A pressurized hydrogen plasma jet is developed for pressure broadening experiments at pressures of from 4 to -20 atmospheres. Operation at low flow rates produced a plasma which was homogeneous in cross section with respect to electron density and temperature, with axial gradients, well suited for broadening experiments. The broadening of two Sil lines, X3905 Å and A2881 Å was studied. Widths and shifts due to broadening by electrons (Stark effect) and also by neutral hydrogen atoms were measured. The experimental results were compared with the theory of Griem in the case of the Stark broadening and with the Unsold theory of Van der Waals broadening for the case of the hydrogen perturbers. Comparison is also made between the experimental results and other experimental results for broadening by argon atoms. Significant disagreement was found, especially in the case of the broadening by hydrogen atoms. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Theoretical and experimental studies have been made of the propagation characteristics of helicon waves in metallic spheres; the helicon wave is a branch of the magnetoplasma wave spectrum in the presence of a uniform, static magnetic field. Our theoretical considerations have shown that for an infinitely conducting sphere the helicon wave inside the sphere can be described to good approximation by a single cylindrical wave. This model leads to a simple, approximate, analytic understanding of the resonant mode structure and of the helicon field distribution inside the sample. The resonant modes can be described as a doubly infinite series, labelled by (m,n), where m indicates the number (odd) of half wavelengths along the magnetic field direction nearly equalling the sample diameter and n indicates the same condition perpendicular to the magnetic field. An exact numerical calculation for a sphere of finite scalar resistivity has been carried out by representing the helicon wave inside the sphere by a superposition of cylindrical waves. In this way one is able to calculate the absorption peak heights and widths as well as the resonant frequencies for the first few modes. These results are found to be in good agreement with those calculated independently by Ford and Werner using vector spherical harmonics throughout. Whereas the formalism of Ford and Werner is preferred for computational accuracy, their approach is physically less transparent. Experimentally, we have substantiated the results of the calculations by using single-crystal spheres of aluminium with a residual resistance ratio of about 4000. The resonant modes were studied for two distinct geometries of the excitation and detection coils: the "parallel" geometry had the axes of the coils collinear but at right angles to the static magnetic field, whereas the "perpendicular" geometry had the excitation coil, the detection coil and the magnetic field all mutually perpendicular. The anisotropy of the fundamental (1,1) absorption peak amplitude is about 20% and that of the resonant frequency is about 1% for an applied magnetic field of 35 k0e. The helicon data are interpreted in terms of the anisotropics of the transverse magnetoresistivity (20%) and of the Hall coefficient (1%). For the first time in a helicon experiment an adequate sampling of crystallographic orientations has been made using the same sample throughout. The principal feature of the (1,1) peak height anisotropy is the presence of a narrow trough - typically 1° wide - whenever the static magnetic field lies in a {100} plane. This feature, which corresponds to an equally sharp ridge in the anisotropy of the transverse magnetoresistivity, has escaped detection in all previous studies of the magnetoresistivity (by helicons and otherwise), and it is a consequence of the magnetic breakthrough which is required by the Ashcroft model of the Fermi surface of aluminium. The transverse magnetoresistivity oscillates (periodically in 1/B) whenever the magnetic field is parallel to a <100> direction and this feature is likewise consistent with the Ashcroft model. Other quantum oscillations have been observed superimposed on the helicon resonance and their periodicities are found to agree closely with those in the de Haas-van Alphen effect. