Atmospheric pressure plasma jet impinging on a wavy dielectric surface: effects of DC polarities

We report a simulation study on the discharge dynamics on a wavy dielectric surface that being irradiated by an atmospheric pressure plasma jet (APPJ). Driven by a DC voltage with positive polarity, the diffusive bulk discharge splits into several separated discharge channels when propagating to the vicinity of the wavy surface, resulting from the surface morphology induced electric potential distribution. The separated discharges are intense, but also with rather poor uniformity. Alternatively, a negative voltage driven APPJ can produce a homogenous discharge near the wavy surface. Three discharge modes, namely the negative streamer, the return stroke and the surface discharge are identified, and being regulated by the surface charging and the local electric field vector. The alternate formations of the negative streamer and the return stroke lead to a zigzag radial propagation manner. Since the negative discharge can penetrate deep into the groove and delivers active species to the inner surface, the surface fluxes of the excited species such as O and N show higher and more uniform distributions. (letter)