Hexagonal arrayed patterns with bright and dark spots observed in a compact plasma reactor based on a piezoelectric transformer

Abstract

In this paper, we describe the formation of hexagonal arrayed patterns in a compact plasma reactor that consists of a piezoelectric transformer (PT) and a dielectric electrode. A high voltage induced on the PT surface by the piezoelectric effect generated diffuse glow-like and patterned dielectric barrier discharges (DBDs) in a gap. Vacuum ultraviolet (VUV) spectroscopy was applied to observe light emitted from and excimers, which were formed in a He–Xe mixture and pure Ar, respectively. Peaks at 172 and 126 nm were observed in the emission spectra. Hexagonal arrayed patterns were observed in both He and Ar by adding a small amount of air. Then, static and time-resolved images of the hexagonal arrayed patterns were captured using a single-lens reflex camera and an intensified charge-coupled device camera, respectively. The hexagonal arrayed patterns alternately exhibited bright and dark spots in weak uniform emission on the PT surface depending on the applied sinusoidal voltage. Both patterns were similar in the observed time-resolved images. Thus, it was confirmed that the observed dark spots were the traces of accumulated charges on the PT. Here, we discuss the necessary conditions for the generation of such patterns in terms of the charges accumulated on the PT and compare our results with those reported elsewhere.