Spatial‐temporal evolutions of surface discharge patterns generated on dielectric target interacted with a plasma jet

With increasing peak voltage applied to a plasma jet, surface discharge patterns are formed on the dielectric target, which include diffuse spot, single ring, and concentric triple rings. During the evolvement of these patterns, the number of positive current pulses increases and there is only one negative pulse per voltage cycle. Fast photography reveals that all of these patterns originate from temporal superposition of negative and positive surface discharges. The negative surface discharge is always diffused for each pattern. However, the positive surface discharges in a streamer regime are more complicated. The first positive streamer per voltage cycle is short, which propagates along radial spokes that are distributed symmetrically, resulting in a central spot of each pattern. The last positive streamer per voltage cycle is long, which propagates along a straight line at a lower peak voltage and bifurcates randomly at a higher peak voltage, resulting in diffuse background of each pattern. Other positive streamers also bifurcate after traveling certain distance from the center, and then propagate along an arc, leading to the formation of ring in patterns. The propagation behaviors of these positive streamers are discussed qualitatively by analyzing the influence of applied electric field, residual charges, and air diffusion.