Shock wave propagation and dispersion in glow discharge plasmas

Spark-generated shock waves were studied in glow discharges in argon and ar gon-nitrogen mixtures. Ultraviolet filtered Rayleigh scattering was used to measure radial profiles of gas temperature, and the laser schlieren method was used to measure shock arrival times and axial density gradients. Time accurate, inviscid, axisymmetric fluid dynamics computations were run and r esults compared with the experiments. Our simulation show that changes in s hock structure and velocity in weakly ionized gases are explained by classi cal gas dynamics, with the critical role of thermal and multi-dimensional e ffects (transverse gradients, shock curvature, etc.). A direct proof of the thermal mechanism was obtained by pulsing the discharge. With a sub-millis econd delay between starting the discharge and shock launch, plasma paramet ers reach their steady-state values, but the temperature is still low, lase r schlieren signals are virtually identical to those without the discharge, differing dramatically from the signals in discharges with fully establish ed temperature profiles. (C) 2001 American Institute of Physics.