The rotation of planar-2 to planar-12 dust clusters in an axial magnetic field

Dust clusters containing from one up to 12 particles arranged in a horizontal plane were formed in an inductively coupled rf plasma. When an axial magnetic field was applied to the dust cluster, the cluster rotated as a rigid body in the left-handed direction with respect to the field. The cluster rotation occurred at a magnetic field of tens of gauss in our experiment, which was two to three orders less than that used in previous experiments and that predicted by the models in the literature. In particular, the angular velocity dependence on magnetic field strength varied with number of particles in the cluster and with the structural configuration of the cluster. Other rotational properties such as cluster radius, angular momentum and threshold magnetic field were measured. The dependence of the radial confinement electric field on the magnetic field was also obtained. Finally, comparisons were made between our experimental results and various existing theoretical models. Possible explanations for angular velocity saturation and periodic pauses for the planar-2 configuration, which were observed in our experiments, are given.