Analytic and simulation studies of dust grain interaction and structuring

For dust grains in stationary plasma, a quantitative assessment is made of the effect of centrifugal potential barriers on ion trajectories near a gra in. It is shown that in most situations of interest the barriers are weak a nd only marginally affect the validity of the orbital-motion-limited (OML) theory. The OML theory is then used to show that the electrostatic interact ion between grains is always repulsive. The ion-shadowing force is calculat ed, and it is shown that this force can lead to a weak net attraction betwe en grains at long range, under certain conditions with large grains, dense plasma, and/or low gas pressure. For grains in streaming plasma at or near the sheath, it is shown that nonlinear effects are weak and the grains can be represented as dressed particles interacting via the dynamically shielde d Coulomb interaction, which includes wakefields, Landau damping, and colli sional damping. The Dynamically Shielded Dust (DSD) simulation code, which is based on this model, is described and a simulation is shown for strongly coupled grains in flowing plasma. The simulation shows ordering of the gra ins into rigid strings aligned with the ion flow, and looser glass-like org anization of the strings in the transverse plane. The presence of strings w ith odd and even numbers of grains results in stratification of the grains into planes with an alternating structure.