Toroidal Dust Clouds and Voids in a Magnetized Anodic Plasma

Dust particles confined in a magnetized anodic plasma can form different cloud shapes. In a certain parameter regime, torus-shaped dust clouds with a dust-free region (void) in the center are found. One can observe that most of the particles perform a rotational motion about the major axis of the torus. In order to understand the responsible mechanism, a model was developed to describe the confinement of dust particles by means of a force balance of electric field force and ion drag force derived from electric measurements of the plasma potential and the plasma density. Furthermore, a condition for the onset of the particle rotation and, with it, the formation of a torus-shaped cloud is developed. It is also possible to estimate the rotation velocity of the particles. The resulting values are compared with the data observed by particle image velocimetry.