A Versatile Laminar Flow Atmospheric Pressure Plasma Jet Using a Double Coaxial Glass Tube

We report the characteristics of laminar flow atmospheric pressure plasma jets (APPJs) using a double coaxial glass tube. Two gases can be introduced independently into the tube, and the gas and plasma flows form a laminar flow and then interact outside of the glass tube. In the case of helium (He) as an inner gas flow with an outer nitrogen (N₂) gas flow, emission lines of nitric oxide, the first negative and second positive system bands of N₂ were observed, while only the second positive system band was observed in the case of argon (Ar) as the inner one. Considering the Penning effects of each excited state, the metastable state of He has a higher energy than that of Ar, resulting in energetic nitrogenous productions in the former case. The excited state in the core plasma is one of the important conditions to determine the characteristics of the APPJ produced with a double coaxial glass tube.