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Pure Appl. Chem., 2002, Vol. 74, No. 3, pp. 337-347

Nonequilibrium discharges in air and nitrogen plasmas at atmospheric pressure

Charles H. Kruger, Christophe O. Laux, Lan Yu, Denis M. Packan and Laurent Pierrot

High Temperature Gas Dynamics Laboratory, Mechanical Engineering Department, Stanford University, Stanford, CA 94305, USA

Abstract: Diffuse glow discharges were produced in low temperature (<2000 K) atmospheric pressure air and nitrogen plasmas with electron number densities in excess of 1012 cm­3, more than six orders of magnitude higher than in thermally heated air at 2000 K. The measured discharge characteristics compare well with the predictions of a two-temperature kinetic model. Experimental and modeling results show that the steady-state electron number density exhibits an S-shaped dependence on the electron temperature, a behavior resulting from competition between ionization and charge-transfer reactions. Non-Maxwellian effects are shown to be unimportant for the prediction of steady-state electron number densities. The power requirements of DC discharges at atmospheric pressure can be reduced by several orders of magnitude using short repetitive high-voltage pulses. Between consecutive pulses, the plasma is sustained by the finite rate of electron recombination. Repetitive discharges with a 100-kHz, 12-kV, 10-ns pulse generator were demonstrated to produce over 1012 electrons/cm3 with an average power of 12 W/cm3, 250 times smaller than a DC discharge at 1012 cm­3.