Atmospheric pressure self-organized filaments in dielectric barrier discharge excited by a modulated sinusoidal voltage

Excited by a modulated sinusoidal voltage, self-organized filaments are generated in a parallel plate dielectric barrier discharge with a flowing mixture of argon and nitrogen at atmospheric pressure. With increasing off time of the modulated voltage, a single filament transits into a pair of filaments. Then, the self-organized filaments undergo a scenario from triangle, quadrilateral, pentagon, hexagon, and finally, to a ring composed of rotating filaments. During the transition process, the discharge current always presents a single pulse per half voltage cycle, whose amplitude increases for both positive and negative discharges. However, discharge current symmetry deteriorates. Moreover, with increasing off time, the inception voltage increases for the positive discharge, while it decreases for the negative discharge. For the hexagonal arranged filaments, temporal evolutions are implemented for the positive and negative discharges. The results reveal that the initiation in one current pulse seems to propagate opposite to the gas flow direction in the positive discharge, while advances along it in the negative discharge. By optical emission spectroscopy, the electron temperature and electron density are investigated via Boltzmann plotting and a line ratio from 738 nm to 750 nm, respectively. With increasing off time, both of them increase for the positive discharge, while they decrease for the negative discharge. What is more, both electron temperature and electron density increase as the inception voltage increases.