Generation and mechanism of a two-dimensional large-scale diffuse plume in an open air argon jet

Atmospheric pressure two-dimensional (2D) plasma jet has demonstrated its efficient performance in large-area target processing. In this study, a large-area 2D plasma jet is generated using a particularly designed device with a negative polarity pulsed power supply. Electrical and optical methods are utilized to investigate the 2D plasma jet. Both optical emission (brightness) and spatial characteristics (length/area) exhibit positive correlations with peak voltage and gas flow rate, demonstrating parameter-dependent plume expansion. The experimental results show that there exist two discharges in each voltage cycle, namely negative discharge and positive discharge, which correspond to the falling and rising edges of the voltage pulse signal, respectively. The negative discharge exhibits diffuse characteristics, and its origin and propagation are closely related to the negative streamer. The positive discharge is formed by positive streamers and propagates downstream in the form of 2D “bullets.” The differences in the morphology of the two discharges are related not only to the discharge mechanisms of positive and negative streamers but also to the active particles remaining on the surface of the dielectric layer. The plasma parameters of the 2D plasma plume are diagnosed by optical emission spectroscopy. The results show that plasma parameters such as the electron density and electron excitation temperature of the positive streamer are higher than those of the negative streamer. The gas temperature of the discharge is close to room temperature. It provides an important theoretical and experimental foundation for achieving stable and high-efficiency plasma jet operation in large-area target processing applications.