Characteristics of atmospheric pressure air discharges with a liquid cathode and a metal anode

Electrical and optical emission properties of a burning plasma between a liquid cathode and a metal anode are presented in this paper. The plasma has constricted contact points at the liquid cathode and is clearly filamentary in nature near the water surface. The cathode voltage drop depends on conductivity rather than pH and is significantly different for distilled water and electrolyte solutions. An acidification of the liquid due to the plasma is always observed. The rotational temperature of OH and N₂ in the bulk of the plasma is, respectively, in the range 3200-3750 K and 2500-2750 K. The rotational temperature of nitrogen near the metal anode is typically two times smaller. Electron densities near the cathode measured by Stark broadening of H_β are in the range (5.5-8.0) × 10¹⁴ cm ^-3, the atomic excitation temperatures in the range 5750-7250 K. Differences in electrical and optical emission properties between the cases when distilled water and electrolyte solutions are used as cathode are discussed in detail.