Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 166-171).

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis--Wisconsin. / Vita. Includes bibliographical references.

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This is a study of the plasma diffusion processes relevant to the physical nature of the Io plasma torus at Jupiter. A knowledge of the diffusion processes involved in the Io plasma torus is essential to an understanding of the spatial structure and energetics of the torus. The only published theory of Io torus plasma diffusion, centrifugally driven flux tube interchange instability, is based on turbulent plasma interchange instability. We have examined physical properties that lead us to conclude that flux tube interchange diffusion is not a valid mechanism in the plasma torus. The collisional nature of the hot torus plasma is seen through its observed EUV emissions which dominate the energy loss from the system. Further, the torus plasma parameters fall in the range of values satisfying the criteria for the use of collisional transport theory to derive a collisional diffusion coefficient. The collisional nature of the torus plasma is characterized in the long mean free path regime where classical transport theory breaks down. We study the Chapman-Enskog method of calculating the plasma diffusion coefficient from a solution of the Boltzmann equation. Simplifying approximations of a fully ionized plasma dominated by Coulomb elastic charged particle collisions are made to derive an ad hoc non-classical diffusion coefficient which results in slow differential diffusion rates for the various sulfur and oxygen ions in the plasma torus. The radial spatial structure and energetics of the plasma torus is modeled by employing the collisional diffusion coefficient in a computer model calculation of collisional ionization-diffusive equilibrium and energy branching. The computer model employs the known significant plasma reactions involving the torus sulfur and oxygen species, utilizing the most recently available atomic parameters. In view of the failure of Neutral Cloud Theory to adequately power the copious amounts of UV radiation emitted by the Io plasma torus, we employed the radial plasma model to investigate this "energy crisis." Toward this end, we investigate the application to our plasma model of a proposed heterogeneous source of energetic electrons and a proposal of inward diffusing energetic outer-magnetospheric OII and SII ions as ad hoc heat inputs to the plasma torus electrons, in order to maintain a steady state energy balance.

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Thesis (Ph. D.)--University of Texas at Austin, 2004. / Supervisors: Ronald V. Bravenec and Kenneth W. Gentle. Vita. Includes bibliographical references.

The suppression of turbulent transport is a key requirement for enabling nuclear fusion to become a viable energy source. One possible route to achieving this suppression is through toroidal flow shear. We investigate the effect that flow shear has on the structure of turbulence by analysing data from both measurements of the fluctuating intensity field using the Beam-Emission-Spectroscopy (BES) diagnostic on the spherical tokamak MAST, as well as from numerical simulations of the fluctuating density field in MAST. We develop a procedure to map from the correlation parameters of the intensity field to the correlation parameters of the density field. This procedure is illustrated using the MAST BES system and the validity of the underlying assumptions is tested on fluctuating density fields generated by direct numerical simulations using the gyrokinetic code GS2. By using this procedure, we demonstrate how, in experiment, the flow shear associated with the differential toroidal rotation of tokamak plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by the up-down symmetry of the magnetic equilibrium. Indeed, in both experimental BES measurements and gyrokinetic simulations, this symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself as a tilt of the spatial correlation function and a finite skew in the distribution of the fluctuating intensity (density) field. The tilt is a statistical expression of the "shearing" of the turbulent structures by the mean flow. The skewness of the distribution is related to the emergence of long-lived density structures in sheared, near-marginal plasma turbulence. The extent to which these effects are pronounced is argued (with the aid of the simulations) to depend on the distance from the non- linear stability threshold. Away from the threshold, the symmetry is effectively restored.