Cryogenic Beam Loss Monitors for the Superconducting Magnets of the LHC

The Beam Loss Monitor detectors close to the interaction points of the Large Hadron Collider are currently located outside the cryostat, far from the superconducting coils of the magnets. In addition to their sensitivity to lost beam particles, they also detect particles coming from the experimental collisions, which do not contribute significantly to the heat deposition in the superconducting coils. In the future, with beams of higher energy and brightness resulting in higher luminosity, distinguishing between these interaction products and dangerous quench-provoking beam losses from the primary proton beams will be challenging. The system can be optimised by locating beam loss monitors as close as possible to the superconducting coils, inside the cold mass in a superfluid helium environment, at 1.9 K. The dose then measured by such Cryogenic Beam Loss Monitors would more precisely correspond to the real dose deposited in the coil. The candidates under investigation for such detectors are based on p+-n-n+ silicon and single crystal Chemical Vapour Deposition diamond, of which several have now been mounted on the outside of cold mass of the superconducting coil in the cryostat of the Large Hadron Collider magnets. This contribution will present the mechanical and electrical designs of these systems, as well as the results of their qualification testing including results of a cryogenic irradiation test.