Removal of the heavily damped mode from the equations of a partially ionized plasma

The possibility of removing the heavily damped fast thermal mode from the equations describing a partially ionized plasma is discussed. This mode is removed when it is assumed that the electron density and temperature are in Saha equilibrium, although the resulting solutions are only accurate at high temperatures. It is shown that the fast thermal mode can also be removed by neglecting the temperature relaxation term in the electron energy equation; and that the approximate solutions are accurate over a wide range of electron temperatures.