Electrical and optical characterization of a pulsed discharge in immiscible layered liquids : n-heptane and water with various electrical conductivities

Abstract

In-liquid pulsed nanosecond discharges produce highly dynamic plasmas that can be applied in different fields. In this study, we investigate the discharge dynamics of plasmas generated at or near the interface of water (with various electrical conductivities) and liquid heptane. The results indicate that at low conductivity (⩽100 μS cm−1), the discharges are most successful when the anode tip is in water and close to the interface. Under these conditions, the plasma shape is filamentary, i.e. streamer-like. Meanwhile, at high conductivity (⩾500 μS cm−1), the highest percentage of successful discharges is observed for the case where the anode tip is in heptane, near the interface. The plasma generated under these conditions takes the shape of one wide and intense filament, i.e. spark-like. The transition from streamer-to-spark mode is also confirmed by electrical and optical measurements. Using a negative polarity, the highest percentage of successful discharges is generated in low-conductivity water, near the interface. When the conductivity is increased, the success rate of discharges reaches 100%, if the cathode pin is kept in water.