Experimental study of the influence of O₂ content on electrical and optical characteristics of He/CF₄ APPJ

Abstract

CF4 is an important source of reactive F-containing species (RFS) so that it is used to mix with inert gas as the working gas of atmospheric pressure plasma jet (APPJ) for material surface fluoridation modification. The addition of a small amount of O2 can increase the density of RFS in He/CF4 APPJ. Therefore, the hydrodynamic, electrical and optical properties of He/CF4/O2 APPJ interacting with the dielectric are experimentally investigated in this paper. Meanwhile, the influence of the excitation source on plasma discharge is discussed in detail and the internal mechanism of the experimental phenomenon in this paper is analyzed using the simulation results based on the model established in the previous paper. It is found that the addition of a small amount of O2 can increase the intensity and accelerate the axial propagation speed of He/CF4 APPJ due to the low ionization energy of O2 and the increase of the Penning ionization between metastable He and O2. With the increase of O2 content, the stability of the discharge is gradually enhanced due to the electron attachment reaction of O2 and the position of the primary current pulse in each half voltage cycle gradually approaches the position of the peak voltage because the increase in O2 content raises the breakdown threshold in dielectric barrier discharge (DBD) region. In the presence of downstream dielectric, the addition of 0.1%O2 does not significantly change the radial development radius of APPJ due to the higher electron attachment rate and electron collision excitation loss power. The discharge pulse intensity is generally reduced compared to the absence of dielectric and the glow discharge in the strict sense no longer exists. The continuous spectrum intensity of RFS increases with the addition of a small amount of O2 while decreases significantly when O2 content is too high.