Cryogenic Beam Loss Monitoring for the LHC

A Beam Loss Monitoring (BLM) system was installed on the outside surface of the LHC magnet cryostats to protect the accelerator equipment from beam losses. The protection is achieved by extracting the beam from the ring in case thresholds imposed on measured radiation levels are exceeded. Close to the interaction regions of the LHC, it is challenging to distinguish between collision products and possible quench-provoking beam losses with the present BLM system. The situation can be optimised by locating beam loss monitors inside the cold mass of the magnets in superfluid helium, where high levels of radiation are expected. No existing technology was proven to work in such conditions. The new detectors need to be available, reliable and stable for 20 years. The performed measurements show that diamond and silicon detectors satisfy the criteria for use in a fast protection and feedback system, while the simultaneous use of the liquid helium chamber enables the calibration of the solid-state detectors and the reliable protection from steady state losses.