Detecting Impacts of Proton Beams on the LHC Collimators With Vibration and Sound Measurements

The 360 MJ stored energy of the 7 TeV LHC beams can seriously damage the beam line elements in case of accidental beam losses. Notably, the collimators will sit at 6 to 7 sigmas from the beam centre (1.2 to 1.4 mm) and will be hit and possibly damaged in case of failures, with a consequent degradation of the cleaning performance of the overall collimation system. The experience from operating machines shows that an a-posteriori identification of the damaged collimators from the observed performance degradation is extremely challenging. Collimator tests with beam at the SPS have shown that the impact of 450 GeV proton beams at intensities from 1010to 3x1013 could be detected by measuring sound and vibrations induced by the impacting beams.