The next large collider to be build after the Large Hadron Collider LHC is the electron-positron International Linear Collider ILC. Both collider concepts complement each other. The LHC, reaching centre of mass energies of up to 14 TeV, has a high discovery potential, while the ILC with its well known initial state allows high precision measurements. A detector at the ILC will need a finely segmented calorimeter and a tracking detector with high efficiency and momentum resolution, as well as good particle identification. Currently there are four different concept studies trying to optimise the detector for the requirements at the ILC. In three of these detector concepts a time projection chamber (TPC) is foreseen as the main tracking device. A TPC allows the measurement of several hundred points per track, providing a very good tracking efficiency. With only 3% of a radiation length in the barrel region, the amount of material introduced into the detector is small compared to silicon sensors. This minimises multiple scattering and improves the energy measurement in the calorimeters. The TPC also provides a good measurement of the specific energy loss dE/dx for particle identification. To achieve the intended spatial resolution of 100 micrometres, micro pattern gas detectors (MPGD) are considered for gas amplification. These devices consist of structures with a size of a few hundred micrometres, in contrary to an anode wire readout with a pitch of typically a few millimetres. This improves the granularity of the measurement and minimises ExB effects, resulting in an enhanced spatial and two track resolution. Furthermore the backdrift of ions into the sensitive volume of the TPC is intrinsically suppressed. This is essential, as the established method of gating away the ions after each recorded event will not work at the ILC. Due to the bunch structure there will be data from 150 bunch crossings simultaneously in the TPC. The two different MPGDs discussed for the ILC TPC are Micro-Mesh Gaseous Detectors (Micromegas) and Gas Electron Multiplier foils (GEMs). The current thesis shows resolution studies with a TPC prototype equipped with a triple GEM readout structure. A hodoscope made up of silicon strip sensors gives a precision reference track, allowing an unbiased measurement of the spatial resolution. High statistics measurements have been conducted at the DESY test beam facility, which provides positrons with a tunable energy between 1 GeV and 6 GeV. Using the independent measurement of the hodoscope allows systematic studies of the homogeneity of the TPC's electric field. The fluctuations of the field in the chamber's central region were found to be DeltaE/E = 0.008. Field distortions have been determined and corrected, reducing the remaining deviations to a level well below the spatial resolution of the TPC. One important task is to reduce the number of ions drifting back into the sensitive volume. Special GEM settings with minimised ion backdrift have been examined with respect to their influence on the spatial resolution and it was found that the spatial resolution is not degraded using these special settings. The TPC at the ILC will be operated in high magnetic fields. Thus it is mandatory to show that the anticipated performance can be achieved in magnetic fields. The TPC prototype has been operated in a 4 T magnetic field, provided by a superconducting solenoid located at DESY Hamburg. Again the spatial resolution measured with the ion backdrift optimised settings is compared to that achieved with non-optimised settings. In both cases the measured resolution is approximately 130 micrometres.
info:eu-repo/classification/ddc/530, Physik, Zeitprojektionskammer, GEM, ILC, Prototyp, Homogenität, Ortsauflösung, Gas Electron Multiplier, TPC, time projection chamber, prototype, hodoscope, magnetic field, spatial resolution, homogeneity
Networked Digital Library of Theses and Dissertations
Publikationsserver der RWTH Aachen University