DETECTION OF UNIDENTIFIED FALLING OBJECTS AT LHC

About 3600 Ionization Chambers are located around the LHC ring to detect beam losses that could damage the equipment or quench superconductingmagnets. The Beam Loss Monitors (BLMs) integrate the losses in 12 different time intervals (from 40μs to 83.8s) allowing for different abort thresholds depending on the duration of the loss and the beam energy. The signals are also recorded in a database at 1 Hz for offline analysis. Since the 2010 run, a limiting factor in the machine availability occurred due to unforeseen sudden losses appearing around the ring on the ms time scale. Those were detected exclusively by the BLM system and they are the result of the interaction of macro-particles, of sizes estimated to be 1-100 microns, with the proton beams. In this document we describe the techniques employed to identify such events as well as the mitigations implemented in the BLM system to avoid unnecessary LHC downtime.