Dust chain formation in microgravity complex plasma*

The one-dimensional (1D) dusty chain is the simplest stable complex plasma structure that exhibits a variety of fundamental interactions and at the same time allows for easy experimental tracking and elegant theoretical modeling. We investigate string formation utilizing video data from the Plasmakristal-4 (PK-4) facility on the International Space Station. In the absence of gravity, a variety of 1D dust structures form in the bulk of the plasma, where phenomena specific to self-ordering become increasingly important. The possible mechanisms guiding such 1D self-ordering can be organized into three groups: 1) ion wake-mediated interaction (symmetric and asymmetric), 2) dust particle effects (grain polarization, temperature/charge fluctuations, and demixing), and 3) system-induced interactions (discharge striations, shear flow, and thermal gradient effects). We first present a theoretical formulation of each mechanism and then identify the system parameter space where each effect is observable under microgravity conditions. Finally, the theoretical predictions are tested against the experimental data from the PK-4 laboratory.