The MHD Plasma Flow Near the Heliopause Stagnation Region with A View On Kinetic Consistency

Most of the representative space plasma systems in our cosmic environment, - outside of stellar interiors, - like heliospheric, interstellar, or intergalactic plasmas etc., are collision-free or, at least, only weakly collision-determined systems. Nevertheless, these plasmas consist of at least two very different particle species, namely ions and electrons, i.e. particles with very disparate masses and opposite electric charges. If in these systems concerted fluid motions are arranged by electro-magnetic or gravitational forces or by inner forces like pressure gradients, then it must be asked how this combined electron-ion system finds its common internal dynamics. In most text book literature this problem is treated by considering the plasma as a mono-fluid system in which the massive protons and the nearly massless electrons are electrically closely bound together and move as an electrically neutral couple with an identical bulk velocity. Under these conditions the well-known Bernoulli law is derived for the standard MHD. If the electron pressure, however, does compete with the energy density of the ion bulk motion, then a two-fluid situation occurs, and the resulting bulk motion of the charge-neutral plasma needs to be determined on the basis of the kinetic conditions of the two different plasma fluids. In the following we shall exactly study this specific situation.