Structure Formation in PK-4 Compressional Experiments*

Complex plasmas can self-organize into various crystalline and liquid structural states, providing an exceptional platform for modeling fundamental processes relevant to materials science. Recent experiments conducted aboard the International Space Station in the Plasmakristall-4 (PK-4) facility have revealed that dusty plasmas in microgravity can form filamentary structures resembling electrorheological materials or liquid crystals resulting from an anisotropic interaction potential. Here we analyze video data from PK-4 experiments where, for fixed plasma conditions, the dust clouds were compressed with the goal of inducing a structural transition from a filamentary state into a crystalline lattice state. The goal is to assess the possibility of a triple point in microgravity dusty plasma – simultaneous existence of a hexagonal lattice, square lattice, and a disordered (liquid-like state). The existence of a triple point in dusty plasma was reported in 2023 through ground-based experiments [1]. To further understand how anisotropies in the interaction potential lead to the formation of different structures, we compare the experimental results to molecular dynamics simulations of dust and ions.

[1] Singh, S., et al. (2023). Physics of Plasmas, 30(12).