Forming Ordered Structures with Charged Dust in the Presence of Ion Wakes*

Charged dust grains have been experimentally observed to form ordered structures in complex ('dusty') plasma, including single chains that align with the ion flow direction, zigzags or double chains, and helices formed by multiple parallel chains surrounding a single axis. The self-organization of dust grains into these structures requires a balance between confinement forces and interparticle interactions among the charged species present in a dusty plasma. The formation of ion wakes (regions of high charge density downstream from the dust grains) alters the interaction between charged dust grains, while the relative positions of charged dust within a structure affect the formation of the ion wakes. As a result, understanding ion wake morphology during the transitions from one stable dust structure to another is a critical component for describing the self-organization of dust grains. In order to develop a model capable of predicting the formation of various structures, the present study systematically analyzes the formation of ion wakes in the presence of various orientations of stationary dust using a molecular dynamics simulation that models ion and dust dynamics and dust charging. The results are then used to determine the variation in radial and axial confinement forces needed to promote the self-organization and transition between these charged dust structures.