Readout and control of optical alignment devices in the ATLAS muon endcap

Optical devices have been used to monitor the positions and deformations of the ATLAS Endcap Muon chambers in real-time during data-taking in a muon beam at CERN. A part of an octant of the ATLAS Muon endcap spectrometer has been set up in a test beam to study particle tracking precision. The scale of the ATLAS spectrometer and the high precision needed for particle momentum measurements (10% at 1000 TeV) require a continually operating optical system to track motions of the detector chambers. With alignment corrections applied the design tracking precision was achieved.