Characteristics of DC discharges with a liquid cathode and a metal anode

We will present the characteristics of atmospheric pressure direct current (DC) discharges generated between a liquid cathode and a metallic anode. Plasma is generated by purging helium (He) gas through a tungsten tube. The discharge characteristics are investigated by varying applied voltage, U, gas flow rate, inter-electrode separation, gas mixture, and cathode properties (distilled water and sodium chloride as the cathodes). At He flow rates of 800-1600 sccm and voltage U up to 3.5 kV, the glow has the form of a circle on the surface of distilled water. At higher applied voltages, a conical shape is formed. The circular and conical shapes disappear with increasing the electrode separation and the He flow rates. Mixing N₂ or air from the surrounding tube flow results in the disappearance of the circular and conical shapes formed on the water's surface. With sodium chloride solution as the cathode, the discharge spreads in the form of a circle at a lower applied voltage. It transforms to a yellowish conical shape at higher voltages. Liquid cathode discharges are often subject to hydrodynamic instabilities, which result in the ejection of liquid droplets into the plasma. Our experimental observation could give helpful insight into the mechanism of droplet generation and the transport of metal atoms from the solution to the plasma. Modeling some aspects of the discharge has been performed using computational tools available to the team. A comparison of simulation results with electrical and optical measurements is being conducted to explain the observed characteristics.