Ποιοτικός έλεγχος και μελέτη των φυσικών και τεχνικών χαρακτηριστικών των σωλήνων και θαλάμων ολίσθησης MDT για την ανίχνευση μιονίων στο πείραμα ATLAS / LHC
Authors: Αβραμίδου Ραχήλ-Μαρία 
Published: August 2021

ATLAS (A Large Toroidal LHC Apparatus) is a general-purpose experiment, which will start its operation for physics at CERN (European Commission for Nuclear Research) in 2007. The ATLAS detector is designed to investigate many different physics processes, recording the products of the proton collisions at energies of 7 TeV per beam. The outermost part of the ATLAS detector, the Muon Spectrometer, is designed to identify with high efficiency muons, and measure their momenta with a resolution of ~10% at pΤ=1 TeV/c. The measurement is performed inside a toroidal field created by powerful toroid magnets with the help of the ATLAS Muon precision tracking system. The precision system consists mainly of ~370000 high pressure drift tubes (MDTs) assembled in ~1200 chambers. The design of the muon drift tubes aims to a high efficiency of 95-99% and an excellent spatial resolution of <80 μm (single wire resolution). Three Greek Universities have undertaken the responsibility to construct 30000 drift tubes of 1.67 m length (University of Athens), to test them (National Technical University of Athens) and finally assemble them into 120 BIS (Barrel Inner Small) chambers (University of Thessaloniki). The muon drift tubes are tested according to a quality assurance-quality control procedure. They have to fulfil certain requirements about the anode wire mechanical tension, the high voltage leak current, the gas leak and the anode wire position before they are assembled to chambers. My thesis is divided into three main concepts: i) the quality assurance and quality check (QA_QC) of the BIS-MDTs, ii) the quality assurance of four BIS-MDT chambers plus the modules-0 of other MDT chamber types at the CERN X-ray tomograph and iii) the cosmic ray data taken by a BIS-MDT chamber at the X5/GIF (Gamma Irradiation Facility) at CERN. In more details, the study, design, development, operation, automatisation and the data analysis of a first sample of these measurements for the BIS-MDTs, which took place at the High Energy Physics Laboratory of the National Technical University of Athens is the first part of this work. The construction quality of the assembled chamber is certified at the CERN X-ray tomograph, the key instrument for the ATLAS MDT chambers quality assurance and which is included in the second part of the thesis. It checks the chamber exceptional mechanical construction accuracy of better than 20 μm, which is needed in order that the required momentum resolution to be achieved. The achieved measurement accuracy of the X-ray tomograph is of 2 μm systematic and 2 μm statistical uncertainties in the horizontal and vertical directions in the whole working area, as it comes out after autocalibration measurements. The first four chambers of the Greek collaboration production series MDT-BIS have been measured and their results have been analyzed. The Modules-0 of all the different MDT construction sites have also been measured, in order that the correctness of the followed assembly procedure to be checked and certified. The last part of this work is focused on the operation and efficiency studies of the module-0 MDT-BIS chamber, which has been put at the X5/GIF at CERN, where muon cosmic rays measurements have been taken, under different operation conditions. The data analysis includes typical TDC spectra, autocalibration procedure, track reconstruction, spatial resolution and efficiency of the MDTs. Moreover measurements and data analysis of the hodoscope used as a trigger system have been performed. Extensive studies by GARFIELD simulation program of the muon drift tube parameters and performance are also presented. The conclusion extracted from the data analysis is that the chamber meets the ATLAS Muon Spectrometer requirements; it has low noise levels, uniform drift properties good spatial resolution and efficiency. These data analysis will also be used as a reference for the next series of measurements, including cosmic muon measurements, under the gamma source background for the chamber performance in a radiation environment, simulating the LHC conditions, and ageing studies.