Behavior of Electrons in the Bullet in the Ar/O₂ Plasma Jet in Changing Oxygen Concentration and the Applied Voltage

This work presents a systematic numerical investigation on the behaviors of electrons in the bullet in the Ar/O ₂ plasma jet in changing oxygen concentration and the applied voltage, based on a needle-plate discharge configuration and a 1-D particle-in-cell Monte-Carlo collision (PIC-MCC) method. The increase in oxygen concentration allows more electrons to be scattered toward the target, i.e., more electrons to most probably interact with the target, and induces a dramatic increase of reactive oxygen species (ROS), but leads to the decrease of the bullet velocity and average electron energy. In addition, there is a weak correlation between the electron density and ROS generation. When increasing the applied voltage, the electrons scattered toward the target decrease, however, the majority of these electrons, above 70%, are of energy higher than the threshold inducing a dissociative electron attachment (DEA) to water molecule, and meanwhile, there is an evident increase of high-energy electrons being able to excite water molecules. Also, there is a strong correlation between the electron density and ROS generation. The present results are also compared with those in the Ar/H ₂ O plasma jets, indicating qualitative and quantitative differences.