Dipole propagation in inhomogeneous strongly coupled dusty plasmas: A viscoelastic fluid approach

The propagation characteristics of fluid vortices-particularly monopoles and dipoles, in a homogeneous viscoelastic fluid were reported in a recent publication [Dharodi et al., Phys. Plasmas 23, 013707 (2016)]. In that study, a dusty plasma was modeled as a viscoelastic fluid using the incompressible limit of the generalized hydrodynamic model under strongly coupled conditions—i.e., in a regime where the system remains in a fluid state but exhibits significant interparticle correlations, with potential energy dominating over kinetic energy. In this paper, we extend the previous work by employing the same model to investigate the evolution of a dipole—represented by two counter-rotating Lamb–Oseen vortices—in an inhomogeneous medium. It is shown that the entire dynamics of a dipole is governed by the competition between the strength of transverse shear waves, which is proportional to the elastic strength of the viscoelastic background medium, and the circulation strength of the vortices in the dipole structure. The density inhomogeneity is introduced along the vertical direction, perpendicular to the direction of dipole motion, using both smooth and sharp cutoffs. The numerical simulations show that a higher circulation strength of a dipole and/or lower coupling strength of the background medium allows the dipole to survive longer and follow a more pronounced curved trajectory toward the high-density side. While the overall effects of circulation and coupling strength are similar in both densities, the resulting structure morphologies differ: in the smooth density case, the interface around the vortices gradually forms a mushroom-like shape, whereas in the sharp case, it forms a simple spiral envelope. These effects are visualized through two-dimensional simulations based on the incompressible generalized hydrodynamic model.