Self-Organization and Heating by Inward Diffusion in Magnetospheric Plasmas

TL;DR

This paper explains how inward diffusion in magnetospheric plasmas creates localized plasma clumps and preferential perpendicular heating, using a canonical formalism and statistical mechanics, supported by numerical simulations.

Contribution

It develops a canonical formalism for guiding center dynamics and constructs a constrained statistical mechanics framework for inward diffusion in dipole magnetic fields.

Findings

Inward diffusion creates localized plasma density gradients.

Particles experience preferential perpendicular heating during inward diffusion.

Numerical simulations confirm the theoretical predictions.

Abstract

Through the process of inward diffusion, a strongly localized clump of plasma is created in a magnetosphere. The creation of the density gradient, instead of the usual flattening by a diffusion process, can be explained by the topological constraints given by the adiabatic invariants of magnetized particles. After developing a canonical formalism for the standard guiding center dynamics in a dipole magnetic field, we complete our attempt to build a statistical mechanics on a constrained phase space by discussing the construction principles of the associated diffusion operator. We then investigate the heating mechanism associated with inward diffusion: as particles move toward regions of higher magnetic field, they experience preferential heating of the perpendicular (with respect to the magnetic field) temperature in order to preserve the magnetic moment. A relationship between conservation of bounce action and temperature isotropy emerged. We further show that this behavior is scaled by the diffusion parameter of the Fokker-Planck equation. These results are confirmed by numerical simulations.