Abstract
Electrons lenses produce a high-intensity electron beam and have a variety of applications to circular hadron accelerators. Electron beams of different transverse cross sections and distributions may be designed, depending on the desired application, and they are produced and steered along the orbit of the hadron beam, overlapping with it for typical distances of a few meters before being deflected away and disposed of. Hollow electron beams find applications to high-intensity beam collimation for machines like the CERN Large Hadron Collider (LHC). Such devices can be integrated in a collimation system to improve the halo-cleaning performance through an active control of the halo dynamics: the annular distribution of the electrons excites resonantly the beam tails surrounding the beam core, while the core itself remains unperturbed, as ideally it only “sees” the field-free “hole” in the electron distribution. Hollow electron lenses are part of the upgrade baseline of the High-Luminosity project of the LHC (HL-LHC) and will be installed in the machine during a long shutdown in 2025–2027 to mitigate effects from beam losses so to improve the collimation system performance. This paper describes the hollow electron lens project within the HL-LHC collimation upgrade.
Highlights
: Electrons lenses produce a high-intensity electron beam and have a variety of applications to circular hadron accelerators
This paper describes the hollow electron lens project within the HL-Large Hadron Collider (LHC) collimation upgrade
Some additional factors must be taken into account to refine the possible operational scenarios that have been defined for the use of Hollow Electron Lens (HEL) in High-Luminosity project of the LHC (HL-LHC), such as pulse-to-pulse stability of the electron beam, linear coupling, and dependence on the betatron tune, which goes beyond the scope of this paper and can be found in [40]
Summary
The layout of the LHC ring is shown in figure 1. The two counter-rotating LHC beams are injected in Pt2 (Beam 1, clockwise) and Pt8 (Beam 2, counter-clockwise) This layout will be preserved for the HL-LHC, with major upgrades taking place in Pt1 and Pt5 in order to enable improved luminosity performance for the two generalpurpose experiments, ATLAS and CMS. We will see that the kick experienced by a halo particle at each passage through the HEL is of the order of a fraction of a microradian. Blue boxes indicate the “dogleg” dipoles that are used to increase the inter-beam distance in the straight region over a length of ≈ 100 m around Pt4 (s = 9997.1 m), as required for the LHC RF system [1]
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