, I.A. Kurochkin
    IHEP Protvino, Protvino, Moscow Region
  • D. Kaltchev
    TRIUMF, Vancouver
 
 

The LHC has two dedicated cleaning insertions: IR3 for momentum cleaning and IR7 for betatron cleaning. The collimation system has been specified and built with tight mechanical tolerances (e.g. jaw flatness ~ 40 μm) and is designed to achieve a high accuracy and reproducibility of the jaw positions. The practically achievable cleaning efficiency of the present Phase-I system depends on the precision of the jaw centering around the beam, the accuracy of the gap size and the jaw parallelism against the beam. The reproducibility and stability of the system is important to avoid the frequent repetition of beam based alignment which is currently a lengthy procedure. Within this paper we describe the method used for the beam based alignment of the LHC collimation system, its achieved accuracy and stability and its performance at 450GeV.

 

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Slides

 
TUPEA076 Electron Cloud Measurements of Coated and Uncoated Vacuum Chambers in the CERN SPS by Means of the Microwave Transmission Method 1497
 
  • F. Caspers, S. Federmann, E. Mahner, P.C. Pinto, D. Seebacher, M. Taborelli
    CERN, Geneva
  • B. Salvant
    EPFL, Lausanne
  • C. Yin Vallgren
    Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg
 
 

Electron cloud is a limitation to increasing the beam current in the CERN SPS in the frame of an intensity upgrade of the LHC complex. Coating the vacuum chamber with a thin amorphous carbon layer is expected to reduce the electron cloud build-up. Three SPS straight sections have been coated to study the performance of this carbon coating. The microwave transmission method is one possible way to monitor electron cloud and hence to test the effect of the coating. In this paper the evolution of the experimental setup for measurements of the electron cloud using LHC type beams with different bunch spacing will be described. Due to the low revolution frequency of about 43 kHz serious electromagnetic compatibility problems and intermodulation have been found. These effects and their mitigation are described. Finally we present the measurement results illustrating the possible reduction due to the carbon coating.

 
TUPD052 Electromagnetic Simulations of Simple Models of Ferrite Loaded Kickers 2045
 
  • C. Zannini, N. Mounet, E. Métral, G. Rumolo
    CERN, Geneva
  • B. Salvant, C. Zannini
    EPFL, Lausanne
 
 

The kickers are major contributors to the CERN SPS beam coupling impedance. As such, they may represent a limitation to increasing the SPS bunch current in the frame of an intensity upgrade of the LHC. In this paper, CST Particle Studio time domain electromagnetic simulations are performed to obtain the longitudinal and transverse impedances/wake potentials of simplified models of ferrite loaded kickers. The simulation results have been successfully compared with some existing analytical expressions. In the transverse plane, the dipolar and quadrupolar contributions to the wake potentials have been estimated from the results of these simulations. For some cases, simulations have also been benchmarked against measurements on PS kickers. It turns out that the large simulated quadrupolar contributions of these kickers could explain both the negative total (dipolar+quadrupolar) horizontal impedance observed in bench measurements and the positive horizontal tune shift measured with the SPS beam.

 
TUPD055 Quadrupolar Transverse Impedance of Simple Models of Kickers 2054
 
  • B. Salvant
    EPFL, Lausanne
  • N. Mounet, E. Métral, G. Rumolo, B. Salvant, C. Zannini
    CERN, Geneva
 
 

The SPS kickers are major contributors to the SPS transverse beam coupling impedance. The current "flat chamber" impedance model for a kicker is obtained by applying form factors to the theoretical impedance of an axisymmetric ferrite beam pipe. This model was believed to be acceptable for the vertical dipolar impedance, as two-wire measurements on SPS kickers revealed a satisfactory agreement. However, one-wire measurements on PS kickers suggested that this model underestimates the kickers' transverse quadrupolar (detuning) impedance. The longitudinal and transverse dipolar impedances of another kicker model that accounts for the metallic plates on each side of the ferrite were derived in the past by H. Tsutsui. The same formalism is used in this paper to derive the quadrupolar impedance. These formulae were then successfully benchmarked to electromagnetic simulations. Finally, simulating the interaction of an SPS bunch with the improved kickers' model results in a positive horizontal tune shift, which is very close to the tune shift measured with the SPS beam.

 
TUPD056 Update of the SPS Impedance Model 2057
 
  • B. Salvant
    EPFL, Lausanne
  • G. Arduini, O.E. Berrig, F. Caspers, A. Grudiev, N. Mounet, E. Métral, G. Rumolo, B. Salvant, E.N. Shaposhnikova, C. Zannini
    CERN, Geneva
  • M. Migliorati, B. Spataro
    INFN/LNF, Frascati (Roma)
  • B. Zotter
    Honorary CERN Staff Member, Grand-Saconnex
 
 

The beam coupling impedance of the CERN SPS is expected to be one of the limitations to an intensity upgrade of the LHC complex. In order to be able to reduce the SPS impedance, its main contributors need to be identified. An impedance model for the SPS has been gathered from theoretical calculations, electromagnetic simulations and bench measurements of single SPS elements. The current model accounts for the longitudinal and transverse impedance of the kickers, the horizontal and vertical electrostatic beam position monitors, the RF cavities and the 6.7 km beam pipe. In order to assess the validity of this model, macroparticle simulations of a bunch interacting with this updated SPS impedance model are compared to measurements performed with the SPS beam.