Experiments and simulations of DC and pulsed discharges in air plasmas

Experiments were conducted with atmospheric air plasmas at temperatures around 2000 K in order to increase the electron number density to approximately 10¹³ cm^-3 by means of an applied DC discharge and an electric pulse in parallel to the DC discharge. The DC discharge produces a stable region of elevated electron number density, in agreement with two-temperature kinetics calculations. In the pulsed experiments at the end of the 10 ns pulse, the ionization level was measured to be about 10¹³ electrons/cm³. Following the pulse, the electron number density decreased to 10¹²cm^-3 in approximately 12μs, in good agreement with the chemical kinetics model. This result suggests that elevated electron number densities of the order of 10¹³cm^-3 can be maintained in low temperature air plasmas by means of repetitively pulsed discharges. In this paper, we present results of the DC and pulsed experiments, as well as two-dimensional CFD simulations of the DC experiments. The computational model uses the Stanford two-temperature chemical kinetics model for the plasma, as well as finite-rate models for vibration-electronic energy relaxation and electron translational energy relaxation. The computational results are in good agreement with the measured electron concentration, temperatures, and cathode fall.