ICCD microscopic imaging of a single micro-discharge in surface coplanar DBD geometry: determination of the luminous diameter of N(2) and Ar streamers

Time-resolved images of a single-surface dielectric barrier micro-discharge were obtained by employing ICCD microscopy with high spatial and time resolution. The micro-discharge was repetitively produced using amplitude-modulated ac high voltage waveforms applied to the coplanar electrode geometry in a reactor, fed either with high-purity Ar or N2 at atmospheric pressure. The driving high-voltage amplitude was set to initiate just one single micro-discharge per one ac half-cycle. Images recorded within the two successive ac cycles provided evidence that the track left by the first micro-discharge influenced the propagation trajectory of consecutive streamers. Images of individual micro-discharges allowed evaluation of the luminous streamer channel diameter and its evolution along the streamer's propagation trajectory. Minimum luminous streamer channel diameters of 30±6µm and 50±10µm were fixed in Ar and N2, respectively. Furthermore, direct comparison between a single micro-discharge image and an image integrating many micro-discharges allowed the estimation of potential errors associated with methods based on accumulating optical emission produced by many micro-discharge events.