Thesis (Ph. D.)--City University of Hong Kong, 2005. / "Submitted to Department of Physics and Materials Sciences in partial fulfillment of the requirements for the degree of Philosophy of Doctor." Includes bibliographical references.

Thesis (M.S.)--Rochester Institute of Technology, 1990. / Typescript. Includes bibliographical references (leaves 72-75).

Thesis (M.S.)--University of Texas at Dallas, 2008. / Includes vita. Includes bibliographical references (leaves 86-87)

The cylindrical column of plasma produced in the first stage of a z-pinch discharge is theoretically unstable. For one particular type of instability, the amplitude of a surface perturbation increases at a rate dependent on the acceleration of the surface (Rayleigh-Taylor instabilities). An experimental study of these instabilities has been carried out by photographing the discharge column with a high-speed framing-camera. Simple rotationally symmetric instabilities have been excited in the normally stable initial stage of an argon z-pinch discharge by means of a set of equally spaced glass rings. The framing camera photographs show that the instabilities develope approximately in accordance with the Rayleigh-Taylor theory. No axial drift of the instabilities is observed, but the new technique of studying instabilities reveals that the acceleration of the discharge boundary changes appreciably three or four times during the initial stage of the discharge. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The work contained in this thesis is concerned with the elucidation of the growth mechanism responsible for the formation of silicon dioxide by plasma anodization. Three possible theories for the growth mechanism have been considered; namely, (1) the rate-limiting diffusion theory (2) the classical theory of high-field ionic conduction and (3) the impact ionization theory. The verification of the applicability of any of the above three theories required the design and construction of (a) an in situ film thickness measuring system and (b) a plasma anodization system capable of controlling the substrate temperature. The experimental data could not be accounted for by either the rate-limiting diffusion or high-field ionic conduction theories, but good agreement was found with predicted results from an impact ionization theory. The development of a suitable impact ionization theory yielded a value for the electron mobility in SiO₂ which was almost identical to the average value calculated from recent Hall effect measurements. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Electrical discharge is a commonly used method to produce ions and radicals that can be used for degrading compounds as well as for chemical synthesis. Previously, the application of electrical discharges has been studied in liquids such as water and alcohols to produce hydrogen peroxide and hydrogen and to destroy organic compounds in the water and gas phases. Recently low power gas-liquid electric discharges have been employed to increase efficiency for hydrogen peroxide and oxidized products for synthesis or degradation. Determination and analysis of the intermediate radicals produced in the plasma has not been studied intensively for discharges at the gas-liquid interface such as aerosol sprays and thin liquid films. According to theoretical models based on reaction kinetics in plasma these radicals such as hydroxyl radicals play an important role in formation of hydrogen peroxide. However, there may be excess hydroxyl radicals formed and not involved in the formation of hydrogen peroxide. The main goal of this work is to characterize and identify key intermediate radicals and their reaction pathways in the liquid phase, gas phase, and at the interface of these aerosol droplets and thin film surfaces using various gases and liquid feeds. / A Dissertation submitted to the Department of Chemical and Biomedical Engineering in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Spring Semester, 2015. / March 17, 2015. / advanced oxidation processes, electrical discharge, Fenton reaction, hydrogen peroxide, hydroxyl radical, plasma / Includes bibliographical references. / Bruce R. Locke, Professor Directing Dissertation; Igor Alabugin, University Representative; Ravindran Chella, Committee Member; Rufina Alamo, Committee Member.

The central purpose of this thesis is to explore the behavior of the numerical solution of the Cold- Ion model with shock forming conditions in one and two dimensions. In the one dimensional case, a comparison between the numerical solution of the Vlasov equation is made. It is observed that the Cold-Ion model is no longer representative of the cold-ion limit of the Vlasov-Poisson equation when a spike forms in the solution. It was found that the lack of a spike in the solution of the Cold-Ion model does not necessarily mean that a bifurcation has not formed in the solution of the Vlasov-Poisson equation. It was also determined that the spike present in the solution of the one dimensional problem appears again in the two dimensional simulation. The findings presented in this thesis opens up the question of determining which initial and boundary conditions of the Cold-Ion model causes a shock to form in the solution. / A Thesis submitted to the Department of Scientific Computing in partial fulfillment of the requirements for the degree of Master of Science. / Fall Semester, 2014. / October 15, 2014. / Cold-Ion, Plasma, Shocks, Vlasov-Poisson / Includes bibliographical references. / Max Gunzburger, Professor Directing Thesis; Janet Peterson, Committee Member; Sachin Shanbhag, Committee Member.

