PARTICLE DENSITIES AND NONEQUILIBRIUM IN A LOW-PRESSURE ARGON PLASMA-JET

Plasma diagnostic techniques have been employed to determine particle densities and temperatures in a low-pressure argon plasma jet generate d by a cascade arc. These measurements allow characterization of the e xtent to which the plasma jet deviates from thermodynamic equilibrium and provide a basis for predicting how reactive gases will interact wi th the excited and ionized species in the plasma jet. It was found tha t the distribution of atomic states in the plasma jet is not adequatel y described by either local thermodynamic equilibrium (LTE) or partial local thermodynamic equilibrium (pLTE), and the jet was optically thi ck for 3p-->4s transitions across the jet radius. Excited argon neutra ls outnumber ions by a large ratio, and dominate subsequent dissociati on/excitation phenomena. The rate of methane destruction in the plasma jet shows that estimates for particle densities, temperature, and jet velocity are self-consistent.