CONFINEMENT AND STRUCTURE OF ELECTROSTATICALLY COUPLED DUST CLOUDS INA DIRECT-CURRENT PLASMA-SHEATH

Mechanisms for the confinement and the internal structure of an electr ostatically coupled dust cloud formed in a dc glow discharge have been investigated from a comparative viewpoint between experimental observ ations and a simple model. Two kinds of dust clouds with different int ernal structures are clearly observed, depending on the dispersion of the size distribution of dust particles. The dust cloud can be trapped only in the plasma-sheath boundary area, corresponding to the potenti al minimum region determined by gravitational and electrostatic forces in the cathode sheath. No dust particles were found deep inside of th e sheath, which is consistent with the analysis because the dust parti cles may be charged positively due to an extreme reduction of the elec tron density. The internal structure of the electrostatically coupled dust cloud was found to be arranged so that the total potential energy , including the repulsive Coulomb interaction among negative dust part icles, may become minimal. (C) 1998 American Institute of Physics. [S1 070-664X(98)01210-5].