Modeling of self-excited dust vortices in complex plasmas under microgravity

Abstract

A two-dimensional hydrodynamic model for a dusty argon plasma in which the plasma and dust parameters are solved self-consistently has been supplemented with a separate dust particle tracing module to study the behavior of dust vortices. These coherent vortices appear in plasma crystal experiments performed under microgravity conditions. The nonconservative total force exerted by the discharge on the dust particles is responsible for the generation of the vortices. The contribution of the thermophoretic force driven by the gas temperature gradient plays an insignificant role in the generation of the vortices, even when the gas heating via the dust particles is taken into account. The forces related to the electric field, including the ion drag force, are dominant.

Simulating the dynamics of complex plasmas

“…Charge fluctuations are not included in our model, and the vortices form nevertheless. In contrast to [11], in our model, we do not only find one stable position in the chamber midplane, but a stable circle around the void. If the neutral gas pressure is low enough, vortices appear when two or more layers of microparticles are present and their positions are only slightly removed from the equilibrium line.…”

“…8 is of the order of 1 mm/s. Akdim and Goedheer [11] modeled vortices in complex plasmas using tracer particles in a fluid simulation. They explain the formation of the vortices as follows: There is one equilibrium position in the midplane of the chamber where the confinement force equals the ion drag force.…”

Collective Effects in Vortex Movements in Complex Plasmas

“…The magnitude of the curl of the vector field is largest near the edges of the microparticle cloud, on the outside of the equilibrium line, whereas it nearly vanishes on the inside of the equilibrium line and in the mid-plane of the simulation box. This qualitatively confirms the basic result of Akdim and Goedheer [22]: The vortices can be caused by a non-vanishing curl of the plasma force (see also [43]). …”

Vortex motion of dust particles due to non-conservative ion drag force in a plasma

“…11,12 However, the cause of vortex flows remains controversial. Akdim and Goedheer 13 and Schwabe and Graves 14 postulated that a non-zero curl of the total force exerted on dust particles causes vortex flow; Shimizu et al 10 argued that dust particle vortex flow is induced by vortex neutral gas flow caused by the temperature gradient between two electrodes; and Fortov et al 15 claimed that dust particle vortex flow results when the gradient of dust charge is not parallel to non-electrostatic forces such as the ion drag force and gravitational force.…”