Crystal-assisted Collimation Experiment from the SPS to the LHC

UA9 was operated in the CERN-SPS for more than six years in view of investigating the feasibility of the halo collimation assisted by bent crystals. Two-millimeter-long silicon crystals, with bending angles of about 150 μrad, are used as primary collimators. The crystal collimation process is obtained consistently through channeling with high efficiency, showing a steady reduction of almost one order of magnitude of the loss rate at the onset of the channeling process. This result holds both for protons and for lead-ions. The corresponding loss map in the accelerator ring is accordingly reduced. These observations strongly support our expectation that the coherent deflection of the beam halo by a bent crystal should enhance the collimation efficiency also in LHC. After a concise description of the results collected in the SPS we propose a scenario to integrate bent crystals in the LHC collimation system for machine experiment.