The future LHC experiment, ATLAS, features a muon spectrometer in which the alignment system must control the spatial position of the muon chambers with an accuracy of 30 μm and 200 μrad in a range of displacements of ± 5 mm and ± 5 mrad. The alignment system described in this paper, called praxial, fulfils these requirements. The paper reviews the relative and absolute calibration procedures and the production of the 1005 praxial sensors needed in ATLAS.
We have developed an optical system which permits the absolute positioning of an element with respect to a reference laser beam. The resolution is of the order of 10 micrometer in translation and 50 (mu) rad in rotation. It is highly transparent (greater than 90%) permitting several elements to be aligned. A calibration procedure has also been studied in order to be independent of internal deformations.
A new type of highly transparent (95%) two dimensional position sensor has been developed which allows the accurate positioning (below 10 micrometers r.m.s.) of successive elements to which each sensor is attached, transversely to a laser beam used as a reference straight line. The present useful area of the sensor is about 15 X 15 mm2, and can be further increased.
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