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.