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The effect of optical mixing of two tunable dye lasers at frequencies near the plasma frequency has been experimentally investigated in a helium plasma jet. It has been shown that the wave mixing produces longitudinal plasma oscillations at the frequency and wave vector of the mixing force. The driven waves were detected by scattering a third diagnostic light wave from their density fluctuation. The scattering signals increased to as much as seven times the signal observed when scattering from the thermal fluctuations alone. The spectrum of the spectral density function of the induced fluctuations has been measured, as well as the dependence of its amplitude on the power of the mixing light beams. These results agree well with theoretical calculations based on a simple model of the mixing effect of a single electron in the field of two electromagnetic waves. The response of the plasma to optical mixing at different frequencies has also been measured. This spectrum agrees in part with theoretical predictions, but has features not explained by the simple model. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Orientador: Edison Bittencourt / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-26T21:57:48Z (GMT). No. of bitstreams: 1 Silva_SoniaFonsecaCostae_D.pdf: 7122538 bytes, checksum: 168b9088ec0fd3c2e7dc5392747cded0 (MD5) Previous issue date: 2015 / Resumo: Compósitos ablativos são vastamente utilizados em divergentes de motores usados em veículos espaciais, em particular nos veículos em desenvolvimento no Instituto de Aeronáutica e Espaço, como por exemplo, o Veículo Lançador de Satélite. Tais divergentes podem ser produzidos por diversos processos, entre eles a bobinagem. Atualmente é empregado o processo de bobinagem paralela para a fabricação desses elementos. Porém, visando obter-se um melhor desempenho ablativo e otimização da massa para os divergentes, propõe-se uma inovação no processo de fabricação para estruturas ablativas, a bobinagem inclinada em fitas tecidas. Neste trabalho foi realizado um estudo teórico experimental da ablação em compósitos bobinados obtidos através dos dois processos de bobinagem, paralela e inclinada. Uma tocha de plasma é usada para simular as condições de operação do material em um divergente. O material utilizado como reforço do compósito foi um tecido de fibra de carbono e o polímero utilizado como matriz foi uma resina fenólica tipo resol. Nestas condições, foram avaliadas a taxa de perda de massa e as temperaturas atingidas na face exposta a tocha, tendo como parâmetro o fluxo térmico do jato de plasma. Os dados experimentais foram comparados com os resultados numéricos de uma simulação computacional. Embora não tenha sido obtida uma perfeita concordância entre os resultados numéricos e experimentais, a ordem de magnitude e o comportamento de variação dos parâmetros avaliados podem ser considerados fisicamente coerentes e dentro dos limites do modelo teórico proposto. Os resultados obtidos permitem estimar a taxa de perda de massa de acordo com o fluxo térmico e indicam um melhor desempenho ablativo das amostras obtidas por bobinagem inclinada em comparação com as amostras obtidas por bobinagem paralela / Abstract: Ablative composites are widely used in nozzles of propeller engines used in space vehicles, as the Satellite Launching Vehicle in development at Aeronautics and Space Institute, for example. Such nozzle extension can be produced by various processes, including wrapping tape. Currently is employed the parallel wrapping process to manufacture these elements. However, in order to get a better ablative performance and mass optimization for the nozzle extensions, it has been proposed an innovation in the manufacturing process for ablative structures, biased tape wrapping. In this paper is presented a theoretical study of experimental ablation in wound composite obtained by the two wrapping processes, parallel and biased tape. A plasma torch has used to simulate the operating conditions of the material in the nozzle extension. The composite has used as reinforcement a carbon fiber fabric with a resol phenolic resin matrix. Thus, it has evaluated the weight loss rate and the temperatures reached on the face to the side exposed to the torch, with the heat flux parameter of the plasma jet. The experimental data were compared with the numerical results of a computer simulation. Although not obtained a perfect agreement between the numerical and experimental results, the order of magnitude and the pattern of variation of the evaluated parameters can be considered physically consistent and within the limits of the proposed theoretical model. The results obtained allow us to estimate the mass loss rate in accordance with the thermal flow and indicate a better ablative performance of samples obtained by biased tape wrapping in comparison with the samples obtained by parallel wrapping / Doutorado / Ciencia e Tecnologia de Materiais / Doutora em Engenharia Quimica

