Development of floating strip micromegas detectors

Micromegas are high-rate capable, high-resolution micro-pattern gaseous detectors. Square meter sized resistive strip Micromegas are foreseen as replacement of the currently used precision tracking detectors in the Small Wheel, which is part of the forward region of the ATLAS muon spectrometer. The replacement is necessary to ensure tracking and triggering performance of the muon spectrometer after the luminosity increase of the Large Hadron Collider beyond its design value of $10^{34}$\,cm$^{-2}$s$^{-1}$ around 2020. In this thesis a novel discharge tolerant floating strip Micromegas detector is presented and described. By individually powering copper anode strips, the effects of a discharge are confined to a small region of the detector. This reduces the impact of discharges on the efficiency by three orders of magnitude, compared to a standard Micromegas. The physics of the detector is studied and discussed in detail. Several detectors are developed: A $6.4\times6.4\,$cm$^2$ floating strip Micromegas with exchangeable SMD capacitors and resistors allows for an optimization of the floating strip principle. The discharge behavior is investigated on this device in depth. The microscopic structure of discharges is quantitatively explained by a detailed detector simulation. A $48\times50\,$cm$^2$ floating strip Micromegas is studied in high energy pion beams. Its homogeneity with respect to pulse height, efficiency and spatial resolution is investigated. The good performance in high-rate background environments is demonstrated in cosmic muon tracking measurements with a $6.4\times6.4\,$cm$^2$ floating strip Micromegas under lateral irradiation with 550\,kHz 20\,MeV proton beams. A floating strip Micromegas doublet with low material budget is developed for ion tracking without limitations from multiple scattering in imaging applications during medical ion therapy. Highly efficient tracking of 20\,MeV protons at particle rates of 550\,kHz is possible. The reconstruction of the track inclination in a single detector plane is studied and optimized. A quantitative description of the systematic deviations of the method is developed, that allows for correcting the reconstructed track inclinations. The low material budget detector is tested in therapeutic proton and carbon ion beams at particle rates between 2\,MHz and 2\,GHz. No reduction of the detector up-time due to discharges is observed. The measurable pulse height decreases by only 20\% for an increase of particle rate from 2\,MHz to 80\,MHz. Efficient single particle tracking is possible at flux densities up to 7\,MHz/cm$^2$. The good multi-hit resolution of floating strip Micromegas is shown.

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Development of floating strip micromegas detectors is an episode from Fakultät für Physik - Digitale Hochschulschriften der LMU - Teil 04/05 by Ludwig-Maximilians-Universität München.

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This episode was published on Apr 28, 2014.

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