This article reports on experiments in a nonequilibrium plasma produced by nanosecond repetitively pulsed (NRP) spark discharges in water vapor at 450 K and atmospheric pressure. The objective is to determine the electron number density in the post-discharge, with spatial and temporal resolution, to gain a better understanding of the discharge development and chemical kinetics. Electron number densities were measured in water vapor from the broadenings and shifts of the H α and H β lines of the hydrogen Balmer series and of the atomic oxygen triplet at 777 nm. For an average reduced electric field of about 150 Td, high electron densities up to 3 × 1018 cm−3 are measured at the cathode, up to 5 × 1017 cm−3 at the anode, and up to 4 × 1016 cm−3 in the interelectrode gap. The high density near the electrodes is attributed to ionization enhancement and secondary electron emission due to the high electric field in the plasma sheath. In the middle of the inter-electrode gap, we show that the electron density mainly decays by electron attachment reactions. The dissociation fraction of water vapor is estimated to be around 2% in the middle of the gap.

Recent research in plasma biology proved that atmospheric pressure plasma jets (APPJs) have a biocidal effect, making them a promising alternative to traditional antimicapability of the APPJs, the streamer propagation, and the chemistry involved. The aim of this study is to investigate experimentally the effect of the target conductivity on the plasma characteristics: plasma jet propagation and reactive species production. The results show that the tions depend on the conductivity of the target. The results also demonstrate that the generation This study shows that the assessment of RONS generated by APPJs should be performed as close as possible to the real applications conditions.

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