Development of an optical alignment monitoring system for the ATLAS muon spectrometer

A novel electro-optical alignment monitoring system has been developed for the muon spectrometer of the ATLAS detector at the Large Hadron Collider. The basic components are multi-point straightness monitors which use semi-transparent optical sensors to measure the position of a traversing laser beam in several consecutive layers over large distances. This type of optical monitoring system provides economical solutions for a variety of alignment problems. Two types of custom designed optical position sensors have been tested which work on the principle of silicon strip photodiodes. Position resolutions of better than 2 μm and light transmission rates above 70% for suitable laser wavelengths have been achieved with prototype sensors. Improvement of the transmittance to about 90% is possible and in progress. (orig.)