Previous experiments conducted in the Magnetized Dusty Plasma eXperiment revealed an intriguing phenomenon first referred to as imposed ordering. This occurs when micrometer-sized dust particles become aligned with the geometry of a conducting mesh placed above the dust (at a distance much larger than the plasma Debye length or the ion–neutral or electron–neutral mean free paths) in the presence of a strong magnetic field perpendicular to the mesh. In this work, results of a transition experiment are presented wherein starting from a classical two-dimensional Coulomb crystal with hexagonal symmetry in an unmagnetized plasma (B=0 T), dust transitions to a state in which it flows along the geometry of a conducting mesh placed above it, mapping out the fourfold symmetry of the boundary condition. It is hypothesized that beyond a certain magnetization, elongated electric potential structures emanating from the mesh grow strong enough to drive the dust motion to reflect the mesh morphology, gradually transitioning from a sixfold self-ordering to fourfold imposed ordering. The various dust phases are quantified, and a critical value of magnetic field is identified in the transition experiment, indicating the onset of imposed ordering over the whole dust cloud.
Bachoti et al. (Mon,) studied this question.