Author: Salvant, B.
Paper Title Page
WEPPR062 The Mode Matching Method Applied to Beam Coupling Impedance Calculations of Finite Length Devices 3069
  • N. Biancacci, E. Métral, B. Salvant
    CERN, Geneva, Switzerland
  • M. Migliorati, L. Palumbo
    URLS, Rome, Italy
  • V.G. Vaccaro
    Naples University Federico II and INFN, Napoli, Italy
  The infinite length approximation is often used to simplify the calculation of the beam coupling impedance of accelerator elements. This is expected to be a reasonable assumption for devices whose length is greater than the transverse dimension but may be less accurate approximation for segmented devices. This contribution presents the study of the beam coupling impedance in the case of a finite length device: a cylindrical cavity loaded with a toroidal slab of material. In order to take into account the finite length we will decompose the field in the cavity and in the beam pipe into a set of orthonormal modes and apply the mode matching method to obtain the impedance. To validate our method, we will present comparisons between analytical formulas and 3D electromagnetic CST simulations as well as applications to the impedance of short beam pipe inserts, where the longitudinal and transverse dimensions are difficult to model in numerical simulations.  
WEPPR065 Electromagnetic Simulations of the Impedance of the LHC Injection Protection Collimator 3075
  • B. Salvant, V. Baglin, B. Goddard, A. Grudiev, E. Métral, M.A. Timmins
    CERN, Geneva, Switzerland
  During the 2011 LHC run, significant vacuum and temperature increase were observed at the location of the LHC injection protection collimators (TDI) during the physics fills. Besides, measurements of the LHC transverse tune shift while changing the TDI gap showed that the impedance of the TDI was significantly higher than the LHC impedance model prediction based on multilayer infinite length theory. This contribution details the electromagnetic simulations performed with a full 3D model of the TDI to obtain both longitudinal and transverse impedances and their comparison with measured observables.  
WEPPR070 Beam Coupling Impedance Simulations of the LHC TCTP Collimators 3090
  • H.A. Day, R.M. Jones
    UMAN, Manchester, United Kingdom
  • F. Caspers, A. Dallocchio, L. Gentini, A. Grudiev, E. Métral, B. Salvant
    CERN, Geneva, Switzerland
  As part of an upgrade to the LHC collimation system, 8 TCTP and 1 TCSG collimators are proposed to replace existing collimators in the collimation system. In an effort to review all equipment placed in the accelerator complex for potential side effects due to collective effects and beam-equipment interactions, beam coupling impedance simulations are carried out in both the time-domain and frequency-domain of the full TCTP design. Particular attention is paid to trapped modes that may induce beam instabilities and beam-induced heating due to cavity modes of the device.  
WEPPR071 Evaluation of the Beam Coupling Impedance of New Beam Screen Designs for the LHC Injection Kicker Magnets 3093
  • H.A. Day, R.M. Jones
    UMAN, Manchester, United Kingdom
  • M.J. Barnes, F. Caspers, H.A. Day, E. Métral, B. Salvant
    CERN, Geneva, Switzerland
  During the 2011 run of the LHC there was a measured temperature increase in the LHC Injection Kicker Magnets (LHC-MKI) during operation with 50ns bunch spacing. This was suspected to be due to increased beam-induced heating of the magnet due to beam impedance. Due to concerns about future heating with the increased total intensity to nominal and ultimate luminosities a review of the impedance reduction techniques within the magnet was required. A number of new beam screen designs are proposed and their impedance evaluated. Heating estimates are also given with a particular attention paid to future intensity upgrades to ultimate and HL-LHC parameters.  
WEPPR072 Increasing Instability Thresholds in the SPS by Lowering Transition Energy 3096
  • H. Bartosik, G. Arduini, T. Argyropoulos, T. Bohl, S. Cettour-Cave, K. Cornelis, J. Esteban Muller, W. Höfle, Y. Papaphilippou, G. Rumolo, B. Salvant, E.N. Shaposhnikova
    CERN, Geneva, Switzerland
  A new optics for the SPS with lower transition energy was tested experimentally during 2010-2011, showing a significant increase of the single bunch instability thresholds at injection, due to the 3-fold increase of the slip factor. This paper summarizes the series of performed machine studies for different LHC bunch structures and intensities. In particular, the search of the TMCI threshold in the new optics is presented. Observations on the longitudinal multi-bunch stability are compared between the nominal and the low-transition optics. Finally, optics variants with higher vertical tunes are discussed, which can allow to further increase the TMCI and vertical instability thresholds by reducing the vertical beta function.