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Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Neutral particles play an important role on the performance of tokamak plasmas. In this dissertation, the original TEP methodology has been extended to take into account linearly (DP_1) and quadratically (DP_2) anisotropic distributions of angular fluxes for calculations of transmission probabilities. Three approaches, subdivision of optically thick regions, expansion of collision sources and the diffusion approximation, have been developed and implemented to correct effects of the preferential probability of collided neutrals escaping back across the incident surface. Solving the diffusion equation via the finite element method has been shown to be the most computationally efficient and accurate for a broader range of D/l by comparisons with Monte Carlo simulations. The average neutral energy (ANE) approximation has been developed and implemented into the GTNEUT code. The average neutral energy approximation has been demonstrated to be more accurate than the original local ion temperature (LIT) approximation for optically thin regions. The simulations of the upgraded GTNEUT code excellently agree with the DEGAS predictions in DIII-D L-mode and H-mode discharges, and the results of both the codes are in a good agreement with the experimental measurements.

The inner magnetosphere modeling is an important component of the magnetosphere simulation frameworks with significant implications for space weather and a. principle methodology to understand the magnetospheric response to changes in the solar wind. The thesis shows our efforts in constructing and validating the contemporary Rice Convection Model (RCM) code and its interface as a next-generation code to predict electric fields, field-aligned currents, and energetic particle fluxes in the inner magnetosphere and subauroral ionosphere during geomagnetic disturbed times. The RCM was used to simulate the geomagnetic storms with fixed boundary conditions of time-dependent Tsyganenko-Mukai boundary conditions. This work shows the results of two extremely- strong storm events with significant interchange motion. The ring current injection predicted by the RCM is shown to be overestimated, consistent with the previous results of overestimating particle fluxes by the RCM. This effect is magnified here since the southward component of interplanetary magnetic field is very strong reaching about 50 nT. Time-dependent Borovsky's boundary condition is implemented and used to alleviate the huge pressure and get better tendency of ring current energy calculated by the Dessler-Parker-Sckopke relation. This work also describes a new module of generalized Knight's relation to compute the parallel potential drops from the calculated field-aligned currents through Vasyliunas equation. It gives different ionospheric conductance and plasma drift signatures particularly around the midnight. The inclusion of parallel electric fields will replace the treatments of energy flux in the substorm simulations since that the Hardy normalization cannot perform the desired function during the substorm expansion phase and the energy flux floor gives arbitrary enhanced the precipitating energy flux and ionospheric conductances at high latitude especially for the westward clectrojet around the midnight. Since the original Knight's relation gives too large field-aligned potential drop, the modified Knight's relation is applied and implemented successfully into the RCM. Therefore, the RCM is capable of real time event simulation including strong geomagnetic storms and magnetospheric substorms, although full validation of model predictions with typical observations remains to be done.