Static and dynamic two-dimensional patterns in self-extinguishing discharge avalanches

We present experimental studies of the rich variety of two-dimensional current-density patterns that form in self-extinguishing or ‘‘silent’’ gas discharges between insulated, planar electrodes. Steady-state conditions evolve over seconds in this system, making it well suited for studies of the dynamics of non- equilibrium patterns. Because the patterns arise from nonlinear charge conduction processes in gases, the type of pattern obtained for a given set of bias parameters depends on the gas composition. While time-independent, Turing patterns are predominant in nearly pure He for the gap height used here, we find that adding ${\mathrm{H}}_2$O vapor as an impurity gas produces several types of patterns with persistent time dependence. As the drive frequency is lowered, patterns with noisy space and time dependence become increasingly common. This probably reflects an enhanced effect of space-charge fluctuations on the discharge initiation sites.