The Study On A Novel Direct Current Discharge In Ambient Air

Atmospheric pressure discharges are widely used in many fields because they do notneed expensive vacuum equipments and are easy to operate. But most atmospheric pressuredischarges still need to use inert gases to make discharges stable and uniform. So it is verysignificant to generate uniform discharges in ambient air.Discharges will have different characteristics if discharge parameters such as, electrodesfiguration, power supply, gas used and discharge circuit are different. In this paper, stabledischarge is generated which shows a unique profile that has not been reported before. Thedischarge looks like an umbrella. Only the outside layer is luminous while the inside is dark.Discharge is ignited between a copper electrode with hemispherical head and water electrodeonce the air gap is broke down, using direct current power supply. Ballast resistor in the orderof MΩis used to perform a negative freedom mechanism to stabilize the discharge. Afterbreakdown, the discharge will be very stable and silent. The discharge is composed of threezones with different luminosities. Discharge current is in the order of mA.The effects of discharge current, air gap length, cathode dimension and electricalconductivity of the water electrode on the discharge are studied. Volt-ampere characteristicsand images of the discharge under different experiment conditions are shown to characterizethe discharge. The mechanism for the stabilization of the discharge is also discussed.Discharge cone will shrink into a thin column if discharge current is large enough. At thesame current, diameter of the discharge cone increases with diameter of the copper electrodeand air gap length. While electrical conductivity of the water electrode is lower than 17.31μs·cm^-1, the discharge is still conical but no longer hollow. The whole plasma region isluminous and dark region can not be seen any longer.Vibrational and rotational temperatures of N₂ can be calculated by means ofBoltzmann plot method according to the second positive band of N₂(C³ÐŸ_u→B³ÐŸ_g) andthe (0, 0) band of the first negative band of N₂⁺(B²âˆ‘→X²âˆ‘), respectively. Vibrationaltemperature is 2455K at the following discharge parameters: diameter of copper electrode andair gap length are all 5 mm, electrical conductivity of water electrode is 273.15μs·cm^-1 anddischarge current is 1.9 mA.