PHENOMENOLOGICAL ANALYSIS OF SHOCK-WAVE PROPAGATION IN WEAKLY IONIZEDPLASMAS

Shock propagation into weakly ionized gases shows several features dif fering markedly from conventional, nonionized-gas shock structure. Phe nomenological analysis of general macroscopic features of the previous ly observed plasma shock effects allows only two possible interpretati ons: existence of an energy (momentum) flux toward the wave precursor or volumetric energy release (exothermic phase transition! in the upst ream portion of the wave !precursor) followed by reverse transition in the downstream portion of the wave. It is shown that known microscopi c mechanisms are not capable of producing such a flux or energy releas e: Typical processes involving electrons, ions, and excited species do not couple strongly to neutral atoms and molecules, and there is not enough energy stored in these species because of the low ionization fr action. The theoretical basis for phase transitions in low-density, we akly ionized plasmas also is unknown. Analysis of the steady two-wave system created by either of the two effects raises a question as to wh ether the observed plasma shocks are stable objects. Another question is whether there exists phase transition within the plasma shock. It a lso remains unclear to what extent two-dimensional thermal inhomogenei ty effects contribute to the observed phenomena. Answering these Funda mental questions requires additional experimental studies of the probl em.