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

Abstract

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 Hα line at 656 nm, is about 1.3 × 1017 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.

Mode transition and plasma characteristics of nanosecond pulse gas–liquid discharge: Effect of grounding configuration

“…Therefore, the measured voltage during the streamer‐to‐spark transition is related to the voltage of capacitors. When a direct grounding configuration is used, a transient spark discharge can be achieved, which is shown in Figure a,b, whose characteristics have been reported in our previous work . And in the direct grounding configuration, the streamer phase of the transient spark discharge dominates at a low pulse voltage (<28 kV), and the current of the streamer is higher than that of the spark.…”

“…Spectrum at 656 nm corresponding to the H α line is used to calculate the electron density, and the relation between the electron density n e and the full width at the half area (FWHA) of the line profile is obtained by the following equation: where denotes the Stark broadening expressed in FWHA. The Stark broadening in FWHA can be determined through Equation , as the H α line in our experiment is approximate to a Lorentzian profile …”

“…In the direct grounding configuration, a strong discharge channel throughout the discharge gap appears, along with multiple discharge filaments around the quartz tube. Owing to the long exposure time of camera (0.1 s) compared with the duty cycle of pulse voltage (0.0083 s), the images taken from the direct grounding configuration include the streamer (filaments morphology) and spark phases (strong shrinking discharge channel) of the transient spark mode . This form of discharge is defined as a transient spark discharge according to its waveforms of discharge current, which are presented and discussed in the following section.…”

“…Whether the dielectric can suppress discharge mode transition in gas–liquid discharges is still unclear. A transient spark mode was reported in the gas–liquid discharge with a dielectric‐free configuration . In this discharge mode, a streamer‐to‐spark transition occurred, indicating that the discharge was unstable.…”

Spectroscopic Characterization of an Atmospheric Pressure Plasma Jet Used for Cold Plasma Spraying

“…where the electron density is n e in cm −3 , and the Stark broadening is at its full width at half area ∆λ A S in nm. A deconvolution of the measured line profile and the determination of ∆λ A S was performed as described in [26][27][28]. In this experiment, nitrogen with the addition of 1% hydrogen (Linde AG, Pullach, Germany, ≥99.999%) was used as a working gas, and measurements were taken at a distance of 2 mm from the nozzle.…”