Rotating vortices in two-dimensional inhomogeneous strongly coupled dusty plasmas: shear and spiral-density waves

Abstract

Dusty plasma experiments can be performed quite easily in strong coupling regime. In our previous work [Phys. Plasmas 21, 073705 (2014)], we numerically explored such plasmas with constant density and observed the transverse shear (TS) waves from a rotating vortex. Laboratory dusty plasmas are good examples of homogeneous plasmas however heterogeneity (e.g. density, temperature, charge) may be due to the existence of voids, different domains with different orientations, presence of external forces like magnetic and/or electric, size/charge imbalance, etc. Here, we examine how the density heterogeneity in dusty plasmas responds to the circularly rotating vortex monopoles, namely smooth and sharp cut-off. For this purpose we have carried out a series of two-dimensional viscoelastic fluid simulations in the framework of generalized hydrodynamics (GHD) fluid model. The rotating vortices are placed at the interface of two incompressible fluids with different densities. The smooth rotating vortex causes two things: First, the densities are stretched to form the spiral density waves; secondly, the TS waves propagate radially into the surrounding media according to the shear wave speed. We notice that the spiral density arms are distinguishable in the early time while later get smeared out. The sharp rotating vortex creates sharp shear flows which in turn favor the Kelvin-Helmholtz (KH) instability across the interfaces. In such flows for the GHD system, the interplay between the emitted TS waves and the vortices of KH instability distorts the formation of the regular spiral density arms around the rotor