Dynamic properties of crystallized fine-particle vortices

通过实验研究了直流和射频放电等离子体中电势结构和垂直磁场对微细颗粒涡旋形成的影响。首先，我们研究了悬浮电极上负偏压的小平板电极提供的非均匀电势分布驱动的微细颗粒涡旋的形成机理。实验结果表明，涡旋现象的出现取决于构成细粒云的细小粒子的数量。粒子在小电极边缘附近加速。随着颗粒数的增加，旋涡的旋转速度沿径向变化，出现剪切流。另一方面，当小电极电位为正时，细小颗粒会改变其流向小电极边缘的流动方向。如果用圆柱形电极代替平板，那么细小的颗粒就会被吸附到圆柱形电极中。这项技术用于去除尘埃等离子体中的细小颗粒。其次，我们研究了垂直磁场作用下细颗粒云旋转运动的驱动机制。我们发现，改变径向的密度或势分布控制着旋转方向。离子-反磁方向上的离子流动所产生的离子阻力在旋转中起着重要的作用。我们还观察到了细小粒子的自旋运动。结果表明，随着磁场的增大，自旋轴向磁场方向移动。

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.