Understanding instability at the surface between liquid and plasma
DOI: 10.1063/10.0000177
Understanding instability at the surface between liquid and plasma lead image
The presence of a strong electric field can cause electrocapillary instability in liquid metal. This phenomenon is known as Frenkel-Tonks instability and can be caused by a plasma bordering the liquid metal – as the electric charge of the plasma ions creates a strong electric field, it can lead to instability in the liquid layer. The plasma ions also create stress on the surface of the liquid, which further alters characteristics of the instability. This process can cause the liquid to form ripples on its surface, and strong instabilities may eject droplets into the plasma.
Understanding how plasma ions behave is important for reducing instability in applications such as vacuum arcs, liquid-metal ion sources, and nuclear fusion devices. In a recent paper, Valerian Nemchinsky developed a self-consistent and more accurate description of how plasma ions interact with liquid surfaces.
In a series of calculations, he found that the plasma ions’ inertia causes them to slip off the curved electric field lines as they move, which creates shear stress upon the liquid surface. This shear stress could change the development of capillary waves in the liquid wall and might be just as important as the normal stress also caused by plasma ions.
“The shear stress ions create upon the rippled surface could change the impact of capillary waves dramatically,” Nemchinsky said.
He extended his calculations related to surface stress to determine the dispersion relation of the capillary waves, which then allowed him to predict the most dangerous wavenumbers and their corresponding instability increments. He also calculated the interval of wavenumbers in relation to the electric field and the increment of the most dangerous instability and found differences between hydrogen and deuterium plasmas.
Source: “On the stability of a liquid layer bordering plasma,” by Valerian Nemchinsky, Physics of Plasmas (2019). The article can be accessed at https://doi.org/10.1063/1.5123475 .
