Plasma Streamer Propagation Across Free-flowing Bubbles in Water.

Investigations into plasma dynamics confined by gaseous bubbles within a liquid medium has been of growing interest in the plasma-liquid community over the last decade. Computational investigations have demonstrated that ellipsoidal bubble shapes, along with topological deformations, result in enhanced or depleted local electric fields relative to spherical bubbles [1]. However, previous experimental methods tend to trap or hold bubbles in a manner that approximate a sphere. Our approach is to allow bubbles to flow freely, retaining their natural deformed ellipsoidal shape, and trigger a pulse generator as a function of bubble position. Plasma is generated in a bubble between a two-pin system by tripping a collimated triggering LED aligned within the path of the bubbles. Position and shape of bubbles are statistically assessed by gathering a large enough image-set of subsequent bubbles to define the boundaries of the system at time of trigger. Streamer propagation across the bubble is captured with a fast-gated iCCD camera and compared to the results of a 2D simulation previously carried out in our group using nonPDPSIM [2]. [1] N. Babaeva et al, Journal of Physics D: Applied Physics 50(36), 364001 (2017) [2] N. Pillai et al, Journal of Fluid Engineering (UNDER REVIEW).