Magnetic presheath in a weakly turbulent multicomponent plasma

Abstract

A fluid model of the magnetic presheath in a weakly turbulent multicomponent plasma consisting of electrons and several positive ion components is presented. Turbulent particle source terms in the continuity equations and turbulent momentum source terms in the momentum balance equations for the ion components are derived from basic principles [Plasma Phys. Controlled Fusion 47, 685 (2005)], i.e., by means of the ensemble averaging procedure from the statistical theory of plasma turbulence. Then the unknown correlations between the fluctuating quantities occurring in the turbulent source terms derived are replaced with phenomenological expressions based on analogy with classical transport. The remaining correlation terms in the momentum balance equations, which are responsible for explicit coupling of the equations for different ion components, reduce to the corresponding classical terms when the turbulent transport corrections are negligible (i.e., for “quiescent” plasmas). Under certain conditions regarding the nature of the boundary plasma turbulence, the analysis of the planar magnetic presheath performed in this study yields results for the ion component fluid velocities and particle flux densities at the magnetic presheath entrance that are directly applicable to the boundary conditions of multifluid plasma transport and turbulence codes. A fluid formulation of the Bohm criterion, valid for weakly turbulent multicomponent plasmas as treated in this study, is also derived.