Nonequilibrium discharges in air and nitrogen plasmas at atmospheric pressure

Diffuse glow discharges were produced in low temperature (<2000 K) atmospheric pressure air and nitrogen plasmas with electron number densities in excess of 10(12) cm(-3), 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 10(12) electrons/cm(3) with an average power of 12 W/cm(3), 250 times smaller than a DC discharge at 10(12) cm(-1).