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 10(15) to 10(14)cm(-3) during the propagation. The decay time constant of the electron density in the primary streamer channels was estimated to be similar to 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.