  Two-dimensional microparticle 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 have shown that at a fixed
discharge power there are threshold pressures above and below which the
monolayer always crystallizes or melts, respectively. The melting is due to MCI
being triggered in the crystal monolayer, while the crystallization is due to
the suppression of MCI by neutral damping in the fluid monolayer. The
relationship between the discharge parameters and ion wake characteristics is
unknown. A molecular dynamics simulation of ion dynamics and dust charging is
used to self-consistently determine the dust charge and ion wake
characteristics for different experimental conditions. It is found that the ion
wake is strongly dependent on discharge pressure but not affected much by the
discharge power.
