Extended hydrodynamical models for plasmas

Abstract

We propose an extended hydrodynamical model for plasmas, based on the moments of the electron distribution function which satisfies the Fokker–Planck–Landau (FPL) transport equation. The equations for the moments can be obtained by multiplying the FPL equation by the corresponding weight functions and integrating over the velocity space. The moments are decomposed in their convective and non–convective parts and closure relations for the fluxes and production terms can be obtained by using the maximum entropy distribution function, which depends on Lagrangian multipliers. These latter can be expressed in terms of the state variables by imposing the constraints that the maximum entropy distribution function reproduces the moments chosen as state variables. In particular, we will concentrate on the 13-moment system. As a first application, we treat the case of the relaxation towards equilibrium of a homogeneous plasma with a temperature anisotropy, showing that the results are in good agreement with those obtained by means of the Kogan solution of the kinetic equation.