On the origin of dust vortices in complex plasmas under microgravity conditions

Under microgravity conditions, microparticles in a radio-frequency plasma form an extended dust cloud. In such clouds, self-excited large-scale vortices are observed. New experimental observations are reported, which exhibit a simple double vortex structure or a more complex quadrupole-like topology. Modeling the fields of the main acting forces, namely, the electric field force and the ion drag force, and calculating the curl of these forces reveal their non-conservative character and the possible driving mechanism of the vortices. It is shown that the curl of the ion drag force and of the electric field force has opposite sign and the combination could thus lead to the complex structures, also found in the observations. (C) 2014 AIP Publishing LLC.