Résumé du preprint DAPNIA-04-508

Calibrations of two alignment sensors used in the ATLAS Barrel muon spectrometer
J.-Ch. Barrière, O. Cloué, B. Duboué, V. Gautard, C. Guyot, M. Fontaine, P. Perrin, P. Ponsot, Y. Reinert, J.-P. Schuller, Ph. Schune
ATLAS is a particle detector which is being built at CERN in Geneva. The muon detection system of ATLAS barrel part is made up among other things, of 600 chambers measuring 2 to 6 m2 and 30 cm thick. The chambers position must be known with an accuracy of 30m for translations and 100rad for rotations for a range of 5mm and 5mrad. In order to fulfil these requirements, we have designed and calibrated different optical sensors.
One of these sensors, called Praxial, is made with two optical alignment devices, called Rasnik (from Nikhef institute), positioned on two independent mechanical supports each one a two adjacent chambers. A Rasnik is simply a camera recording a chessboard mask image trough a lens, thus measuring with a high accuracy (<5m) the transverse position of the mask w.r.t. the optical axis. On our Praxial sensor, the two Rasnik are positioned with an angle permitting the spatial determination of one mechanical support w.r.t. the other one. So it can determine a chamber position with respect to its neighbouring.
Due to the accuracy required in the chambers position measurement, each type of sensor used in ATLAS must be calibrated on a particular calibration bench. Since we use Praxial sensors and other types of sensors, three PC based calibration bench was developed in our institute. In this conference, we will present the most complex one which combines: i) an ergonomic user interface, ii) motor control and temperature and position monitoring, iii) sequencing operation, iv) numerical analysis and v) database management. The software is now currently used for sensors calibration and more than 500 sensors have been calibrated.


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