Two-dimensional electron density measurement of pulsed positive primary streamer discharge in atmospheric-pressure air

Elucidating the electron density of streamer discharges propagating in atmospheric-pressure air is critical for achieving a systematic understanding of the production mechanisms of reactive species. Using Shack–Hartmann-type laser wavefront sensors with a temporal resolution of 2 ns, we carried out single-shot two-dimensional electron density measurements for positive primary streamers generated in a 13 mm air gap between pin-to-plate electrodes. The electron density over the positive primary streamers decayed from 10¹⁵ to ${10}^{14}\text{c}{\text{m}}^{-3}$ during the propagation. The decay time constant of the electron density in the primary streamer channels was estimated to be  ∼2 ns. The distribution widths of the electron density were in good agreement with those of the light emission, typically ranging from 0.8 to 1.5 mm. (paper)