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Impact of the 50 Hz harmonics on the beam evolution of the Large Hadron Collider

S. Kostoglou, G. Arduini, Y. Papaphilippou, G. Sterbini, and L. Intelisano
Phys. Rev. Accel. Beams 24, 034002 – Published 8 March 2021
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  • INTRODUCTION
  • LINEAR FORMALISM FOR A MODULATED DIPOLAR…
  • SIMULATIONS OF 50 Hz HARMONICS WITH…
  • SIMULATION BENCHMARK WITH CONTROLLED…
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
  • APPENDICES
    • References

    Abstract

    Harmonics of the mains frequency (50 Hz) have been systematically observed in the transverse beam spectrum of the Large Hadron Collider (LHC) since the start of its operation in the form of dipolar excitations. In the presence of strong nonlinearities such as beam-beam interactions, as many of these 50 Hz harmonics reside in the vicinity of the betatron tune they can increase the tune diffusion of the particles in the distribution, leading to proton losses and eventually to a significant reduction of the beam lifetime. The aim of this paper is to determine whether the 50 Hz harmonics have an impact on the beam performance of the LHC. A quantitative characterization of the 50 Hz ripple spectrum present in the operation of the accelerator, together with an understanding of its source is an essential ingredient to also evaluate the impact of the 50 Hz harmonics on the future upgrade of the LHC, the High Luminosity LHC (HL-LHC). To this end, simulations with the single-particle tracking code, sixtrack, are employed including a realistic 50 Hz ripple spectrum as extracted from experimental observations to quantify the impact of such effects in terms of tune diffusion, dynamic aperture, and beam lifetime. The methods and results of the tracking studies are reported and discussed in this paper.

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    • Received 8 September 2020
    • Accepted 18 February 2021

    DOI:https://doi.org/10.1103/PhysRevAccelBeams.24.034002

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Beam code development & simulation techniquesBeam lossSingle-particle dynamics
    Accelerators & Beams

    Authors & Affiliations

    S. Kostoglou*

    • CERN, Geneva 1211, Switzerland and National Technical University of Athens, Athens 15780, Greece

    G. Arduini, Y. Papaphilippou, and G. Sterbini

    • CERN, Geneva 1211, Switzerland

    L. Intelisano

    • CERN, Geneva 1211, Switzerland and INFN, Sapienza Università di Roma, Rome 00185, Italy

    • *sofia.kostoglou@cern.ch

    See Also

    Origin of the 50 Hz harmonics in the transverse beam spectrum of the Large Hadron Collider

    S. Kostoglou, G. Arduini, Y. Papaphilippou, G. Sterbini, and L. Intelisano
    Phys. Rev. Accel. Beams 24, 034001 (2021)

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    Vol. 24, Iss. 3 — March 2021

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    Images

    • Figure 1
      Figure 1

      The 50 Hz harmonics as a function of the horizontal amplitude in the Q7 pickup normalised to the beam size, as computed from the deflection and Eq. (8). A color code is assigned to the reduction of the minimum DA from the value computed in the absence of power supply ripple.

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    • Figure 2
      Figure 2

      The spectrum centered around the low (left) and high (right) frequency cluster as acquired experimentally from the horizontal plane of Beam 1 (black) and from tracking simulations (green).

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    • Figure 3
      Figure 3

      The frequency maps (left) and the initial configuration space (right) color-coded with the logarithm of the tune diffusion rate (Eq. (11) for the LHC simulation parameters of Table 2 (a) in the absence of power supply ripple, (b) with the 50 Hz harmonics of the low and (c) high-frequency cluster and (d) combining both regimes. The gray lines represent the nominal resonances and the green and purple lines illustrate the resonances [Eq. (12) and (13)] excited due to power supply ripple.

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    • Figure 4
      Figure 4

      Intensity evolution without power supply ripple (black), considering only the low (blue) or high (orange) frequency cluster and including the 50 Hz harmonics in both regimes (red).

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    • Figure 5
      Figure 5

      Intensity evolution in the absence of power supply ripple (black), including the power supply ripple spectrum of Beam 1 (blue) and 2 (red). The green line indicates the fits of the exponential decay of the intensity to compute lifetime (Eq. (16).

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    • Figure 6
      Figure 6

      The horizontal spectrum of a single bunch (black) during a controlled dipolar excitation at 2.5 kHz (green marker) performed using the transverse damper. The vertical lines represent the multiples of 50 Hz.

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    • Figure 7
      Figure 7

      The frequency of the excitation as a function of the deflection. A color code is assigned to the minimum DA computed with tracking simulations including power supply ripple. The star-shaped markers present the equivalent kicks, as computed from the beam spectrum and Eq. (8) during the controlled excitations with the transverse damper. The red markers indicate that the excitation had an impact on the beam lifetime. The blue markers denote the excitations that did not affect the beam lifetime.

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    • Figure 8
      Figure 8

      The horizontal amplitude as a function of the dipolar excitation frequency with θp=1  nrad as computed from the closed form of Eq. (8) (black) and from simulations (blue).

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