Characteristic study of a transient spark driven by a nanosecond pulse power in atmospheric nitrogen using a water cathode

In this paper, a transient spark discharge is presented driven by a nanosecond pulse power with a needle-water electrode configuration in atmospheric nitrogen. The transient spark discharge concludes three phases, described as the streamer phase, the streamer-to-spark transition phase, and the spark phase. The amplitude of pulse voltage has a significant influence on the characteristics of the transient spark discharge. The streamer-to-spark transition time shortens with the increase of pulse voltage, and the spark current value increases with the increase of pulse voltage. Though the streamer-to-spark transition is not completely prevented, the gas temperature is still in a lower value (∼400 K), due to the short duration of spark current (200-400 ns). The electron density in the transient spark, calculated by the Stark broadening of the H _α line at 656 nm, is about 1.3 × 10 ¹⁷ cm ⁻³ , which is 2-3 orders of magnitude higher than that in other forms of gas-liquid discharge. The results indicate that the transient spark discharge plasma is in a highly non-equilibrium state and the results also present its other unique features of high electron density and abundant excited species.