DBD-like and electrolytic regimes in pulsed and AC driven discharges in contact with water

Abstract

The interaction of an ambient air plasma with a water surface in a pin–water electrode configuration is presented in a polydiagnostic study. A discharge was generated by applying different high-voltage (HV) waveforms to a metallic pin electrode, positioned 2 mm above the water surface of a Petri dish filled with demineralized water. For pulsed discharge operation, a clear distinction is observed between a dielectric barrier discharge regime featuring a transient discharge at the rising as well as at the falling slope of the HV pulse, while a steady discharge is present in the gap during the complete HV pulse for the electrolysis regime. The occurrence of those two regimes is coupled to the increasing conductivity of the water over time, which additionally results in a quick rise of the dissipated discharge power and an increase of the gas temperature. The AC driven discharges exhibit only the electrolysis regime and do not significantly evolve over the treatment time. The resulting water conductivity was found to be a function of the total dissipated energy, irrespective of the discharge driving mode. Additionally, the resulting water conductivity shows a strong correlation with the total transferred charge in the gas phase. The total dissipated energy can potentially be used as a global measure to compare different experiments involving plasma–water interaction across different setups in different research groups.

Electron density in a non-thermal atmospheric discharge in contact with water and the effect of water temperature on plasma-water interactions

“…As the water properties are changing in time, so does the discharge. This can be observed in the previous section and in other measurements, which are published in earlier work [14], but in the electron densities as well. For all four presented discharges, the electron density increases as function of the treatment time.…”

“…There are many different configurations investigated where a gas discharge directly or indirectly interacts with water. The results presented in this work continue on a setup presented in earlier published work [14], where a polydiagnostic study on an ambient air discharge in a pin to water configuration shows a transition of the system, from a DBD-like (dielectric barrier discharge-like) configuration where the water serves as insulator, to an electrolysis driven system as the conductivity rises during the treatment of the water. An important parameter in plasma dynamics and chemistry is the density of electrons.…”

“…While the electron density measurements are the main focus of this work, the interpretation of the results benefit from a more comprehensive depiction of the discharge operating in this setup. As the experiments are performed on a similar setup used in earlier published work [14], which is referred to multiple times, this section begins with a brief summary of the experiments and results presented in this citation. At the start of the experiments, the Petri dish is filled with distilled water, which serves as a dielectric layer covering the grounded electrode.…”

“…Using Stark broadening it is possible to measure temporally and spatially resolved values for the electron density, if the intensity of the hydrogen line allows it. The ICCD imaging on this system presented in [14] shows a bright DBD-like streamer discharge propagation from the needle electrode to the surface at the developing in the first 20-50 ns of the applied pulse. However, the intensity of the H α and H β emission lines during this part of the pulse is still weak.…”

“…The function of the pulse are supplied by an arbitrary waveform generator (KEYSIGHT 33 500B) and the high voltage is supplied by a high voltage amplifier (Trek, 10/10B-HS). This setup is similar to the pulsed discharge investigated in earlier work [14]. In figure 2 Prior to generation of the discharge, the Petri dish contains demineralized water.…”