Atmospheric pressure glow discharge in air using a water electrode

An atmospheric pressure glow discharge in air is generated between the surface of a water electrode and a metal electrode with a high alternating current (60 Hz) voltage (<20 kV). The gap distance between the two electrodes can be adjusted from 3 mm to a few centimeters. The diameter of the plasma column is in the 3-10 mm range. Photographs taken with a high-speed charge coupled device camera clearly show a cathode fall region, negative glow, positive column, and anode dark space; a structure consistent with that of a normal glow discharge. The initial breakdown process shows that the plasma ignites at the water surface and terminates at the metal electrode. The N₂ rotational and vibrational temperatures were spectroscopically measured to be about 1800 and 2600 K, respectively.