Modeling the propagation of a shock wave through a glow discharge

Several well-known analytical solutions of the equations of gasdynamics and magnetogasdynamics were used to study the relative importance of exothermi c reactions, axial temperature variation, and the magnetic field in the glo w discharge tube experiments of Ganguly et al. (Physics Letters A, Vol. 230 , 1997, pp. 218-222). In these experiments a spark was generated at one end of a tube of low-pressure argon gas, and the resulting shock pulse was all owed to propagate through a glow discharge. With the presence of the weakly ionized, nonequilibrium plasma, an acceleration and weakening of the shock pulse were observed, along with an apparent splitting of the shock. Of the three mechanisms addressed here thermal nonuniformity appears to have the most influence on the experimental results. A detonation model fan probably be ruled out for two reasons. First, insufficient energy is available from electron-ion recombination reactions to drive the detonation. Second, the detonation model predicts an increase in shock density ratio with increasin g heat release, in contrast to the apparent drop seen in the experiments. I n a similar manner an ideal magnetohydrodynamic shock model can probably be ruled out for lack of adequate electrical conductivity and of a sufficient ly strong magnetic field. This conclusion does not, however, exclude other electromagnetic phenomena, and the issue of the apparent shock splitting ha s not been addressed here. A combination of careful temperature measurement s and numerical simulations is required to determine whether the experiment al observations can be explained completely by thermal effects or physics i nherent to the plasma are significant in these experiments.