Impact of ion wakes on two-dimensional dust structure stability

Two-dimensional dust crystals can be formed in the sheath of a gas discharge plasma. Ions from the bulk plasma are accelerated in the sheath electric field, flowing past the grains to create a positive ion wake downstream from the grains. Interaction between the ion wake and neighboring grains creates additional coupling between oscillation modes and can trigger mode-coupling instability (MCI). Recent experiments show that for a given microparticle monolayer at a fixed discharge power there exist two threshold pressures above and below which the monolayer always crystallizes or melts due to the MCI, respectively. Between these pressures, the microparticle monolayer can be either in a fluid or crystalline phase. In this work, a molecular dynamics simulation of the ions and dust charging is used to self-consistently determine the dust charge and ion wake characteristics for different experimental conditions. An iterative approach is used to determine plasma parameters which optimizes a balance between the electric and gravitational field forces on the dust grain and the ion flow speed. This data is then utilized in an N-body model of dust dynamics using a dynamic point charge model to study the role of ion wakes in triggering the mode coupling instability.