Self ordering to imposed ordering of dust -- a continuous spatial phase transition experiment in MDPX

TL;DR

This study investigates how dust particles in a plasma transition from self-organized hexagonal patterns to imposed ordering aligned with a conducting mesh when subjected to increasing magnetic fields, revealing a continuous phase transition.

Contribution

It provides experimental evidence of a continuous spatial phase transition from self ordering to imposed ordering in dusty plasma under magnetic influence, highlighting the role of electric potential structures.

Findings

Identification of a critical magnetic field for the transition

Observation of a shift from 6-fold to 4-fold symmetry

Quantification of dust phase changes

Abstract

Previous experiments conducted in the Magnetized Dusty Plasma eXperiment (MDPX) revealed an intriguing phenomenon first referred to as imposed ordering. This occurs when micron-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 4-fold symmetry of the boundary condition. It is hypothesized that beyond a certain magnetization, elongated electric potential structures emanating from the mesh drive the dust motion to reflect the mesh morphology, transitioning from a 6-fold self ordering to 4-fold 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.