Hollow electron lenses for beam collimation at the High-Luminosity Large Hadron Collider (HL-LHC)

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. K: Accelerator Applications; Accelerator modelling and simulations (multi-particle dynamics; single-particle dynamics); Accelerator Subsystems and Technologies; Beam dynamics Work supported by the HL-LHC project.

Nonlinear dynamics of proton beams with hollow electron lens in the CERN high-luminosity LHC

“…Scaling these observations to HL-LHC beams, under the assumption that their population scales linearly with the bunch intensity, led to the conclusion that up to about 36 MJ might be stored in the beam tails [16]. The beam parameters of our interest are reported in Table 1, while a complete overview can be found in [17,18]. Such a large amount of energy can cause unforeseen beam dumps, in case of orbit jitter, and fast-failure scenarios related for example to crab cavities (CC), due to the high beam losses that would take place on primary collimators [19,20].…”

“…Table 1 Nominal HL-LHC beam parameters with colliding beams and standard filling pattern [17,18], where σ is the transverse RMS beam size assuming a Gaussian proton beam distribution…”

Electron dynamics for high-intensity hollow electron beams

“…In fact, given a maximum magnetic field at the mains of 5 T, a maximum field at the cathode of 4 T, and cathode raddi equal to 4.02-8.05 mm, the largest electron beam size achievable in the interaction region will be of 3.6-7.2 mm, which is smaller than the LHC beam at injection energy ( 450). Operation of the HEL are discussed in more details in [1]. In the gap between the two main solenoids, the magnetic field inevitably decreases, with -4 -a minimum of ∼ 1.1 T at the gap centre.…”

Calculations of detuning with amplitude for the McMillan electron lens in the Fermilab Integrable Optics Test Accelerator (IOTA)

“…In particular, one straight section is designed to include an electron lens, which will be used for research on nonlinear dynamics, electron cooling, and space-charge compensation [7][8][9]. Because of their flexibility, electron lenses can be designed to have different effects on the circulating beam [10][11][12][13][14].…”