Ion Transport in a Plasma Vortex
Alan P. Matthews
Department of Physics,
University of Natal, Durban, South Africa
Roland Grappin, Andre Mangeney, Jaques Leorat
Observatory of Paris
Meudon 92190, France
This is a simulation study of a vortex in a collisionless plasma. Ion kinetic behavior is modeled by resolving ionic time and space scales and treating ions as particles, whereas electrons are modeled as a background, neutralizing fluid (a "hybrid" model). The vortex is a non-linear structure not initially in equilibrium, and it evolves to form steep gradients which trigger waves. These simulations have been compared with the results from fluid (MHD) simulations, with and without the dispersive Hall term. The large-scale behavior of the vortex is produced in MHD simulations, but the waves are only generated when the Hall term is included. The hybrid (ion particle) simulations produce similar results in the fluid and field quantities to the fluid simulations, except that they do not require explicit dissipative terms in governing equations. The fluid simulations, however, are unstable without some ad-hoc viscosity and resistivity. Therefore the hybrid simulations must be stablised by the ion kinetic behavior. Furthermore, the hybrid simulations permit departures from Maxwellian ion velocity distributions. Bimaxwellian distributions develop in the vortex, as well as some apparent heating. This heating seems to be anamalous due to the mixing of ion populations along a flux tube. Ions stream freely along flux tubes on the scale of the vortex, whereas a fluid model assumes that ions are localized at least on the scale of a grid cell. The effects of this streaming on the global properties of the vortex will be examined.