A unified, linear theory is formulated for MHD waves at low magnetic Reynolds number, propagating transverse to the magnetic field in a weakly ionized, radiating plasma. The set of equations obtained from a two-fluid model yields a fifth-order dispersion relation whose roots correspond to four waves: magnetoacoustic (a paired wave), thermal, electrothermal, and "ionization-rate." To bring out the physics of each of these waves, simplifying assumptions are made, and "simple" analytical wave solutions are found. By taking advantage of the wide separation of the roots in the complex plane, "distinct" wave solutions are obtained in which many limitations of the "simple" wave solutions are absent and which are in excellent agreement with the roots of the full dispersion relation, obtained numerically. Both thermal and magnetoacoustic waves are shown to require a two-fluid model for proper description. In particular, the latter mode requires the inclusion of the rate of change of electron enthalpy for wavelengths < 0.1 m, at typical MHD generator conditions. The electrothermal wave instability region is much larger than previously thought, whereas the "ionization rate wave" is always stable.
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