Experimental observation of interfacial oscillations and self-organization derived from streamer-driven mechanical perturbation of a gas–liquid boundary

Abstract

Plasma discharges in bubbles remain an active area of research because of the associated applications in environmental remediation, agriculture and chemical processing. Plasmas in contact with the gas–liquid interface can drive chemical and physical processes, one of which is the mechanical surface perturbation leading to the formation of capillary waves. Using a 2D discharge cell, capillary waves on the surface of a 2D bubble are investigated. This study reports the observation of interfacial capillary waves on the gas–liquid interface excited by nanosecond pulsed plasma discharges. The capillary waves appear to be initiated by streamers coming into contact with the interface, with surface tension playing the role of the restoring force and viscosity contributing to damping. The waves propagating along the bubble’s surface alter the bubble’s shape. This capillary wave mode was found to be dependent on bubble size and plasma pulse frequency. Sympathetic resonant oscillations were also observed in adjacent bubbles, which indicate that capillary waves can drive acoustic oscillations and ultimately drive large-scale fluid effects. Additionally, strong surface perturbation was observed to modify the breakdown gap and as a result, led to self-organization of subsequent plasma streamers, which in turn sustains the capillary waves. In effect, plasma streamers and capillary waves are positively coupled to each other as a form of feedback, thus give insight into the interplay between plasma and fluid effects.