Active stabilization of low-current arc discharges in atmospheric-pressure air

Low-current (similar to 250 mA), high-voltage (similar to 700 V), dc discharges are observed to operate in air at atmospheric pressure when a closed loop is included for current regulation on the power supply. A dynamic process might control the discharge steadiness more efficiently than the conventional stability criterion that compares the slope of the static volt-ampere characteristic to the value of the external ballast resistor. To check the validity of the inferred stabilization process, a typical 4.7 cm long plasma filament operates in ambient air. Optical and electrical diagnostics are performed to investigate the discharge properties. Measurements then reveal most typical features of an actual arc discharge in air. Consequently, a numerical simulation based on a time-dependent Elenbaas - Heller equation allows calculation of the time-evolution of the plasma in the discharge. Finally, electron density measurements using a specific microwave absorption device confirm the high rate of ionization of the plasma: almost two orders of magnitude higher than for a typical glow discharge in free air.