Electron Density and Electric Field Measurement of Space-Time-Controlled Single-Filament Streamer Discharge in Atmospheric-Pressure Air

The detailed measurement of the electron density and electric field for streamer discharges in the atmospheric-pressure air is essential for the fundamental understanding of the production mechanisms of the chemically reactive species utilized in wide ranging application fields. However, the direct measurement of the electron density and electric field has been formidable challenge for the air streamer discharge due to its irreproducible, complex branching structure. Although thorough comparison between the measurement and numerical simulation is crucial for examination of existing simulation models and development of a complete simulation code, such a systematic study has been extremely difficult. Recently, a dice-five plasma generator was developed for the realization of non-branching, straight single-filament streamer discharges reproducibly. Furthermore, the direct, combinational measurement was achieved by the application of two original measurement instruments: Talbot interferometers capable of visualizing a two-dimensional electron density distribution from a single-shot recording and a 1D electric-field induced second harmonic generation (E-FISH) sensor with one-order-superior spatial resolution and quantified measurement accuracy. Here, the direct, combinational measurement of the electron density and electric field was conducted for capturing the dynamic evolution of a single-filament streamer discharge in a secondary phase with spatiotemporal varing scales of ∼1 ns and 100 μm. The measurement data were used for the detailed examination of existing simulation models and the clarification of the fundamental governing mechanism behind the secondary streamer discharge in the atmospheric-pressure air.