First Experience of Crystal Collimators During LHC Special Runs and Plans for the Future
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M. D’Andrea, V. Avati, R. Bruce, M.E.J. Butcher, M. Deile, M. Di Castro, H. García Morales, S. Jakobsen, J. Kašpar, I. Lamas Garcia, A. Masi, A. Mereghetti, D. Mirarchi, S. Redaelli, B. Salvachúa, P. Serrano Galvez, M. Solfaroli Camillocci
CERN, Geneva, Switzerland
Yu.A. Gavrikov
PNPI, Gatchina, Leningrad District, Russia
K.H. Hiller
DESY Zeuthen, Zeuthen, Germany
N. Turini
UNISI, Siena, Italy
Bent crystals can deflect charged particles by trapping them within the potential well generated by neighboring crystalline planes and forcing them to follow the curvature of the crystal itself. This property has been extensively studied over the past decade at the CERN accelerator complex, as well as in other laboratories, for a variety of applications, ranging from beam collimation to beam extraction and in-beam fixed target experiments. In 2018, crystal collimators were operationally used for the first time at the Large Hadron Collider (LHC) during a special high-beta* physics run with low-intensity proton beams, with the specific goal of reducing detector background and achieving faster beam halo removal. This paper describes the preparatory studies carried out by means of simulations, the main outcomes of the special physics run and plans for future uses of this innovative collimation scheme, including the deployment of crystal collimation for the High-Luminosity LHC upgrade.
P.D. Hermes, R. Bruce, R. De Maria, M. Giovannozzi, A. Mereghetti, D. Mirarchi, S. Redaelli
CERN, Geneva, Switzerland
G. Stancari
Fermilab, Batavia, Illinois, USA
Each of the two proton beams in the High-Luminosity Large Hadron Collider (HL-LHC) will carry a total energy of 720 MJ. One concern for machine protection is the energy stored in the transverse beam tails, estimated to potentially reach up to 5% of the total stored energy. Several failure scenarios could drive these tails into the collimators, potentially causing damage and therefore severely affecting operational efficiency. Hollow Electron Lenses (HEL) were integrated in the HL-LHC baseline to mitigate this risk by depleting the tails in a controlled way. A hollow-shaped electron beam runs co-axially to the hadron beam over about 3 m, such that halo particles at large amplitudes become unstable, while core particles ideally remain undisturbed. Residual fields from e-beam asymmetries can, however, induce emittance growth of the beam core. Various options for the pulsing of the HEL are considered and are compared using two figures of merit: halo depletion efficiency and core emittance growth. This contribution presents simulations for these two effects with different HEL pulsing modes using the final HL-LHC optics, that was optimized at the location of the lenses.
Status of Layout Studies for Fixed-Target Experiments in Alice Based on Crystal-Assisted Halo Splitting
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M. Patecki, D. Kikoła
Warsaw University of Technology, Warsaw, Poland
A.S. Fomin, D. Mirarchi, S. Redaelli
CERN, Geneva, Switzerland
Funding:This project has received funding from the European Union’s Horizon 2020 research and innovation programme. The Large Hadron Collider (LHC) at the European Organization for Nuclear Research (CERN) is the world largest and most powerful particle accelerator colliding beams of protons and lead ions at energies up to 7 TeV and 2.76 TeV, respectively. ALICE is one of the detector experiments optimised for heavy-ion collisions. A fixed-target experiment in ALICE is considered to collide a portion of the beam halo split by means of a bent crystal with an internal target placed a few meters upstream of the detector. Fixed-target collisions offer many physics opportunities related to hadronic matter and the quark-gluon plasma to extend the research potential of the CERN accelerator complex. This paper summarises our progress in preparing the fixed-target layout consisting of crystal assemblies, a target and downstream absorbers. We discuss the conceptual integration of these elements within the LHC ring, impact on ring losses, conditions for a parasitic operation and expected performance in terms of particle flux on target.
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HL-LHC: Project Status and Beam Dynamics Challenges
S. Redaelli
CERN, Geneva, Switzerland
The Large Hadron Collider (LHC) at CERN has been producing physics data since 2010. It will be upgraded in the years 2025-27 to sustain and further extend its physics discovery potential. The High-luminosity LHC upgrade (HL-LHC) targets at least a factor five increase of peak luminosity, and a ten-fold improvement of integrated luminosity, compared to the LHC design. To achieve this, the HL-LHC beams are two times more intense and more than five times brighter. These ambitious goals pose obvious beam dynamics challenges that will be addressed through several upgrades of the LHC accelerator. The HL-LHC will use high-field superconducting magnets based on Nb₃Sn for the final beam focusing, crab cavities to optimize luminosity conditions, a new generation of collimators that withstand the higher operational beam losses while reducing the beam impedance, hollow electron lenses for active halo control as well as crystal collimators for improved cleaning efficiency for heavy-ion beams. This advances the LHC state-of-the-art accelerator technology in various domains. This contribution reviews the plans and status of the HL-LHC upgrade and the main challenges associated with this project.
