Repetitively nanosecond pulsed discharge along dielectric surfaces: discharge and surface charge dynamics and local streamer-to-filament transition

The discharge and surface charge dynamics, as well as the local streamer-to-filament transition of a three-electrode surface discharge under repetitive nanosecond pulses with a frequency of 1 kHz at atmospheric pressure, are studied through experiments and simulations. Evolutions of plasma morphology and electric field vector, as obtained by an intensified charge-coupled device camera and an improved electric field induced second harmonic method, respectively, are utilized to analyze discharge dynamics. A 2D fluid model combined with a 0D kinetic model is established to study the accumulation behavior of surface charge and mechanism of the local streamer-to-filament transition. The simulation results demonstrate a qualitative agreement with the experimental measurements on the discharge evolution, waveforms of discharge current and key features of the electric field. The results show that a three-electrode surface discharge includes three discharge phases: the primary streamer, local enhanced discharge and reverse breakdown. The local enhanced discharge occurs near the high-voltage (HV) electrode, characterized by a local streamer-to-filament transition and subsequent emission belt parallel to the edge of HV electrode, after the primary streamer bridges the two electrodes. The local streamer-to-filament transition is attributed to the local accumulation of active species with a lower threshold energy in the high field region (∼25 kV cm−1) similar to that of the secondary streamer in pin-plane discharges. The emission belt is formed by the high-density charge spot at the filament head, a phenomenon attributable to charge migration under the influence of an applied electric field. The spatial non-uniformity of plasma channel is a general feature in non-uniform field discharges and is a key process that induces the discharge mode transition.