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

Vortex motion of the dust in a dusty plasma is shown to result because non-parallelism of the ion density gradient and the gradient of the magnitude of the ion ambipolar velocity cause the ion drag force on dust grains to be non-conservative. Dust grain poloidal vortices consistent with the model predictions are experimentally observed, and the vortices change character with imposed changes in the ion temperature profile as predicted. For a certain ion temperature profile, two adjacent corotating poloidal vortices have a well-defined X-point analogous to the X-point in magnetic reconnection. (C) 2016 AIP Publishing LLC.