Investigation on the effects of the operating conditions on electron energy in the atmospheric-pressure helium plasma jet

Abstract

This work presents a numerical investigation on the effects of the operating conditions on electron energy in the atmospheric-pressure helium plasma jets based on a needle-plane discharge system. The investigation is carried out by using a 2-D fluid model. The considered operating conditions refer to the needle radius, the gap width, and both the inner diameter and the relative permittivity of the dielectric tube. The mechanisms governing the operating condition effects of electron energy have also been analyzed in detail. This work gives the following significant results. The needle radius has only a slight effect on the averaged electron energy whether in the entire plasma jet or in the plasma bullet. The averaged electron energy decreases obviously with the increase in the gap width. The effect of the dielectric tube on electron energy becomes evident only when its inner diameter is smaller than 4 mm in the present simulation. The relative permittivity of the dielectric tube slightly affects electron energy. In particular, the present work shows that the plasma bullet has a substantial contribution to high-energy electrons in contrast to the other region in the plasma jet. This is of importance for the study on the mass transfer of the reactive species in the aqueous solutions in plasma biomedicine because in the mass transfer, the penetration depth of the reactive species can be improved via the dissociative electron attachment to water molecules when increasing the electron energy in plasmas, which helps deliver the reactive species to the surface of living matter and even into its interior for inducing the expected biomedical effects.