This dissertation presents experiments that studied two gravity driven granular channel flows. The first experiment used magnetic resonance imaging to measure the density and displacement distributions of poppy seeds flowing in a rough walled channel. Time-averaged measurements of normalized velocity and density showed little flow speed dependence. Instantaneous measurements, however, showed marked velocity dependence in the displacement distributions. There was evidence of aperiodic starting and stopping at lower flow speeds and the onset of density waves on a continuous flow at higher speeds. The second experiment measured forces in all three spatial directions at the boundary of a flow of steel balls. The relationship between the normal and the tangential forces were examined statistically and compared to the Coulomb friction model. For both large and small forces, the tangential and normal forces are unrelated, as there appears to be a strong tendency for the tangential force to maintain a value that will bear the weight the weight of the particles in flow.

The means by which magnetic reconnection in Earth's space environment is observed is limited by current instrument technology and timing of satellite orbits. Imaging capabilities from a spacecraft platform are still developing, and in-situ measurements are confined to the spacecraft's orbit. The goal of this dissertation is to provide and apply methods by which the spatial extent of magnetic reconnection at Earth's magnetopause can be quantified. An accepted single value, or range of spatial extents of magnetopause reconnection has eluded the scientific community for over half a century. This dissertation provides two methods by which the spatial extent can be sampled. First, with the development of a CubeSat, the Cusp Plasma Imaging Detector (CuPID). CuPID is built with a wide field-of-view soft X-ray telescope to image the photons resulting from solar wind charge exchange between atmospheric neutrals and high charge-state solar wind ions. During magnetic reconnection at the magnetopause, solar wind ions are routed along field lines to Earth's cusps in the polar regions. In the magnetospheric cusps, these solar wind ions can penetrate deeper into Earth's neutral atmosphere, producing an observable signal for a low Earth orbiting satellite. The design of the CuPID mission and the calibrations of CuPID's instruments are presented. CuPID was launched in September 2021, but did not respond to commanding from the ground. Efforts to modify and improve the ground station led to the discovery of a probable root cause of failure with CuPID's flight radio. A second method of observing magnetic reconnection utilizes in-situ measurements of plasma populations and magnetic fields. The THEMIS mission, orbiting five satellites continuously since 2007, traverse the magnetopause nearly every orbit when their orbital apogee is on the dayside. When two spacecraft cross the magnetopause simultaneously and both observe features of magnetic reconnection, the spatial extent of reconnection is constrained by their spacing. Using statistics from 174 events of spacecraft conjunctions at the magnetopause, the spatial extent of reconnection as observed by THEMIS is on average 3,148 km. This study also investigates the processes by which magnetic reconnection is constrained, including plasma beta gradient drifts and position on the magnetopause flanks.

In this research we study the mixing of viscous fluids in a model flow, the eccentric cylinder system. The flow between eccentric rotating cylinders is used because an analytic expression for the stream function exists and we have fabricated an apparatus to experimentally generate the flow. We use the flow to determine the extent to which several computational methods are able to predict the experimental mixing in the flow. We have found that Poincare sections give a good indication of the maximum extent of mixing in the experiments but they give no information on the rate of mixing. The locations of elliptic periodic points give an indication of where 'islands' of regular behavior will occur in the flow. The manifolds of the hyperbolic periodic point with the largest eigenvalue give a template of the striation pattern which forms in the experiments. Finally, stretching plots appear to match the experiments quite well. We have found that co-rotation of the cylinders leads to mixing over a larger region of the flow domain than the equivalent counter-rotating motion of the cylinders. Driving the cylinders with different waveforms appears to produce little or no difference in the mixing. The Melnikov method has been adapted to adjust the waveforms such that the resultant mixing is in even closer agreement. In addition, we have determined that the points which stretch the most start on the stable manifold of a hyperbolic periodic point and end up on the unstable manifold. This results in the stretching plots assuming the shape of the manifolds and consequently matching the striation patterns of the experiments. Finally, we have determined that the methods of analysis presented here can be applied to flows where only a discretized representation of the velocity field exists. This means that our methods of analysis will be effective even when the flow field must be determined numerically.

The equilibrium statistical behavior of phase flows on surfaces of complicated topology is studied. Both classical tools developed in the theory of Riemann surfaces and numerical methods associated with discrete mathematics (graph theory) are applied to the characterization of the equilibrium statistical behavior of systems with U(1) symmetry on two-dimensional manifolds. The relation between a surface's topology and physical parameters such as the superfluid density, vortex core shape and boundary effects is investigated. The effect of quantization is traced through the characterization of states via the Hodge decomposition and in the partition function. It is shown that for surfaces of an appropriate shape a new type of Kosterlitz-Thouless transition is possible. This situation is novel because quantized vortices are required only for ergodicity and the disordering of the superfluid/normal phase transition is by fluctuations in the nonsingular harmonic flows.

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