Radiation Tolerance of Cryogenic Beam Loss Monitor Detectors

At the triplet magnets, close to the interaction regions of the LHC, the current Beam Loss Monitoring system is sensitive to the particle showers resulting from the collision of the two beams. For the future, with beams of higher energy and intensity resulting in higher luminosity, distinguishing between these interaction products and possible quench-provoking beam losses from the primary proton beams will be challenging. Investigations are therefore underway to optimise the system by locating the beam loss detectors as close as possible to the superconducting coils of the triplet magnets. This means putting detectors inside the cold mass in superfluid helium at 1.9 K. Previous tests have shown that solid state diamond and silicon detectors as well as liquid helium ionisation chambers are promising candidates. This paper will address the final open question of their radiation resistance for 20 years of nominal LHC operation, by reporting on the results from high irradiation beam tests carried out at CERN in a liquid helium environment.