Investigation on the Behavior of Electrons in the Bullet as Well as Its Dependence on Applied Voltage and H₂O Concentration in the Atmospheric-Pressure Ar/H₂O Plasma Jets

This article presents a systematic investigation on the behavior of electrons in the bullet in the Ar/H2O plasma jet in increasing the applied voltage and water vapor concentration based on a needle-plate discharge configuration and a 1-D particle-in-cell Monte Carlo method. The scattering angle of the electron in the bullet is described using the angle between the electron scattering direction and the bullet propagation direction. The following results are obtained. The evolution characteristic of the angle spectrum of electrons in the bullet in increasing the applied voltage is the same as that in increasing water vapor concentration, namely, the electrons scattered toward the target get increasingly less. When increasing the applied voltage, the OH density, the electron density, and the average electron energy $E_{\mathrm {ave}}$ increase. However, the increase in water vapor concentration leads to an evidently increasing OH density and a decrease in both the electron density and $E_{\mathrm {ave}}$ . In the range of electron scattering angles below 90° in the bullet, the percentage of electrons with energy above 3.27 eV (the threshold of inducing dissociative electron attachment to water molecule) increases with increasing applied voltage but presents a slight decrease in increasing water vapor concentration. The majority of electrons to most probably interact with the target are of energies higher than 3.27 eV. Finally, a notable effect of H2O admixture is that it gives rise to the decrease in not only $E_{\mathrm {ave}}$ but also the electron density in the bullet, especially the latter decreases evidently.