Collimator upgrades toward HL-LHC
3D drawing of the by-pass cryostat/collimator assembly designed to install a warm collimator in the cold dispersion suppressor between two 11 T dipoles that would replace a standard dipole. Image credit: A. Bertarelli (CERN).
In the frame of the LHC upgrades towards the High Luminosity LHC (HL-LHC), the improvement of the LHC collimation system is a critical aspect. The Achromatic Telescopic Squeezing (ATS) optics, foreseen to be used in the HL-LHC, introduces major changes to the optics in the experimental Interaction Regions (IR).
The development carried out within the HiLumi LHC Work Package 5 aims at verifying that the cleaning of beam halo (the safe and controlled removal of the unavoidable beam losses by collimators during standard operation) and losses in the high-luminosity experimental regions remain appropriate for all the HL-LHC challenges, including higher beam stored energies and optics layout changes. Proposed collimation upgrades in Long Shutdown 1 (LS1) and LS2 are designed to be compatible already with the ultimate HL-LHC requirements.
Large losses are created by the collisions inside the LHC experiments. These so-called "Physics debris" losses have to be studied separately from beam halo matters in order to make sure that the local protection of the cold magnets downstream of the experiments is appropriate, i.e. that they can operate below the quench limit and that radiation damage remains under control. The studies performed so far indicated that the proton beam operation in IR1 and IR5 until LS3 could be compatible with the expected LHC parameters with an upgrade layout proposed for implementation in LS1. On the other hand, collision losses during ion beam operation will induce losses well above the quench limit of superconducting magnets in the dispersion suppressor. This calls for an action that might be already taking place in LS2, with priority given to IR2 where the ALICE detector is installed.
