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Analysis of classical transport equations for the Tokamak edge plasma

Description: The classical fluid transport equations for a magnet-plasma as given, for example, by Braginskii [1], are complicated in their most general form. Here we obtain the simplest reduced set which contains the essential physics of the tokamak edge problem in slab geometry by systematically applying a parameter ordering and making use of specific symmetries. An important ingredient is a consistent set of boundary conditions as described elsewhere [2]. This model clearly resolves some important issues concerning diamagnetic drifts, high parallel viscosity, and the ambipolarity constraint. The final equations can also serve as a model for understanding the structure of the equations in the presence of anomalous transport terms arising from fluctuations. In fact, Braginskii-like equations are the basis of a number of scrape-off layer (SOL) transport codes [3]. However, all of these codes contain ad hoc radial diffusion terms and often neglect some classical terms, both of which make the self-consistency of the models questionable. Braginskii's equations [1] have been derived from the first principles via the kinetic equations and, thereby, contain such ''built-in'' features as the symmetry of kinetic coefficients, and automatic quasineutrality of a cross-field diffusion in a system with toroidal symmetry such as a tokamak. Our model thus maintains these properties.
Date: September 29, 1997
Creator: Rognlien, T. D., LLNL
Partner: UNT Libraries Government Documents Department

Influence of E{times}B and {nabla}{ital B} deift terms in 2-D edge/SOL transport simulations

Description: Classical particle drifts across the magnetic field can play an important role in tokamak edge-plasma transport. The relative influence of these terms is studied for self-consistent simulations by including them, together with anomalous diffusion transport, in a 2-D fluid model of edge-plasma transport for the DIII-D tokamak geometry. The drifts cause asymmetries in the plasma equilibrium which depend on the direction of the magnetic field, B. The basic results can be understood by dividing the drifts into three categories: diamagnetic, E x B, and {nabla}B. The dominant effect near the divertor plates is from the E x B drifts, while the weaker {nabla}B drifts cause an increase in the magnitude of the radial electric field inside the magnetic separatrix. The diamagnetic terms, defined as divergence free, do not contribute to transport.
Date: May 15, 1998
Creator: Rognlien, T. D., LLNL
Partner: UNT Libraries Government Documents Department