Vortex Formation and Its Interaction in Real Plasmas

利用定向朗缪尔探针离子饱和电流的对称性原理，提出了一种测量流速的新方法。得到了离子流速与探针信号之间的一般关系。利用定向朗缪尔探针和发射探针测量ExB的旋转速度，证明了磁场对探针电流的影响可以消除，定向探针法测量流速在磁化等离子体中是有效的，利用这种方法测量了速度场，并通过构造涡度分布来考察等离子体中涡旋的形成。发现了两种在等离子体中从未观察到的涡旋：一种是Burgers涡旋（等离子体空穴）;第二类涡旋为三极涡旋，其旋转方向与ExB漂移方向相反。研究发现，背景中性粒子的强烈不均匀性导致中性流，中性流的动量通过电荷交换相互作用输运到离子中，从而产生一个比内部径向电场更强的净径向力。三极涡旋是第一次观察到的涡旋在等离子体中所造成的机制以外ExB漂移。

A new method of measuring flow velocity has been developed with the symmetry principle on ion saturation current of a directional Langmuir probe. The general relation between ion flow velocity and probe signal has been obtained. Measuring ExB rotation velocity by a directional Langmuir probe and an emissive probe, we have demonstrated that the effect of magnetic field on the probe current can be eliminated, and that the directional probe method for flow velocity measurements is valid in magnetized plasmas.Using this method, we have measured velocity fields, and examined vortex formation in plasmas, by constructing the vorticity distribution. Two types of vortex, which have never been observed in plasmas, have been found. One is Burgers vortex (plasma hole). This vortex appears with a density cavity in its center and viscosity of the plasma exhibits anomaly.The second type of vortex is a tripolar vortex, which rotates in the inverse direction of ExB drift. It is found that strong inhomogeneity in the back ground neutrals causes a neutral flow, whose momentum is transported into the ions by the charge exchange interactions, and then produces a net radial force stronger than the internal radial electric field. The tripolar vortex is the first observation of vortex in a plasma caused by a mechanism other than ExB drift.