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A Large Area Micromegas TPC for Tracking at the ILC

Abstract : The study of the fundamental building blocks of matter necessitates always more powerful accelerators. New particles are produced in high energy collisions of protons or electrons. The by-Products of these collisions are detected in large apparatus surrounding the interaction point. The 125 GeV Higgs particle discovered at LHC will be studied in detail in the next e⁺e⁻ collider. The leading project for this is called ILC. The team that I joined is working on the R&D for a Time Projection Chamber (TPC) to detect the charged tracks by the ionization they leave in a gas volume, optimised for use at ILC. This primary ionization is amplified by the so-Called Micromegas device, with a charge-Sharing anode made of a resistive-Capacitive coating. After a presentation of the physics motivation for the ILC and ILD detector, I will review the principle of operation of a TPC (Chapter 2) and underline the advantages of the Micromegas readout with charge sharing. The main part of this PhD work concerns the detailed study of up to 12 prototypes of various kinds. The modules and their readout electronics are described in Chapter 3. A test-Bench setup has been assembled at CERN (Chapter 4) to study the response to a ⁵⁵Fe source, allowing an energy calibration and a uniformity study. In Chapter 5, the ion backflow is studied using a bulk Micromegas and the gas gain is measured using a calibrated electronics chain. With the same setup, the electron transparency is measured as a function of the field ratio (drift/amplification). Also, several beam tests have been carried out at DESY with a 5 GeV electron beam in a 1 T superconducting magnet. These beam tests allowed the detailed study of the spatial resolution. In the final test, the endplate was equipped with seven modules, bringing sensitivity to misalignment and distortions. Such a study required software developments (Chapter 6) to make optimal use of the charge sharing and to reconstruct multiple tracks through several modules with a Kalman filter algorithm. The results of these studies are given in Chapter 7. The TPC technique has been applied to neutron imaging in collaboration with the University of Lanzhou. A test using a neutron source has been carried out in China. The results are reported in Chapter 8.
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Wenxin Wang. A Large Area Micromegas TPC for Tracking at the ILC. Other [cond-mat.other]. Université Paris Sud - Paris XI, 2013. English. ⟨NNT : 2013PA112099⟩. ⟨tel-00854414⟩

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