Beam Conditions Monitor (ATLAS)

The ATLAS Beam Conditions Monitor (BCM) serves to protect the ATLAS detector from radiation damage caused by uncontrolled beam behaviour. It consists of two stations of detectors located near the beampipe in the forward and backward direction, at $z = \pm 184$ cm and $r = 55$ mm (corresponding to a pseudorapidity of about 4.2). The stations are equipped with fast electronics (2 ns rise time), measuring the time-of-flight and pulse height to distinguish events resulting from lost beam particles from those normally occurring in proton-proton interactions. The BCM also provides a measurement of bunch-by-bunch luminosities in ATLAS by counting in-time and out-of-time collisions.

Each BCM station consists of four modules; each module includes two diamond sensors read out in parallel. The sensors are required to tolerate doses up to 500 kGy and in excess of 10¹⁵ charged particles per cm² over the lifetime of the experiment.