Author: Métral, E.
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MOP10 Closed Form Formulas of the Indirect Space Charge Wake Function for Axisymmetric Structures 65
 
  • N. Mounet, E. Dadiani, E. Métral, C. Zannini
    CERN, Geneva, Switzerland
  • A. Rahemtulla
    EPFL, Lausanne, Switzerland
 
  Indirect space charge contributes significantly to the impedance of non ultrarelativistic machines such as the LEIR, PSB and PS, at CERN. While general expressions exist in frequency domain for the beam coupling impedance, the time domain wake function is typically obtained numerically, thanks to an inverse Fourier transform. An analytical expression for the indirect space charge wake function, including the time dependence as a function of particle velocity, is nevertheless highly desirable to improve the accuracy of time domain beam dynamics simulations of coherent instabilities. In this work, a general formula for the indirect space charge wake function is derived from the residue theorem. Moreover, simple approximated expressions reproducing the time and velocity dependence are also provided, which can even be corrected to recover an exact formula, thanks to a numerical factor computed once for all. The expressions obtained are successfully benchmarked with a purely numerical approach based on the Fourier transform.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2021-MOP10  
About • Received ※ 30 September 2021 — Revised ※ 28 October 2021 — Accepted ※ 22 November 2021 — Issue date ※ 30 January 2022
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MOP12 Understanding of the CERN-SPS Horizontal Instability with Multiple Bunches 77
 
  • C. Zannini, H. Bartosik, M. Carlà, K.S.B. Li, E. Métral, G. Rumolo, B. Salvant
    CERN, Geneva, Switzerland
  • L.R. Carver
    ESRF, Grenoble, France
  • M. Schenk
    EPFL, Lausanne, Switzerland
 
  At the end of 2018, an instability with multiple bunches has been consistently observed during high intensity studies at the CERN-SPS. This instability could be a significant limitation to achieve the bunch intensity expected after the LHC Injector Upgrade (LIU). Therefore, a deep understanding of the phenomena is essential to identify the best mitigation strategy. Extensive simulation studies have been performed to explore the consistency of the current SPS model, give a possible interpretation of the instability mechanism and outline some possible cures.  
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DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2021-MOP12  
About • Received ※ 07 October 2021 — Revised ※ 20 October 2021 — Accepted ※ 28 December 2021 — Issue date ※ 11 April 2022
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TUAC3
Transverse Damper and Stability Diagram  
 
  • S.A. Antipov
    DESY, Hamburg, Germany
  • D. Amorim
    SOLEIL, Gif-sur-Yvette, France
  • N. Biancacci, X. Buffat, N. Mounet, E. Métral, D. Valuch
    CERN, Meyrin, Switzerland
  • A. Oeftiger
    GSI, Darmstadt, Germany
 
  Landau damping is an essential mechanism for ensuring collective beam stability in particle accelerators. Precise knowledge of the strength of Landau damping is key to making accurate predictions on beam stability for state-of-the-art high-energy colliders. We demonstrate an experimental procedure that would allow quantifying the strength of Landau damping and the limits of beam stability using an active transverse feedback as a controllable source of beam coupling impedance. In a proof-of-principle test performed at the Large Hadron Collider, stability diagrams for a range of Landau octupole strengths have been measured. In the future, the procedure could become an accurate way of measuring stability diagrams throughout the machine cycle.  
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FRPS1
Summary WG-A  
 
  • J.S. Eldred
    Fermilab, Batavia, Illinois, USA
  • W. Fischer
    BNL, Upton, New York, USA
  • E. Métral
    CERN, Meyrin, Switzerland
 
  Summary of the Working Group A (Beam Dynamics in Rings)  
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FRCLS1
Closeout & Announcement of HB2023  
 
  • I. Hofmann
    GSI, Darmstadt, Germany
  • E. Métral
    CERN, Meyrin, Switzerland
 
  Closing of HB2021 and Announcement of HB2023  
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