Friction Force Densities

Our model expressions for the friction force densities, and , are taken from the moment-based analysis of Hirschman & Sigmar [24,34]. The ion friction force densities are written

where The electron friction force densities take the form where Note that , , and , for , ensuring that which is a statement of collisional momentum conservation [18]. Note, further, that , , and , for , which ensures that and are invariant under a Galilean transformation of the coordinate system.