Wave—mean-field interaction in two-fluid plasmas near the magnetohydrodynamic slow manifold*

The magnetohydrodynamic (MHD) model of a plasma omits a variety of important physical effects, e.g., the nonlinear effect of waves oscillating on timescales much shorter than the characteristic MHD timescales. Starting from the two-fluid—Maxwell model, we construct an asymptotic theory of high-frequency waves interacting with MHD mean fields. The resulting asymptotic model is a generalization of MHD that incorporates (a) the ponderomotive forcing of nominally MHD plasma motions by the high-frequency wave fields and (b) the self-consistent transfer of energy and momentum between the wave-like and MHD-like dynamics. Consequences of the theory are discussed.