- Open Access
Electron cloud energy distribution measurement and model in the LHC with the Vacuum Pilot Sector
Phys. Rev. Accel. Beams 29, 103502 – Published 15 October, 2026
DOI: https://doi.org/10.1103/fbwj-r3gx
Abstract
Electron cloud effects constitute a major performance limitation in high-intensity particle accelerators such as the Large Hadron Collider (LHC). A key ingredient for understanding and modeling these effects is the energy distribution of electrons impinging on the vacuum chamber walls. In this paper, we present direct measurements of electron cloud energy distributions obtained in the LHC Vacuum Pilot Sector (VPS) using retarding field analyzers with a beam pipe diameter of 8 cm, i.e., twice the LHC arc one. The VPS provides a dedicated, fully instrumented test environment for electron cloud studies under real LHC beam conditions. The measured energy spectra systematically exhibit a low-energy component associated with secondary electron emission and a higher-energy component originating from bunch-driven acceleration. To characterize these features, a phenomenological model is developed to reproduce the observed distributions up to 3 keV. Model parameters are extracted from a large dataset of LHC fills, with a representative 2025 physics fill used for detailed illustration. The evolution of the accelerated-electron peak is analyzed throughout the fill cycle and compared with predictions from the analytical kick approximation model. Good agreement is observed—particularly during the stable beam phase in one beamline—confirming that bunch-induced kicks dominate the electron energy gain in the field-free regions, as for the VPS. Discontinuities in the peak energy at operational transitions, as well as the recurrent observation of narrow accelerated peaks in the other beamline, are reported and suggest a dependence of the beam optics on the resulting energy gain. Finally, cumulative energy distribution functions are derived to quantify the fraction of electrons exceeding given energy thresholds. These results establish a quantitative experimental reference for energy-resolved electron cloud modeling in the LHC, providing direct inputs for electron cloud simulation benchmarking, heat load estimates, ESD modeling, and residual electron background assessment in ion diagnostics.
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