First Experience of Crystal Collimators During LHC Special Runs and Plans for the Future

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-𝛽* 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.