Hollow electron lens (HEL)
Hollow electron lenses (HEL) are devices for active halo control, providing the means to scatter particles in the beam towards the LHC collimation where they can be disposed. For the envisaged HL-LHC beam intensities, active halo control will become a crucial incredient to protect the LHC hardware from sudden strong beam loss which might be caused due to orbit jitter or crab cavity failures.
Working principle
Hollow electron lenses are designed to produce an electron beam of annular shape which is moving in the opposite direction of the hadron beam in the collider. Particles at amplitudes large enough such that their trajectory overlaps with the area covered by the electron beam receive a transverse kick towards the primary collimator.
The system is designed to provide clearance between the particles in the beam core (which are contributing to the luminosity) and the LHC collimation system. This clearance (measured in units of the transverse beam size) provides a tolerance against orbit jitter without endangering the LHC collimators and the superconducting LHC magnets.
Updates and News
Hollow e-lenses are now part of the HL-HEL WP5 upgrade baseline!
09.02.2022:
Impact of phase shifts in pulsed operation of the HEL,
M. Boucard, Presentation at the 25th NDC Section Meeting
17.12.2021:
HEL residual kick compensation with the transverse damper,
P. Hermes et al., Presentation at the ColUSM Meeting 147
01.12.2021:
Beam tests with HEL at RHIC,
P. Hermes et al., Presentation at the 22nd NDC Section Meeting
13.04.2021:
HEL functional specification,
S. Redaelli et al., HL-LHC Hollow Electron Lens (production) kick-off meeting, 13th April 2021.
13.04.2021:
Hollow electron lens kick-off meeting
01.04.2020:
Status of SixTrack Implementation for Hollow Electron Lenses,
A. Mereghetti, E-Beam – #2 Remote WG Meeting.
30.01.2020:
Recent design updates new gun design
Relevant Publications
S. Redaelli, R.B. Appleby, R. Bruce, O. Brüning, A. Kolehmainen, G. Ferlin, A. Foussat, M. Giovannozzi, P. Hermes, D. Mirarchi, D. Perini, A. Rossi, G. Stancari, Hollow electron lenses for beam collimation at the High-Luminosity Large Hadron Collider (HL-LHC), Journal of Instrumentation, 16, 2021. Weblink.
D. Mirarchi, H. Garcia Morales, A. Mereghetti, S. Redaelli, W. Fischer, X. Gu, G. Stancari, Hollow electron-lens assisted collimation and plans for the LHC, Proceedings of the 61st ICFA Advanced Beam Dynamics Workshop on High-Intensity and High-Brightness Hadron Beams, Daejeon, Korea, 2018. Weblink. [BibTex reference key: osti_1463620]
Presentations and recent material
Nonlinear dynamics and depletion efficiency
D. Mirarchi et al., Nonlinear dynamics of proton beams with hollow electron lens in the CERN High-Luminosity LHC.
NLBD-WG Meeting, 25th March 2021.
Chebyshev polynomials
A. Mereghetti, Status of Simulations and Required Inputs,
122nd Collimation Upgrade Specification Meeting, ColUSM, 22nd November 2019.
External and internal project reviews on HEL for collimation
2017 review on "E-lens concept readiness for integration in the HL-LHC baseline"