The first large-scale study of magnetically-confined plasma for the production of fusion energy is scheduled to begin this decade and will answer many questions. Two critical issues are: (1) how to control and prevent non-axisymmetric magnetic perturbations that may drive harmful current and plasma energy into the surrounding walls, and (2) how to understand the relationship between plasma rotation, plasma confinement, and plasma stability. To address both, this dissertation reports research with biasable electrode arrays in the HBT-EP tokamak. This work conducts systematic studies of driven current and achieves the first active control of plasma rotation and rotating magnetic instabilities with a toroidal electrode array. Electrode-driven current impacts the plasma in several ways. First, it can increase, decrease, and reverse plasma rotation as measured by Mach probes, which results in an altered radial electric field. By controlling the electrode voltage with an active feedback system, plasma rotation is controlled between 4 and 8 kHz. Second, by modulating the driven electrode current at fixed frequencies, spontaneous magnetic perturbations develop at the plasma’s edge. These distortions are field aligned, do not rotate, and match the magnetic helicity of the scrape-off-layer (SOL). Direct measurement of SOL current to collectors mounted on the wall, show that the SOL current is field-aligned with a filamentary structure. When a naturally-occurring rotating m=2 mode is present, magnetic measurements show that the two structures are superimposed with no obvious indication of coupling. Third, when the electrode current is driven at the natural frequency of rotating magnetic perturbations, the plasma’s proportional response increases, indicating a resonance at 9 kHz. Resonance is observed in the radial electric field, floating potential profile, plasma rotation, and magnetic measurements. Finally, when the electrode array is biased in quadrature and actively controlled, driven currents modify the rotation and amplitude of the long-wavelength rotating magnetic modes. When the quadrature electrode array is phase locked to the n=1 mode rotation, mode amplitudes are suppressed by as much as 50%. Suppression shows a clear dependence on a phase between the rotating mode and the driven current. These experiments show that the structure of SOL currents are field-aligned and demonstrate a clear relationship between biased-electrode driven current and the rotation and amplitude of helical magnetic perturbations.

The objective of this thesis was the design of a regeneratively cooled, high temperature, clean gas plasma generator facility. This facility was desired to extend the high temperature research capabilities of the Department of Mechanical Engineering.

Fossil resources provide the raw materials for manufacturing a majority of commodity chemicals and fuels, but the release of this buried carbon accelerates environmental crises related to rising levels of atmospheric CO2. Engineering direct and energy-efficient pathways to synthesize chemicals and fuels from sustainable reagents and using CO2-free renewable energy could mitigate these challenges. Promising strategies for developing such reaction processes utilize non-precious metal catalysts to address kinetic challenges and non-thermal plasma activation to circumvent thermodynamic constraints. Non-precious bimetallic catalysts were employed to selectively convert CO2 with H2 to the building block chemical CO, and in situ X-ray and infrared techniques revealed the properties of the catalytic components. Significant oxygen exchange between the ceria catalyst support material and gas-phase CO2 was quantified under reaction conditions, and NiFe bimetallic catalysts tuned the reaction selectivity while maintaining high activity. In order to eliminate H2 as a reagent, ethane (an underutilized shale gas fraction) was reacted with CO2 to produce alcohols. This reaction is not thermodynamically feasible under mild conditions, so non-thermal/non-equilibrium plasma activation was implemented in order to achieve a one-step, H2-independent process to synthesize alcohols and other oxygenates under ambient temperature and pressure. The ability to use non-thermal plasma to activate N2 at mild conditions introduces the possibility of moving beyond the carbon-based paradigm for chemicals and fuels. Non-thermal plasma has been used to synthesize ammonia under mild conditions, but the dearth of fundamental understanding of plasma-catalyst interactions handicaps the development of plasma catalytic N2 conversion processes. Therefore, an in situ FTIR reactor was employed to identify the surface reaction intermediates during plasma catalytic ammonia synthesis. These results provide the first direct evidence of catalytic surface reactions under plasma activation and reveal the presence of reaction pathways that are distinct from analogous thermocatalytic reactions. Finally, an energy-based analysis evaluates the environmental and economic outlook for plasma-activated nitrogen fixation processes.