The modelling of a He-H2O mixture gas positive column plasma

A numerical modelling of small concentrations of water vapour in a glow discharge positive column plasma in Helium gas was conducted. The coupled density equations involving the ions (He+, He2+), the water vapour ions (H+(H2O)sub(n = 1,2,3), H2O+, OH+, H+) and metastable atoms (He*) were solved to determine the electron temperatures and the number densities of both the charged and metastable particles. The results show that (1) the major ions producted in the plasma are H2O+ and H3O+ at a gas pressure p >= 1 Torr; when partial pressure of water p(H2O) >= 10-4 Torr; (2) t he electron temperature is affected by small concentrations of water vapour due to Penning ionization by metastables; and to the dissociative recombination of H+(H2O)sub(n) and H2O+; (3) the number density of the metastables decreases rapidly due to Penning ionization, even if there is a small amount of water vapour in the discharge system. (author)