Simple Hexagonal Coulomb Crystal near a Deformed Plasma Sheath Boundary in a Dusty Plasma

Simple hexagonal Coulomb crystals have been observed near a deformed plasma sheath boundary in a dusty plasma. It seems that particle rows, which are found in the direction perpendicular to an electrode in the Coulomb crystal, are formed due to not only Coulomb repulsive forces but also some attractive forces. In this study, experiments using the deformed sheath revealed that the rows were bent along the direction of electric fields and ion flows in a plasma. The result shows that sheath structures and shapes affect Coulomb crystal structures in dusty plasmas. In this paper, the formation of the particle rows are discussed, where balances of forces on particles in a dusty plasma are taken into account under the assumption that wake potentials related to ion flows exist in the sheath region.