Research and development of a segmented GEM readout detector

Jagfeld, Christoph (2023): Research and development of a segmented GEM readout detector. Dissertation, LMU München: Fakultät für Physik

Abstract

Micro-Pattern Gaseous detectors are high-rate capable particle detectors. They show an excellent spatial and temporal resolution. Two types of them, GEM (Gas Electron Multiplier) and Micromegas (Micro-MEsh GAseous Structure) detectors are widely used in HEP experiments. This work combines both detector types to the novel Segmented GEM Readout (SGR) detector. The SGR detector uses a 2D Micromegas strip readout structure and a GEM foil whose copper coating on one or both sides is segmented into strips. This GEM foil replaces the micro-mesh of the Micromegas detector. Based on this new technology, up to two new readout strip layers are added to the detector, so that it has up to four readout strip layers in total. The SGR detector has two main advantages over the conventional Micromegas detector: Firstly, due to the geometry of the detector readout, one coordinate of the incident particle is determined more accurately than the other one. The signal of the GEM strips is used to compensate for this. Secondly, a unique 2D particle position reconstruction is only possible if the detector is hit by only one particle at the same time. If multiple particles arrive simultaneously a unique X-Y assignment is strongly aggravated. This can be compensated by GEM strips rotated 45° to the Micromegas strips. Simulations have shown a large reduction in ambiguities in the multiparticle reconstruction by turning the GEM strips by 45X to the Micromegas strips. Thus, the detector is read out at the GEM foil along an additional coordinate (U-coordinate), while the X and Y-coordinate are obtained by the Micromegas readout strip layers. The SGR detector is expected to be very well suited to determine the unambiguous 2D position of several particles simultaneously. The SGR prototype developed and built for this work uses GEM strips that are perpendicular to the strips of the upper Micromegas readout layer. At perpendicular incidence, the SGR detector provides an excellent energy (ΔE/E ≈ 10%) and position resolution (better than 80 mm). Even at a large incidence angle of 20X, the resolution remains better than 155 mm. In both cases, the 2D position reconstruction efficiency is well above 90 %. Additionally, this work provides a comprehensive description of the signal shapes observed in experiments, through extensive simulations using ANSYS and Garfield++. The results reveal significant differences in signal shapes among the various active detector layers. Bipolar signals are observed in both Micromegas readout coordinates and on the GEM strips when the segmentation faces the anode. If the segmented side faces toward the other direction, the signal on this layer is unipolar. The strong influence of electron motion on the highly resistive anode onto the properties and signal shapes of the Micromegas readout layers was elaborated in detail. The different accuracies of the two Micromegas readout strip layers were understood. Based on that suggestions for optimizations are provided. This work shows that the principle of an SGR detector works very well and the working principle is understood. Based on this work, the construction of an X, Y, U SGR detector is possible.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Keywords: Micromegas, GEM, Segmented GEM Foil, Micropattern Gaseous Detector,
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 16. Mai 2023
• 1. Bericht­erstatter:in: Biebel, Otmar