Downstream characterization of an oxygen atmospheric pressure plasma jet

Abstract

The characterization of the downstream of an oxygen atmospheric pressure plasma jet (APPJ) is performed. This APPJ is sustained by pulsed power with a repetitive frequency up to 25 kHz. The reactivity of the plasma at different operating conditions is characterized using the intensities of O2 (759 nm) and O (777 nm) optical emission lines. The jet downstream temperature is measured by a thermocouple. It is shown that the intensity of O2 emission is not sensitive to the flow rate while it increases with the increase in the applied voltage. O emission is only observed at high flow rate. The temperature measurement shows that it slightly increases with the applied voltage. At the jet exit, the temperature monotonically increases with the flow rate while at 1 cm downstream of the jet, it shows an opposite trend. It is shown that the existence of an external surface at the downstream greatly influences the emission spectra adjacent to the surface. When the jet downstream is shielded with a glass tube, the O radical emission intensity increases by more than one order of magnitude. Preliminary studies show that the presence of the surface potentially enhances certain surface reactions. Such an enhancement leads to the increase of the O radical density, as suggested by the spatial-resolved optical emission spectra.