Two-fluid simulations of the reversed-field pinch
R. A. Nebel · University of North Texas Digital Library (University of North Texas) · 1990
Two fluid and transport effects have recently been incorporated into the 3-D MHD code (Debs) originally developed by Schnack and coworkers. These include the Hall effect, diamagnetic drift effects, Braginskii viscosity and anisotropic thermal conduction. Incorporation of these effects required the development of new semi-implicit operators in order to provide numerical stability. Both anisotropic thermal conduction and parallel viscosity make the equations extremely stiff and require some care in formulation in order to avoid matrix conditioning problems. In general, these new concerns favor using simple isotropic operators (such as {nabla}{sup 2}) over the less dispersive but exact anisotropic semi-implicit operators. These numerical formulations will be discussed in detail. Accuracy and poisoning'' checks also will be presented. Results indicate that a number of new phenomena are present in these extended equations. For instance, the dynamo effect'' is seen to emerge from the Hall terms rather than the MHD terms if the viscosity is large. The observed relaxation is also much more robust than its MHD counterpart. Resistive wall instabilities are seen to lock nonlinearly to the wall if the edge viscosity is large but not to lock if the viscosity is small. Similarly, resistive g-modes are also very sensitive to the amount of viscosity present. The significant factor in all of these phenomena appears to be the parallel viscosity. 22 refs., 9 figs.