Streamer-to-filamentary transition and electron temperature measurement in positive polarity nanosecond surface discharge between 1 and 10 bar

The paper studies streamer-to-filament transition in the single shot surface nanosecond dielectric barrier discharge (nSDBD) at high pressures, P = 1 − 10 bar. The high voltage nSDBD at atmospheric pressure develops as a set of parallel plasma channels — streamers, with electron density about n_e = 10¹⁵ cm⁻³ and typical streamer channel diameter around 100 µm. With pressure or voltage increase, a streamer-to-filament transition is observed, when, during 1 − 2 nanoseconds, a system of bright thin channels (filaments) is formed instead of the set of the streamers. The electron density rises up to n_e = 10¹⁸ −10¹⁹ cm⁻³, and according to our estimates, the diameter of the filament do not exceed a few tens of microns. The present paper is devoted to systematic experimental study of the streamer–to–filament transition in N2:O₂ mixtures, the percentage of oxygen being between 0% and 20%. The electron temperature in the discharge and near afterglow is measured in molecular nitrogen at gas pressure P = 6 bar from the Boltzmann the optical emission spectroscopy.