High Spatial Resolution Measurement of Electric Field Vector in Positive Secondary Streamer Discharge under Atmospheric-Pressure Air

Electric field vector measurement of a streamer discharge under atmospheric-pressure air is crucially important for systematic understanding of the production mechanisms of reactive species. However, the measurement has never been achieved for the streamer discharge, due to its irreproducible, complex branching structure. Further, measurement-accuracy uncertainty and/or low spatial resolution of conventional electric-field sensors has prevented reliable determination. Here, the reliable electric field vector measurement was first achieved for the streamer discharge by the development of two original apparatuses: a multi-anode plasma generator capable of reproducibly realizing a non-branching, straight streamer discharge and a measurement-accuracy-quantified electric-field induced second harmonic (E-FISH) generation sensor with 20-mm spatial resolution, which is one-order superior. The vector measurement demonstrated that in an initial phase of the secondary streamer discharge, the electric field inside the discharge was as high as 150±30 Td. This suggested the occurrence of ionization inside the discharge, which was supported by previous electron density measurement but inconsistent with earlier numerical simulations predicting insignificant ionization. The contradiction could be caused by the fact that the measured electron density distribution at the primary streamer contact with the cathode was different from the numerical simulations.