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In situ estimation of the maximum secondary electron yield in the LHC Vacuum Pilot Sector beam pipe via electron cloud measurements and numerical simulations

Quentin Duong1,*, Vincent Baglin1, and Gaël Sattonnay2

  • *PHENIICS Doctoral School, Paris-Saclay University, 91405 Orsay, France.
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Phys. Rev. Accel. Beams 29, 083503 – Published 31 August, 2026

DOI: https://doi.org/10.1103/6hvz-l89v

Abstract

The maximum secondary electron yield, δmax, is a key parameter governing electron cloud buildup in high-intensity proton accelerators, yet its direct in situ determination under operational conditions remains challenging. This paper presents a novel method to estimate δmax in the Large Hadron Collider (LHC) using electron cloud measurements performed in the Vacuum Pilot Sector. The approach exploits the characteristic evolution of electron cloud intensity during beam injection, in particular the transition from an initial build-up regime to a linear scaling of electron flux with the number of injected bunches. Electron cloud currents measured with dedicated electron pickups are compared with PyECLOUD simulations performed for varying δmax values. The threshold number of injected bunches required to reach the linear regime provides a robust observable from which δmax can be extracted with limited sensitivity to other surface-emission parameters. The method is applied to multiple LHC fills and surface materials. For conditioned copper liners, δmax values between approximately 1.16 and 1.30 are obtained, in agreement with independent analyses and literature values. Applying the technique over extended operation periods enables the reconstruction of surface conditioning curves as a function of cumulative electron dose. These curves show a rapid initial decrease in δmax before approaching an apparent plateau, which may lie below the detection limit of the method depending on the beam pipe material and location. The method is compatible with routine LHC operation and enables systematic monitoring of vacuum-surface conditioning.

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Phys. Rev. Accel. Beams 29, 083503– Published 31 August, 2026
  • Received 17 April 2026
  • Accepted 27 July 2026
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