Double Electric Layer in the Stationary Shock Wave Structures of a Supersonic Flow

Understanding the interaction between a weakly ionized gas and a shock wave is important for detailed knowledge of the conditions of planetary atmospheric entry. This interaction can manifest itself in the form of a localized increase of electron temperature, plasma induced shock dispersion and acceleration, optical emission enhancement, or double electric layers. In our work, a microwave discharge was combined with the flow tube to sustain a supersonic flow of ionized gas. Stationary shocks formed in front of a spherical model. Argon and Ar/H2 (95/5%) mixture were used as test gases. Excited state populations of the argon (4p-4s) spectral lines were measured across the stationary shock by employing absolute emission spectroscopy. We compared measured intensity in the subsonic and the supersonic regions of the flow and observed dispersion effects in the form of a double-peak distribution. Kinetic modeling of the discharge was performed and the associated transport parameters and rate coefficients were calculated.