Abstract
In the last decades, AC powered atmospheric dielectric barrier discharges (DBDs) in air with a liquid electrode have been proposed as a promising plasma technology with versatile applicability in medicine, agriculture and water treatment. The fundamental features of the micro-discharge filaments that make up this type of plasma have, however, not been studied yet in sufficient detail. In order to address this need, we investigated a single DBD micro-discharge filament over a water film in a sphere-to-sphere electrode configuration, by means of ICCD imaging and optical emission spectroscopy. When the water film temporarily acts as the cathode, the plasma duration is remarkably long and shows a clear similarity with a resistive barrier discharge, which we attribute to the resistive nature of the water film and the formation of a cathode fall. As another striking difference to DBD with solid electrodes, a constant glow-like plasma is observed at the water surface during the entire duration of the applied voltage cycle, indicating continuous plasma treatment of the liquid. We propose several elementary mechanisms that might underlie the observed unique behavior, based on the specific features of a water electrode.
Highlights
Dielectric barrier discharges (DBDs) have been intensively investigated for many decades, due to their wide applicability in several industrial processes
We investigated an AC powered single dielectric barrier discharges (DBDs) micro-discharge filament over a water film by means of electrical, spectroscopical and time- and space-resolved plasma diagnostics in combination with simulations
Since a water electrode behaves like a dielectric barrier on small time scales in the range of nanoseconds, we compared the breakdown mechanism and properties with those of a filamentary DBD micro-discharge with solid electrodes
Summary
Dielectric barrier discharges (DBDs) have been intensively investigated for many decades, due to their wide applicability in several industrial processes. Reports on the diagnostic investigation of DBD plasma with a liquid electrode in atmospheric air are scarce in scientific literature[10] This discharge type has, direct similarities with a DBD in air with solid planar parallel electrodes, such as its usually filamentary nature. The actual conductivity can be significantly different from the initial conductivity, since plasma treatment of the solution raises the conductivity to a few hundreds of μS/cm This makes the water electrode act as a dielectric on nanosecond scale, a range in which breakdown occurs for a DBD with solid electrodes. Cathode-directed positive streamers are characteristic for AC dielectric barrier discharge between solid planar electrodes, independently of voltage polarity during each sine half cycle[12]. On the other hand, only occur for specific electrode configurations, such as the multipoint-to-plane geometry in[16]
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