Splitting of ionization waves at the edge of a dielectric plate oriented at grazing angles between the helium plasma jet and the plate

Abstract

In this paper, we discuss the results from the two-dimensional computational investigation of the effects of a helium plasma jet interacting with a dielectric plate at a floating potential. The plate is oriented at grazing angles formed between the plasma plume and the plate. We show that for angles α > 70° the jet plasma envelopes the plate and the splitting of an ionization wave (IW) at its edge is observed. As a result, one of the IWs propagates at some elevation over the upper surface of the plate. The other IW slides along the bottom surface as a surface discharge. This effect is partially attributed to the electric field direction and buoyancy forces which are especially important for the light helium channel surrounded by air. As such, the treatment of the top and bottom surfaces is not identical even for the horizontally oriented plate (α = 90°). We discuss the production and delivery to the plate surfaces the charged and neutral species important for applications. For the conditions considered, both sides of the plate are treated simultaneously. We also show that the buoyancy forces affect the reactive oxygen and nitrogen species distributions. For the helium jet which bends upward due to these forces, the best results for simultaneous treatment of thin plates can be achieved at grazing angles α = 80°–83°, but not at the angle of 90°. The choice of these particular incidence angles can provide better results. Locating the plate horizontally in parallel to the plasma jet axis can be dis-advantageous.