Ar metastable densities (3P2) in the effluent of a filamentary atmospheric pressure plasma jet with humidified feed gas

Abstract

The Ar(3P2) metastable density in the effluent of the cold atmospheric pressure plasma jet kINPen was investigated as a function of the feed gas humidity, the gas curtain composition, and the distance from the nozzle by means of laser atomic absorption spectroscopy. The filamentary character of the plasma jet was considered as the absorption signals are from single individual events. From the effective lifetime, the quenching coefficient for Ar(3P2) by water was determined. A maximum Ar(3P2) density of (6.0±0.7)×1013 cm−3 was obtained close to the nozzle for a feed gas humidity of 20 ppm. The densities near the nozzle decreased inversely proportional to the water content in the feed gas leveling off at approximately 1×1013 cm−3, independently from the gas curtain composition. With the addition of water to the feed gas, the excitation dynamics changed, and the production and lifetime of Ar(3P2) was reduced. The impact of Ar(3P2) on the reactive species composition in the effluent was found to be smaller than within the plasma zone inside the plasma jet device.