Numerical study on positive streamer in parallel-rod dielectric barrier discharge in atmospheric air

In this work, a parallel-rod dielectric barrier discharge (DBD) operating in atmospheric air is investigated through the two-dimensional plasma fluid model. The effects of applied voltage (V-p), secondary electron emission coefficient (gamma), and photoionization are examined. Photoionization can significantly influence streamer dynamics by accelerating and broadening both volumetric and surface streamers and enhance the impact of the applied voltage. Without photoionization, the propagation distance of the surface streamer along the curved dielectric surface is limited to 0.1-0.2 mm under applied voltages of 8-8.5 kV. In contrast, with photoionization, this distance can extend to 0.3-0.6 mm. Achieving the same distance requires much higher voltages (10-11 kV) if without photoionization. The "double-layer" structure of the surface streamer is investigated, revealing that gamma predominantly affects the surface branch with little impact on the volumetric branch. The critical charge density for streamer onset is found to be about 10(18) m(-3), and the volume-to-surface streamer transition is attributed to the lateral electric field provided by the space charges. This work provides insights into the regulation strategies and underlying mechanisms of streamer dynamics in parallel-rod DBDs in atmospheric air.