Theory of Nonlinear Diffusion of Plasma Across a Magnetic Field. II. Application to Diffusion Studies in a Toroidal Multipole.

摘要

The authors study a model for cross-field plasma diffusion which describes the observed density profile shape and decay in the Wisconsin levitated octupole in certain regimes. The boundary conditions of the model are zero density at the two plasma edges. The authors have shown that the observed profile, which is peaked off the separatrix and retains a constant shape as the profile decays, has the spatial and temporal dependences of the separable solution to the diffusion equation. Furthermore, according to a stability analysis of the model, perturbations decay at least four times as fast as the final stable profile; thus, the observed rapid evolution toward a stable shape is explained. The authors conclude that the model is useful for determining diffusion coefficient magnitude and scaling with density once the density profiles are known.