The trap of particles in plasma sheath

The traps of isolated dust particles under the action of electrostatic, gravitational, ion-drag, and neutral collision forces are investigated near the boundary of a dusty plasma. It is shown that in the lower sheath (above the lower electrode) the particle traps can exist only for the negatively charged particles. The positions of trapped particle are determined by grain size and forces on it and there are upper and lower critical values for the trapped particle. In the upper sheath (under the upper electrode) there is balance force for the positively charged particles but it is not a stable balance. Still negatively charged particles can be trapped in the upper sheath. In addition, it was shown that two sized grains are trapped in the same position. (C) 1999 American Institute of Physics. [S1070-664X(99)00105-6].