Structure Formation in PK-4 Microgravity Dusty Plasma 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 dust-dust interaction potential. Here we analyze video data from two types of PK-4 experiments. In the first, we investigate how changes in the formation and stability of filamentary structure in different pressure and current plasma conditions. In the second, we study the formation of crystalline structure for fixed plasma conditions but changing dust densities through dust cloud compression. The goal is to assess the coexistence of multiple structural states in microgravity dusty plasma – simultaneous existence of a hexagonal lattice, square lattice, and a disordered (liquid-like state). To determine the structure types, we calculate the bond-order parameter for different symmetries. We further quantify disorder concentration as the deviation from the average interparticle separation in each type of structure, which allows us to assess the rigidity of the domains.