On the Active Species Concentrations of Atmospheric Pressure Nonequilibrium Plasma Jets

Atmospheric pressure nonequilibrium plasma jets (APNP-Js), which generate plasma in open space rather than in a confined discharge gap, are recently a topic of great interest. However, researchers actually know little about the bright plasma plume in the beginning. Fortunately, after about one decade of researches, the main active species concentrations of APNP-Js are measured. Although the measurements are carried out for different plasma jet devices and under different experimental conditions, it still gives us some insight information about the plasma plumes. In this paper, the measurements on the concentrations of the main active species such as electron, O atom, OH, ${\rm O}_{2}(^{1}\Delta _{g})$ , metastable state He and Ar, nitric oxide (NO), metastable state ${\rm N}_{2}({\rm A}^{3}\Sigma _{u}^{+})$ , and N atom for different experimental conditions are reviewed. The peak electron density of a microplasma plume could reach in the order of $10^{14}~{\rm cm}^{-3}$ . The O atom density is in the order $10^{14}~{\rm cm}^{-3}$ in the plasma plume but it is in the order $10^{16}~{\rm cm}^{-3}$ inside the discharge gap. The OH and ${\rm O}_{2}(^{1}\Delta _{g})$ densities are in the order of $10^{15}~{\rm cm}^{-3}$ . The metastable state He and Ar concentrations could reach the order of $10^{11}$ and $10^{12}~{\rm cm}^{-3}$ , respectively. The NO density is in the order of $10^{15}~{\rm cm}^{-3}$ in the plasma plume. It should be emphasized that all the measurements are carried out under different experimental conditions and for different experimental setups.