Plasma Stability of Electric Discharges in Molecular Gases

The results of an analytical treatment of the local low-frequency stability of weakly ionized molecular-gas mixtures consisting of a diatomic molecular species and an atomic diluent are presented. Plasma conditions typical of high-power electric-discharge-laser technology are emphasized. The calculations indicate that small-amplitude fluctuations present within these discharges excite several different wave modes. These have been identified as a space-charge relaxation mode, an electron thermal mode, an ionization mode, a negative-ion-production mode, an electronically-excited-species-production mode, a sound mode, a vibrational-energy relaxation mode, a heavy-particle thermal mode, and a vorticity mode. The stability of these modes is treated in detail with particular emphasis placed on illustrating the influence on stability of charged-particle kinetics, energy transfer, and transport processes. The influence of auxiliary ionization and aerodynamic techniques is also considered.