Conceptual Design of the HL-LHC Hollow Electron Lens Superconducting Magnet System

The Hollow Electron Lens (HEL) units are part of the upgrade baseline of the High-Luminosity LHC accelerator (HL-LHC) and will be installed in the machine ring at point P4 on each counter-rotating LHC proton beamline during a long shutdown in 2025-2027 at CERN. The main goal is to improve the collimation system performance by controlling beam energy loss in the beam halo. The magnet system consists of two 1.6 m long, 5 T superconducting solenoids operating at constant current equipped with steering dipole correctors and fringe field coils which compress the annular low energy e-beam (15 keV) generated from the e
⁻
gun cathode and provide a stable interaction region with the high energy proton beam (7 TeV). Other sets of superconducting solenoids up to 4 T are used for fine-tuning and guiding the electron beam at the extremities of the interaction region on both the gun and the collector side. A standalone dipole compensator is part of the system to correct the net transverse field components up to 0.5 T.m. In this paper, the design progress of the HEL magnet system is presented and discussed.