Spatial and temporal dynamics of single nanosecond discharges in air with water droplets

Abstract

Discharges generated in water or water-containing media have great potential for various technological applications. However, a fundamental understanding of plasma-liquid interactions, particularly the ignition and propagation of a discharge in a gap containing liquid droplets, is lacking. This study investigates the electrical characteristics and the spatial-temporal dynamics of nanosecond discharges in air containing one or two millimetric droplets of deionized water. Analysis of the effects of voltage amplitude (Va) and pulse width on the discharge mode shows that at low Va, the discharges are run in streamer mode; however, at high Va, a streamer-to-spark transition is observed. Although the droplet size (diameter between 2 and 4 mm) does not significantly influence the discharge dynamics, its position with respect to the gap (on- or off-axis) has a strong effect. Time-resolved imaging of three droplet configurations (one on-axis droplet, one off-axis droplet, and two on-axis droplets) was used to unveil the ignition and propagation dynamics of streamers and sparks at nanosecond time scale. The findings are of interest and contribute to a better understanding of` the plasma-droplet interactions, which is crucial for the development and optimization of plasma-based applications.

Propagation of nanosecond discharge in an air gap containing a water droplet: modelling and comparison with time-resolved images

“…The experimental setup used to produce single discharges in air with a water droplet is detailed in [20], therefore, only a brief description is presented here. The discharge is produced between copper electrodes using single pulses generated by a negative polarity power source (NSP 120-20-N-500-TG-H; Eagle Harbor Technologies) at −11 kV amplitude and 300 ns pulse width.…”

“…The authors show that the discharge is initiated in the air gap between the anode and the droplet, then it propagates over the droplet. In 2023, Hamdan and Dorval [20] have also studied the spatio-temporal dynamics of a nanosecond discharge in air with a water droplet lying on a Teflon surface. The authors found that the discharge is ignited as streamer at the electrodes and reached the droplet within few nanoseconds.…”

Oil–water interface dynamics and electrical breakdown in pulsed electric field

“…The wetted wall condition is specified at boundaries 1, 3,5,6,14,15,16,17,24,25,26,27 in the Navier slip form:…”

“…An interface between gas, liquid, or solid inside the gap can significantly reduce its dielectric strength. Efforts have been focussed on investigating the role of distributed gas phase and polarity on breakdown development [14][15][16][17][18], as well as studying the plasma at the liquid surface [19][20][21][22][23][24]. StillElectrical breakdown across the interface of dielectric liquids has still not been studied broadly [25].…”

Atmospheric pressure plasmas interacting with wet and dry microchannels: reverse surface ionization waves

“…This local electric field then initiates and sustains the propagation of a surface ionization wave (SIW) [10]. Several recent studies have focused on the propagation of SIWs over non-planar dielectric surfaces [11][12][13]. In addition to charge accumulation, non-planar dielectric surfaces polarize when exposed to an electric field, which then produces electric field enhancement at locations with positive curvature and small radii [14].…”