Dynamic properties of crystallized fine-particle vortices

实验研究了直流和射频放电等离子体中电位结构和垂直磁场对细粒子涡旋形成的影响。首先，我们研究了悬浮电极上的负偏小极板电极提供的不均匀电位分布驱动的细颗粒涡旋的形成机制。观察到，涡旋现象的出现取决于构成细粒子云的细粒子的数量。粒子在小电极的边缘附近加速。随着颗粒数的增加，涡旋的旋转速度在径向上发生变化，并出现剪切流动。另一方面，当小电极电位变为正时，细颗粒改变流向小电极边缘。如果使用圆柱形电极代替平板，那么细颗粒被吸收到圆柱形电极中。这项技术用于从尘埃等离子体中去除细颗粒。其次，我们研究了垂直磁场存在下细粒子云旋转运动的驱动机制。我们发现，在径向上改变密度或势分布可以控制旋转方向。离子沿离子反磁方向流动所产生的离子阻力对旋转起着重要作用。我们还观察到细粒子的自旋运动。结果表明，随着磁场的增大，自旋轴向磁场方向转变。

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.