TUA —  WGA - Deam Dynamics in Rings   (05-Oct-21   10:00—11:00)
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TUAC1 Self-Consistent Long-Term Dynamics of Space Charge Driven Resonances in 2D and 3D 160
  • A. Oeftiger, I. Hofmann
    GSI, Darmstadt, Germany
  • O. Boine-Frankenheim
    TEMF, TU Darmstadt, Darmstadt, Germany
  Understanding the 3D collective long-term response of beams exposed to resonances is of theoretical interest and essential for advancing high intensity synchrotrons. This study of a hitherto unexplored beam dynamical regime is based on 2D and 3D self-consistent particle-in-cell simulations and on careful analysis using tune spectra and phase space. It shows that in Gaussian-like beams Landau damping suppresses all coherent parametric resonances, which are of higher than second order (the "envelope instability"). Our 3D results are obtained in an exemplary stopband, which includes the second order coherent parametric resonance and a fourth order structural resonance. They show that slow synchrotron oscillation plays a significant role. Moreover, for the early time evolution of emittance growth the interplay of incoherent and coherent resonance response matters, and differentiation between halo and different core regions is essential. In the long-term behavior we identify a progressive, self-consistent drift of particles toward and across the resonance, which results in effective compression of the initial tune spectrum. However, no visible imprint of the coherent features is left over, which only control the picture during the first one or two synchrotron periods. An intensity limit criterion and an asymptotic formula for long-term rms emittance growth are suggested. Comparison with the commonly used non-self-consistent "frozen space charge" model shows that in 3D this approximation yields a fast and useful orientation, but it is a conservative estimate of the tolerable intensity.
HB’21 talk on "Effect of Space Charge on Bunch Stability and Space Charge Compensation Schemes" based on this APS PR-AB published contribution.
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slides icon Slides TUAC1 [2.836 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2021-TUAC1  
About • Received ※ 11 October 2021 — Revised ※ 04 November 2021 — Accepted ※ 05 November 2021 — Issue date ※ 23 November 2021
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TUAC2 Impact of Power Supply Ripple on the Beam Performance of the Large Hadron Collider and the High-Luminosity LHC 170
  • S. Kostoglou, H. Bartosik, Y. Papaphilippou, G. Sterbini
    CERN, Geneva, Switzerland
  Harmonics of the mains frequency (50 Hz) have been systematically observed in the form of dipolar excitations in the transverse beam spectrum of the Large Hadron Collider (LHC) since the beginning of its operation. The power supply ripple, consisting of both fundamental and higher frequency components, is proven not to be the result of an artifact of the instrumentation systems with which they are observed. Potential sources of the perturbation have been identified through systematic analysis and experimental studies. Single-particle tracking simulations have been performed including a realistic power supply ripple spectrum, as acquired from experimental observations, to demonstrate the impact of such noise effects on beam performance.  
slides icon Slides TUAC2 [3.678 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-HB2021-TUAC2  
About • Received ※ 04 October 2021 — Revised ※ 20 October 2021 — Accepted ※ 23 November 2021 — Issue date ※ 25 February 2022
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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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