Interfacial Coupling and Non-capillary Wave Dynamics drive Dynamic Plasma Patterns at a Plasma-Liquid Interface

When an atmospheric-pressure plasma is formed with a conductive liquid electrode, the plasma can self-organize into a variety of both static and dynamic patterns that the complex electrostatics at the plasma-liquid interface. Furthermore, the pattern behavior depends intimately on the liquid properties, including its conductivity and surface tension. Under certain conditions, resonant coupling occurs between the plasma and surface waves on the liquid, causing a low-frequency plasma oscillation between a continuous annular ring and four individual spots. The measured frequencies are an order of magnitude lower than predicted by capillary wave theory, but exhibit the same damping behavior with respect to liquid viscosity, indicating that the plasma is stimulating a new class of surface waves on the liquid. A theory that includes a curvature-dependent Maxwell pressure mechanism exerted by the plasma on the liquid produces a dispersion relationship that effectively collapses the experimental data across a wide variety of experimental conditions.