Direct current glow discharges in atmospheric air

A microhollow cathode discharge was used as plasma cathode to sustain a stable direct current glow discharge in atmospheric pressure air. The length of the glow discharge column was varied from 1 mm to 2 cm, with the sustaining voltage increasing linearly with length. For glow discharges with currents on the order of 10 mA, the electron density in the air plasmas exceeded 10¹¹ cm^-3, with highest values of almost 10¹³ cm^-3 close to the plasma cathode. When two 8.5-mA discharges were operated in parallel, at a distance of 0.4 cm, the discharge plasmas were found to merge for electrode gaps exceeding 0.5 cm, an effect that can be used to generate large volume, homogenous air plasmas