This thesis has studied CO2 reforming of CH4 in atmospheric pressure, non-thermal plasma discharges. The objective of this research was to improve the current understanding of plasma-catalytic interactions for methane reforming. Chapter 1 introduces the existing and potential applications for methane reforming products. The industrial approaches to methane reforming and considerations for catalyst selection are discussed. Chapter 2 introduces non-thermal plasma technology and plasma-catalysis. An introduction to the analytical techniques used throughout this thesis is given. Chapter 3 investigates the effects of packing materials into the discharge gap. The materials were found to influence the reactant conversions for dry reforming of methane in the following order: quartz wool > no packing > Al2O3 > zeolite 3A > BaTiO3 > TiO2. In addition to the dielectric properties, the morphology and porosity of the materials was found to influence the reaction chemistry. The materials also affected the electrical properties of the plasma resulting in surface discharges, as opposed to a filamentary discharge mode. Chapter 4 investigates the effects of variation in CH4/CO2 ratios on plasma-assisted dry reforming of CH4. Differences in the reaction performance for different feed gas compositions are explained in terms of the possible reaction pathways and the electron energy distribution functions. A NiO/Al2O3 catalyst is introduced for plasma-catalytic dry reforming of CH4, which was found to have no significant effect on the reaction performance at low specific input energies. Chapter 5 presents the plasma-assisted reduction of a NiO/Al2O3 catalyst by CH4 and H2/Ar discharges. When reduced in a CH4 discharge, the active Ni/Al2O3 catalyst was effective for plasma-catalytic methane decomposition to produce H2 and solid carbon filaments. A decrease in the breakdown voltage was observed, following the catalyst reduction to the more conductive Ni phase. Chapter 6 investigates the performance of the plasma-reduced Ni/Al2O3 catalysts for plasma-catalytic dry reforming of methane. Whilst the activity towards dry reforming of CH4 was low, the CH4 plasma-reduced catalyst was found to be effective for catalysing the decomposition of CH4 into H2 and solid carbon filaments; both potentially useful products. Chapter 7 discusses further work relevant to this thesis.

The application of Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) to the determination of total oxygen, nitrogen and sulphur in organic solution has been studied. Near-infrared emission lines of the three nonmetals have been used and detection limits in xylene have been established. Oxygen was determined for the first time by ICP-OES in a nongaseous sample. The characteristics of the inductively coupled plasma when used with an organic aerosol have been studied with respect to the completeness of atomization and potential interference from the complex excitation environment. Spatially resolved atomic and molecular emission profiles have been collected as part of these investigations. The nonmetal emission intensities were found to depend on the boiling point of the compounds containing the nonmetal because a redistribution effect in the nebulizer chamber was leading to an enrichment of volatile solutes in the aerosol stream to the plasma. Response factors for a series of compounds have been determined. The utility of the method was shown by establishing working curves and by testing certified standards for sulphur. / Science, Faculty of / Chemistry, Department of / Graduate

