Spontaneous dust mass rotation in an unmagnetized dusty plasma

We report experimental observations of spontaneous mass rotation of a strongly coupled dusty plasma cloud without external magnetic field. The rotating structure resembles a convective cell pattern in the vertical plane and shows clear evidence of collective behavior as well as the influence of gravity on its angular speed. Vortex motion of dust cloud was followed right from the equilibrium state. It is identified that dust charge gradient perpendicular to gravity play important role in the generation of vortex motion. (C) 2003 Elsevier Science B.V. All rights reserved.