Formation of a boundary-free dust cluster in a low-pressure gas-discharge plasma.

An attraction between negatively charged micron-sized plastic particles was observed in the bulk of a low-pressure gas-discharge plasma under microgravity conditions. This attraction had led to the formation of a boundary-free dust cluster, containing one big central particle with a radius of about 6 microm and about 30 1 microm-sized particles situated on a sphere with a radius of 190 microm and with the big particle in the center. The stability of this boundary-free dust cluster was possible due to its confinement by the plasma flux on the central dust particle.