An alignment method for the ATLAS end-cap TRT detector using a narrow monochromatic X-ray beam

The end-cap Transition Radiation Tracker (TRT), consisting of 36 modules (w heels), is being constructed as a part of the ATLAS Inner Detector at the C ERN LHC. This paper describes a method for determining the wire positions i nside the straw proportional tubes (SPT), which are the basic building bloc ks of the ATLAS TRT, with an accuracy of better than 10 mum. The procedure involves moving a narrow monochromatic X-ray beam across the straw and meas uring the counting rate as a function of the position of the X-ray beam in the straw. To achieve this goal, a Beam Directing Device (BDD), providing t he possibility to direct the X-ray beam in a chosen direction within some s olid angle and supplying an accurate angular measurement system, has been c onstructed. The results of the wire position measurements performed using t his BDD on a full-scale mechanical prototype end-cap wheel of the TRT are p resented in this paper. (C) 2001 Published by Elsevier Science B.V.