3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Characterization of direct current discharge based electric microthrusters(2017) Wright, William PatrickIn this work, a novel electrostatic microthruster concept, based on a direct current gaseous discharge, is proposed. The design draws inspiration from the previously developed CorIon system, which utilizes a coupling of the corona ionization mechanism and the acceleration mechanism. The new design is an attempt to develop a space propulsion system for use on microsatellites, such as CubeSats. A proof of concept system is tested to determine if the direct current discharge can be used as a plasma generator for use in electric space propulsion systems. A system representative of the proposed microthruster concept is tested to determine if it operates in a way that will generate thrust, and boundaries on the systems stable operating parameters are ascertained. Lifetime, re- peatability and erosion tests are performed on both the proof of concept system, and the microthruster design to determine if the system is an improvement on the CorIon system. A thrust measurement stand is designed and constructed that utilizes a novel magnetic coupling mechanism to measure the thrust produced by a microthruster. The thrust measurement stand is tested with a cold gas thruster to study the thrust stands repeatability characteristics, and if it produces the expected results for such a system. A theoretical model for the thrust measurement stand is developed, so that the output of the thrust stand can be predicted for various loading conditions. Thrust measurements are performed on the microthruster design as different operating parameters are varied. Measurements of the power used by the microthruster design are taken as different op- erating parameters are varied. Ion current density measurements of the microthruster design are performed as different operating parameters are varied. Ion current density distribution measurements of the microthruster design are performed. Simulations of the microthruster design are developed, using COMSOL Multiphysics, to con rm the hypothesized mechanism of operation of the microthruster design, and to explain the trends observed in experimental data. Two types of simulation are constructed: a base case, where general features in the physical quantities extracted from the simulations are discussed, and simulations where operating parameters are varied, to study the effects these parameters have on the extracted physical quantities. Thrust values are extracted from the simulations and compared with the experimentally measured thrust. Future research to be conducted involving the novel microthruster design is listed.Item Electrical transport properties of nitrogen doped carbon microspheres(2014-07-22) Wright, William PatrickA suite of four samples of nitrogen doped carbon microspheres, each with a di erent level of nitrogen dopant, was synthesised in a horizontal chemical vapour deposition reaction. The samples were characterized using scanning electron microscopy, Raman spectroscopy and electron paramagnetic resonance spectroscopy. Scanning electron microscopy showed that microspheres were produced by the reaction. Raman spectroscopy con rmed the graphitic nature of the samples. Electron paramagnetic resonance spectroscopy determined that nitrogen was present in the graphitic lattice and was used as a non-destructive technique to measure the amount of substitutional nitrogen present in the samples. In order to perform electrical transport measurements an automated magneto-transport measurement station was developed in the laboratory. This transport station was computer controlled and contained all of the necessary hardware and software required to perform magneto-electrical transport measurements. Variable temperature electrical transport measurements were performed on all samples to determine their conductive properties. Resistance measurements showed that two of the samples were semiconductors while the other two samples displayed a transition to metallic behaviour at higher temperatures. This transition can be ascribed to the thermal desorption of nitrogen dopant. Models were tted to the data and the semiconducting behaviour is best explained by a model of uctuation induced tunnelling while the metallic behaviour is best explained by a quasi-1 dimensional metallic term based on electron-phonon interactions. The IV characteristics of two of the samples display increasing non-linearity of the current's voltage dependence with decreasing temperature. The other two samples exhibit this behaviour at lower temperatures while higher temperature IV data displays a current saturation with increasing voltage. The same models used to explain the resistance measurements can be used to explain the IV characteristics data extremely well. The magnetoresistance data taken with the direction of current ow orientated both parallel and perpendicular to the eld, show a transition from negative to positive magnetoresistance with decreasing temperature. The results of these experiments are inconclusive, as a theoretical model of magnetoresistance in systems that conduct via uctuation induced tunnelling is not well de ned. A comparison between the resistance measurements of all four samples was made to determine the e ect of nitrogen doping on the samples' electronic transport properties. The result of this comparison was indeterminate. This was due to samples with identical nitrogen dopant levels displaying vastly di erent conductive properties and indicates that very strict synthesis conditions need to be adhered to in order to ensure sample quality. Resistance measurements were rerun on the two samples that displayed purely semiconducting behaviour to investigate the possibility of atmospheric doping. It was found that the samples now displayed a transition to metallic behaviour and a reduced resistance. These results are suggestive of atmospheric doping by oxygen and water vapour.