Plasma conductivity as a probe for ambient air admixture in an atmospheric pressure plasma jet

Abstract

By utilizing a fully floating double electrical probe system, the conductivity of a linear atmospheric pressure plasma jet, utilizing nitrogen as process gas, was measured. The floating probe makes it possible to measure currents in the nanoamp range, in an environment where capacitive coupling of the probes to the powered electrodes is on the order of several kilovolts. Using a chemical kinetic model, the production of reactive nitrogen oxide and hydrogen-containing species through admixture of ambient humid air is determined and compared to the measured gas conductivity. The chemical kinetic model predicts an enhanced diffusion coefficient for admixture of O2 and H2O from ambient air of 2.7 cm2 s−1, compared to a literature value of 0.21 cm2 s−1, which is attributed to rapid mixing between the plasma jets and the surrounding air. The dominant charge carriers contributing to the conductivity, aside from electrons, are NO+, NO2 − and NO3 −. Upon admixture of O2 and H2O, the dominant neutral products formed in the N2 plasma jet are O, NO and N2O, while O2(1Δg) singlet oxygen is the only dominant excited species.