Dynamics of fine particles in magnetized plasmas

Here are presented experiments on fine particles levitating in low-pressure weakly ionized plasmas under a vertical magnetic field. The magnetic field is useful to provide a vertically long cylindrical column of fine-particle clouds, yielding even string-shaped vertically aligned fine particles, und er the double-plasma configuration. Measurements show that fine-particle cl ouds rotate in the azimuthal direction on the horizontal plane even in such a weak magnetic field that positive ions are slightly magnetized. With an increase of the magnetic field, the rotation speed increases, being followe d by subsequent saturation. The rotation speed and direction can be control led by varying radial plasma potential and/or density profiles. The rotatio n is induced under the condition that the interparticle distance is small e nough for the strong Coulomb coupling among fine particles. A mechanism of the rotation could be explained by effects of ion motions on fine particles , which are modified in the presence of the vertical magnetic field. (C) 20 01 American Institute of Physics.