Charged particle transport in turbulent magnetic fields: The perpendicular diffusion coefficient

Abstract

The diffusion of charged particles in a static turbulent magnetic field, which is superimposed on a constant magnetic fieldB ₀ k, is considered. Previous calculations of the particle flux in a direction perpendicular tok have related the fluxS _⊥ to the particle number densityf byS _⊥ = − κ_⊥(▽f)_⊥ where κ_⊥ is found from the power spectrum of the turbulent magnetic field. It is shown that this formula is inconsistent with the notion, developed by Jokipii and Parker (1969), that the perpendicular particle flux primarily arises because of random-walking of magnetic field lines across the directionk. For a simple example of a turbulent magnetic field it is shown that the above expression forS _⊥ is incorrect; the particle fluxS _⊥ is recalculated and a new relationship betweenS _⊥ andf is found. This new expression forS _⊥ is shown to be consistent with particle diffusion across the directionk being due to random-walking of the magnetic field lines.