Plasma non-equilibrium of the DC normal glow discharges in atmospheric pressure atomic and molecular gases

Electrical and spectroscopic results of comprehensive investigations of atmospheric pressure glow discharges in helium, argon, nitrogen and air in a large current range are presented. Our attention in these investigations is mainly focused on the characterization of positive column plasmas at discharge gap of 10 mm. It was shown that helium, nitrogen and air positive columns transform from diffuse to constricted mode when discharge current increases. In argon discharge, it is constricted in the whole range of investigated currents. Reduced electric field, gas temperature, average electron energy and electron concentration were determined. The positive column plasmas of all the atmospheric pressure glow discharges studied are non-equilibrium and weakly ionized. Plasma non-equilibrium degree in atomic gases of helium and argon is essentially higher than in molecular nitrogen and air. For all gases, plasma non-equilibrium degree in a positive column decreases with discharge current increase