Abstract
Year by year, plasma processing with atmospheric pressure plasma jets is increasingly gaining attention and diversifying into various scientific and industrial fields; plasma jet systems have the merit of being able to release plasma into target liquids or solids. Thus, naturally, part of plasma jet research has directed towards investigating interfacial phenomenon between plasma–liquid or –solid and understanding underlying principles thereof. Since impinging plasma jet on the liquid surface has been considered as a basis of plasma jet processing, for example, active efforts to assess the transport of electrons and other reactive species from plasma to liquid have been made. However, despite its scientific and practical significance, surprisingly little attention has been given to the stabilizing effect of plasma jets on plasma–liquid interfaces thus far. In this contribution, we demonstrate the stabilization of liquid instabilities by weakly ionized gas for the case of a helium gas jet impinging on water, which profoundly affects the water free surface. Special attention is given to the interfacial dynamics relevant to electrohydrodynamic (EHD) gas flow, so-called electric wind, induced by the momentum transfer from accelerated charged particles to neutral gas under a strong electric field. A plasma jet consisting of periodic pulsed ionization waves, called plasma bullets, exerts more force via electrohydrodynamic flow on the water surface than a neutral gas jet alone, resulting in cavity expansion without destabilization. Furthermore, both the bidirectional EHD gas flow and parallel electric field to the gas–water interface caused by plasma interacting 'in the cavity' render the surface more stable. This case study demonstrates the dynamics of liquids subjected to a plasma-induced force, offering new insights into physical processes and revealing an interdependence between weakly ionized gases and deformable dielectric matter, including plasma–water systems, and their potential stabilization.