These devices are used to monitor the beams intensity, the charge stripping efficiency, and transmission losses during delivery. Compared to the BPM's, BCM's have a faster detection time for larger beam currenty, but are slower for low current beams.
BCMs are located throughout the LINAC at key points on the beamline. A full comprehensive location guide can be found using the LINCAC status display pages, which can be found from the FE launch page.