Shock waves generated by laser-driven ablation in solids have provided a great opportunity for the study of dense plasmas. The work presented in this thesis include measurements of Hugoniot curves and the reflectivity of shocked aluminum. In these experiments, planar aluminum targets were irradiated with a 0.53µm, 2ns (FWHM) laser pulse at irradiances up to ~ 10¹⁴/cm². Temporally and spectrally resolved measurements of the target rear surface luminous emission have yielded the shock speed and temperature Hugoniot curve which showed good agreement with equation of state predictions. In addition, temporally resolved reflectivity measurements of the shocked target rear surface compared well with a theoretical model for the electrical conductivity of a dense plasma. For copper and molybdenum targets, both the luminescence and the reflectivity measurements indicated that the heating of the dense target material was dominated by radiation transport from the coronal plasma rather than shock heating. An analysis of the molybdenum results indicate that x-ray shine-through may be the dominant energy transport mechanism to the target rear surface, whereas for the copper targets the transport process appears to be much more complex. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Improvements to the laser excited interferometer previously constructed in this laboratory are described. The use of a rotating retro-reflector in the interferometer cavity, and electronic circuitry, permit direct recording of electron densities. The sensitivity of the interferometer is 5 x 1015 cm-2, and the temporal resolution is 0.1 usee. Pyrex tubes, terminated by windows, enclosing the laser beam, have been used to improve spatial resolution. The effects of the tubes, and of all other sources of error associated with interferometric measurements of electron densities, have been carefully assessed. A Z-pinch discharge in 4 torr helium has been studied with this instrument, and with spectroscopic determinations of electron temperature. Under the conditions chosen, the pinching plasma does not reach the axis of the discharge tube, but stops at a radius of 2.7 cm. The shock front caused by the pinching action has been shown to be weak. Longitudinal structure, due to heat flux, characteristic cathode behaviour, and variations in timing of the pinching action, has been found. The discharge has been assessed as a spectroscopic source and as a medium for laser scattering experiments. The characteristics of two suitable regions are presented. These are the axial region and the hollow cylinder of plasma formed by the arrest of the pinching plasma. Both are free of instabilities. At the appropriate time the latter is also current free, and shows longitudinal electron density variations of less than 2%. The length of time that the current spends near the wall of the vessel is determined by the balance between kinetic and magnetic pressures. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Experimental profiles of the He II lines at 3203 Å and 4686 Å have been obtained from a well diagnosed helium plasma. The plasma was produced in a low power z-pinch discharge contained in a vessel of 15 cm diameter and 60 cm length. Uniform plasma columns were located and studied by means of two moveable quartz limiter tubes. The effect of the tubes on the measured electron temperature and density due to cooling and evaporated impurities was measured and the tubes were positioned so as to select a uniform plasma column for study. Electron temperatures were determined from the intensity ratio of the lines He II 4686 and He I 5876 using a theory that considered finite escape probabilities for the Lyman a resonance photons. Electron densities were determined from the width of the He I 5876 line. Corrections were applied for ion broadening due to doubly charged ion perturbers. An electron temperature of 4.0±0.4 eV and an electron density of (6 .1 ±0.6) xl 0 2 3m"^;.wlere determined for the axial plasma occurring soon after the pinch phase. The experimental profile of He II 4686 as measured by a spectrometer-optical multichannel analyzer arrangement was compared to theoretical profiles resulting from a treatment of the electron broadening collisions as single event impacts (Kepple (1972)) and from a treatment of the electron broadening which considers the time development in the collision process (unified classical-path theory) (Greene (1976)). The experimental profile was found to lie midway between the theoretical profiles. Agreement between the experimental and unified classical-path profi1e in the near line wings was good. Agreement between experimental and electron impact results for He II 3203 was not good with a 60% disagreement in line widths. The He II line had a double peak with the peak at shorter wavelengths being 9% higher than the other peak. This is similar to the behavior observed in the Balmer line, Hβ, in the atomic hydrogen spectrum. / Science, Faculty of / Physics and Astronomy, Department of / Unknown

A Z-pinch plasma, suitable for the study of C0₂ laser-plasma interaction mechanisims, is thoroughly diagnosed using a number of non-perturbing, optical probe techniques. Simple streak and shadow methods give an important preliminary view of the spatial distribution and radial dynamics of plasma during the high compression phase. The electron density and temperature are determined as a function of time by spectrally resolving the ion feature of Thomson scattered ruby laser light. Peak electron densities well in excess of 1 x 10¹⁹ cm⁻³ and temperatures near 50 eV are observed. Complementing the scattering results, holographic interferometry is performed to examine both the temporal and spatial variation of electron density. The diagnostics used are well suited to the examination of moderately dense, hot plasma and have been developed specifically for application in our laser-plasma interaction studies. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

<p> This dissertation describes experiments in spherical Couette devices, using both gas and liquid sodium. The experimental geometry is motivated by the Earth's outer core, the seat of the geodynamo, and consists of an outer spherical shell and an inner sphere, both of which can be rotated independently to drive a shear flow in the fluid lying between them. In the case of experiments with liquid sodium, we apply DC axial magnetic fields, with a dominant dipole or quadrupole component, to the system. We measure the magnetic field induced by the flow of liquid sodium using an external array of Hall effect magnetic field probes, as well as two probes inserted into the fluid volume. This gives information about possible velocity patterns present, and we extend previous work categorizing flow states, noting further information that can be extracted from the induced field measurements. The limitations due to a lack of direct velocity measurements prompted us to work on developing the technique of using acoustic modes to measure zonal flows. Using gas as the working fluid in our 60 cm diameter spherical Couette experiment, we identified acoustic modes of the container, and obtained excellent agreement with theoretical predictions. For the case of uniform rotation of the system, we compared the acoustic mode frequency splittings with theoretical predictions for solid body flow, and obtained excellent agreement. This gave us confidence in extending this work to the case of differential rotation, with a turbulent flow state. Using the measured splittings for this case, our colleagues performed an inversion to infer the pattern of zonal velocities within the flow, the first such inversion in a rotating laboratory experiment. This technique holds promise for use in liquid sodium experiments, for which zonal flow measurements have historically been challenging.</p>

