Experimental study of transient surface charging during dielectric barrier discharges in air gap in needle-to-plane geometry

Abstract

Motivated by a deeper understanding of plasma-surface interactions, this study presents experimental investigations into the transient surface charging process during dielectric barrier discharges (DBDs) in an air gap in a needle-to-plane geometry based on a combination of the Pockels method and a custom-designed ultrafast multi-frame imaging system. We realized three-frame observations of transient surface charge distributions, with a remarkable temporal resolution of 3 ns, during positive primary discharges and negative reverse discharges when applying a positive square-wave pulse. During the positive primary discharges at the rising voltage front, following the circular expansion of the streamer over the surface, multiple streamer filaments bifurcate simultaneously from the center, resulting in a branched positive surface charge distribution. Gradient surface charge densities are observed along the channel with higher charge densities at the head, which gradually evolve into a uniform distribution along the channel as the streamers approach stagnation. No lateral expansion of positive charges is observed across the channel under the present condition. In the case of negative reverse discharges occurring at the falling edge of the voltage pulse, the neutralization of residual positive surface charges and the accumulation of negative surface charges occur simultaneously in the central region. The deposited negative surface charges exhibit a progressively expanding circular distribution characterized by increasing charge density and radius. The propagation dynamics of surface streamers and the fields induced by surface charges are investigated and discussed based on the spatio-temporal surface charge measurements. Further study suggests that the surface streamer is not driven by the over-accumulation of surface charges, but rather by the space charge field above the dielectric. The presented quantitative measurements can be used for detailed validation of DBD simulations and offer deeper insights into plasma-surface interactions.