1D fluid model of RF-excited cold atmospheric plasmas in helium with air gas impurities

Abstract

Cold atmospheric plasmas (CAPs) in helium with air gas impurities (He+Air for abbreviation) compromise the discharge stability of helium and the chemical reactivity of air, having great prospects for various applications such as plasma biomedicine. However, different kinds of reactive species are produced in He+Air CAPs but only a few of them could be measured, and the plasma chemistry is so complex that the reported simulation models are simplified to a large extent, such as neglecting the space variation of CAPs by using a 0D model. As a result, much remains unknown for He+Air CAPs, which hinders the development of their applications. For that reason, a 1D fluid model of He+Air CAPs is developed in this paper, incorporating 48 chemical species and 118 volume reactions, which are extracted from a complex chemistry set by a reported 0D model, and then the density distribution of reactive species, the power dissipation pathways, and the chemistry pathways among the reactive species are obtained as a function of air concentration from 500 to 10 000 ppm. It is found that O and NO are the dominant reactive oxygen species (ROS) and reactive nitrogen species (RNS), respectively. Taking the ROS as a whole, it is mainly produced by the electron impact dissociation and excitation of O2; taking the RNS as a whole, it is mainly produced by the oxidation of atomic nitrogen [N and N(2D)], and NO is the precursor for all the other RNS.