Orientador: Munemasa Machida / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica, Gleb Wataghin / Made available in DSpace on 2018-08-14T10:48:49Z (GMT). No. of bitstreams: 1 Nascimento_Fellypedo_M.pdf: 4493365 bytes, checksum: 50c2d66d1ba6fb6004585fe057e964e5 (MD5) Previous issue date: 2009 / Resumo: Neste trabalho, foram feitas medidas simultâneas e três linhas e emissão e hidrogênio no tokamak NOVA-UNICAMP. A partir das medidas e brilho as emissões das linhas Ha , H b e Hg e fazendo uso de coeficientes que constam nas tabelas de Johnson e Hinnov, foi possível determinar temperaturas e densidades eletrônicas no plasma ao longo de descargas o tokamak. Para isto, foi utilizada, e aperfeiçoada, uma técnica desenvolvida num trabalho e doutoramento recente do nosso grupo, a qual faz uso do conceito de unicidade do tempo de confinamento de partículas. Os principais aprimoramentos realizados neste diagnóstico foram: utilização de três espectrômetros para medidas simultâneas das emissões e hidrogênio, instalação e fibras ópticas para coletar a luz emitida pelo plasma, adoção de um sistema de colimação para obter um certo grau e definição espacial nas medidas, uso de um maior número e valores e temperaturas na análise dos dados e desenvolvimento de um novo método (algorítimo) para obter os valores de temperaturas e densidades dos elétrons no plasma. As temperaturas e densidades eletrônicas médias obtidas ficaram em torno e 7,5 eV e 7,0 ·10 12cm-3, respectivamente. Estes valores estão entro do espera o para tais parâmetros na borda do tokamak NOVA-UNICAMP. Isto indica que este diagnóstico pode ser usado para monitorar ensidades e temperaturas e elétrons em plasmas gerados por tokamaks. Além isso, foram efetuados alguns experimentos com detectores multicanal e o gás hidrogênio foi trocado pelo hélio, na tentativa de mostrar a versatilidade do diagnóstico proposto. / Abstract: In this work, we have made simultaneous measurements of three hydrogen emission lines on our tokamak. From the measurements of absolute brightness of the Ha , H b e Hg lines an using data from Johnson an Hinnov table, was possible to determine electronic ensities an temperatures during the tokamak ischarges. For this,we have used, an refined, a technique developed in a recent PhD thesis in our work group. This technique uses the concept of particle confinement time uniqueness. The main upgrades made in this diagnostic were: the use of three spectrometers for simultaneous measurements of the hydrogen emissions, installation of optical fibers to collect the light emitte by the plasma, adoption of a collimation system for having some spatial definition of the measurements, use of a greater range of temperature values uring the data analysis and development of a new method (algorithm) for obtaining the electronic densities and temperatures in the plasma. The average temperature and density obtained was about 7.5 eV and 7.0 ·1012cm-3, respectively. The results obtained are in accordance with the expected values for these parameters at the edge of the NOVA-UNICAMP tokamak plasma. This indicates that this diagnostic can be used to monitor the electronic densities and temperatures in tokamak plasmas. Additionally, we have made experiments with multichannel detectors, and the hydrogen gas was replaced by helium, in an attempt to show the versatility of the proposed diagnostic. / Mestrado / Física / Mestre em Física

No description available.

Orientador: Paulo Hiroshi Sakanaka / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-15T14:36:05Z (GMT). No. of bitstreams: 1 Shigueoka_Hisataki_M.pdf: 1368862 bytes, checksum: 56bdde0fb29d4ffe959e15f4fa0c47bd (MD5) Previous issue date: 1977 / Resumo: O objetivo deste trabalho é mostrar a influência da toroidicidade na estabilidade de plasmas em sistemas toroidais tipo tokamaks com seção circular. Usando a equação de movimento da teoria magnetohidrodinâmica ideal expandida em A-l pequeno, onde A é a razão de aspecto de toróide definida como razão entre o raio maior com raio menor de toráide, como foi feito por Copenhaver( 1976 ), desenvolveu-se um programa computacional pelo método de tiro ao alvo. Calculou-se a variação da razão de crescimento de modos instáveis em função da razão de aspecto para perfis de Suydam estável e instável. Observou-se que existem duas classes de kink, m = 1, para tokamaks de baixo - b. A primeira, modo kink interno surge quando o fator de fuga q no eixo magnética está abaixo de unidade, q( 0 ) < 1, e a sua razão de crescimento decresce com o aumento da toroidicidade. A outra, modo kink central, surge quando o fator de fuga q no eixo magnético é aproximadamente igual a um e a razão de crescimento cresce com o aumento do efeito toroidal. Estes modos.instáveis existem independente da estabilidade Suydam / Abstract: Not informed. / Mestrado / Física / Mestre em Física