Shock Structure in a Partially Ionized Gas

Abstract

The structure of a steady plane shock in a partially ionized gas is investigated using the Navier-Stokes equations for the atom, electron, and ion fluids. Across the shock, quasi-neutrality and frozen ionization is assumed. For all degrees of ionization there is shown to be a broad thermal layer of elevated electron temperature ahead of the shock front and a precursor and imbedded axial electric field induced by the charge separation. Because of the large atom-ion charge exchange cross section, ion slip is small for less than 30% ionization. In a weakly ionized plasma, the atom flow is unaffected by the ionized particles and the structure consists of an ordinary atom shock imbedded in the thermal layer. For substantial ionization, the heavy particles are compressed and heated in the thermal layer and in the shock the ion and atom temperatures overshoot their downstream values. The induced electric fields increase with degree of ionization and free stream Mach number while the shock thickness decreases. A measurement in partially ionized hydrogen of potential variation in a strong shock gives a potential rise across the imbedded shock and thickness in good agreement with the calculated values.