Influence of gas pressure on the structure and dynamics of dust rotation in magnetized dusty plasmas

The structure and dynamics of dust rotation under a magnetic field at different gas pressures in the sheath of a radio-frequency discharge are investigated in this paper. The influence of gas pressure on the rotational properties of the dust particles located in different layers is studied in detail. Both rigid rotation (all the dust particles move with a constant angular velocity) and sheared rotation (the angular velocity of the dust particles has a radial distribution) of the dust particles induced by a magnetic field are observed. With increasing gas pressure, the angular velocity of the rotating dust particles in all layers decreases. Under specific experimental conditions, the angular velocity of the dust particles in the lower layer is lower than that of the dust particles in the upper layers. With increasing gas pressure, dust particles in the lower layer stop rotating earlier than those in the upper layers. At a critical (high) gas pressure, dust particles in the lower layers also reverse their rotation direction earlier than those in the upper layers. Within the same dust layer, particles located in the inner region stop rotating and reverse their rotation direction earlier than those in the outer region. At a sufficiently high angular velocity, a void (dust-free region) is formed in the dust cloud, leaving the dust particles rotating in a layer at the system edge. When the gas pressure becomes too high, the voids can be destroyed, and the dust particles are redistributed in the dust cloud. Finally, a 3D spindle-shaped configuration of the dust cloud in the plasma sheath can also be obtained. The experimental results are discussed in detail.