Shock wave propagation through glow discharge plasmas: Evidence of thermal mechanism of shock dispersion

The paper examines, experimentally and computationally, propagation of shock waves in weakly ionized plasmas. Spark-generated shocks were studied in glow discharges in argon and argon-nitrogen mixtures. UV Filtered Rayleigh Scattering was used to measure radial profiles of gas temperature, and laser Schlieren (laser beam deflection) method was used to measure shock arrival times and axial density gradients across the shock. Highly accurate inviscid axisymmetric CFD computations were run and compared with the experiments. Comparison of experimental and computational results show that experimentally observed changes in shock structure and velocity in weakly ionized gases are explained by conventional gas dynamics, with thermal effects and non-one-dimensionality (transverse gradients, shock curvature, etc.) playing a critical role. A direct experimental proof of the thermal mechanism was provided by pulsing a glow discharge. With several hundred microseconds time delay between starting the discharge and shock launch, electric current, field, and the discharge luminosity reach their steady-state values, while the temperature is still cold. In this regime, laser Schlieren signals are virtually identical to those without the discharge, differing dramatically from the signals in discharges with fully established temperature profiles. 2000 by Princeton University.