LXXV. Collisional effects and the conduction current in an ionized gas

Abstract A first approximation to the transport equation for the conduction current in a binary ionized gas is derived by the iterative methods of Enskog and Chapman. The collision-integrals that arise are evaluated in terms of the current density, as suggested by the results of 'free-path' theory. It is found that the collisional damping factor is a weighted mean of the electron and ion collision frequencies instead of the electron collision frequency. In practice the difference amounts to a factor 4/3, as predicted in an earlier paper. When applied to static fields the equation yields Chapman and Cowling's formulae without further calculation. Corresponding approximations are made to the equations of conservation, motion and thermal energy. With Maxwell's equations these provide a reliable set for the investigation of intera(tions between an ionized gas in motion and the associated radiation field. The results are applicable to the solar atmosphere and the H II regions of interstellar space. With slight modifications they are also made applicable to a slightly ionized gas such as the H I regions and the lower ionosphere.