Filamentation of Diffuse $\hbox{He}-\hbox{H}_{2} \hbox{O}$ Atmospheric Pressure Glow Discharges in a Metal Pin–Water Electrode Geometry

The filamentation of a microsecond pulsed He- H
₂
O glow discharge generated in a metal pin-water surface configuration is studied by fast imaging and current-voltage measurements. The instability leading to the constriction of the glow discharge starts from the metal electrode independent of the polarity. The dynamics of the constricted channel share similarities with plasma bullets and streamers, but the timescales are typically an order of magnitude slower due to the space charge of the glow discharge.