This paper is concerned with one-dimensional and time-dependent multifluid
plasma models derived from multifluid MHD equations. In order to reduce the
number of equations to be solved, the impurities are described in the framework
of the average ion approach without restricting the impurity densities to be small
compared with the hydrogen plasma density. Equalizing the plasma temperatures
and adopting the condition of quasineutrality, we arrive at a three-fluid description
of a current-carrying plasma, and analyse the ability of the self-consistent system of
model equations thus obtained to support stationary solutions in a moving frame.
This system is reduced to a currentless plasma description assuming at first different
flow velocities of the particles and then a currentless, streaming plasma where
all particles move with the same velocity. Introducing Lagrangian coordinates and
adopting an equation of state, a single reaction–diffusion equation (RDE) for the
temperature is obtained. The impurity density, which affects the radiation loss term
and the heat conduction coefficient of the RDE, has to be calculated as a function
of the temperature by solving additionally a first-order differential equation. This
is demonstrated for carbon and high-Z impurities.
Asymmetric and moving-frame approaches to MHD equations
