Dynamic properties of crystallized fine-particle vortices

The effects of potential structure and vertical magnetic field on the vortex formation of fine particles are investigated in dc and rf discharge plasmas experimentally. First, we investigate the formation mechanism of fine-particle vortex driven by inhomogeneous potential profile provided by a small plate electrode biased negatively that is placed on a levitation electrode. It is observed that the appearance of vortex phenomena depends on the number of fine particles constituting the fine-particle cloud. The particles are accelerated near the edge of the small electrode. The rotation speed of the vortex varies in radial direction and a shear flow appears with increasing the particle number. On the other hand, when the small electrode potential becomes positive, the fine particles change their flow direction towards the edges of the small electrode. If a cylindrical electrode is used instead of the plate, then the fine particles are absorbed into the cylindrical electrode. This technique is used for fine-particle removal from the dusty plasma. Secondary, we have investigated the driving mechanism of a rotational motion of fine-particle cloud in the presence of vertical magnetic field. We find that changing either density or potential profile in radial direction controls the rotational direction. The ion drag force due to the ion flow in ion-diamagnetic direction takes an important role of the rotation. We also observe a spin motion of fine particle. It is found that the spin axis turns to the magnetic field direction with increasing the magnetic field.