Alignment and instability of dust crystals in plasmas

Charged dust particulates, forming a layered crystal in the electrode sheath of a rf discharge, are known to show vertical alignment and an onset of characteristic oscillations below a threshold of neutral gas density. Here forces on the particulates due to the formation of positive space-charge clouds below the dust particles are calculated from Monte Carlo calculations of the ion motion in the sheath. The forces are shown to be attractive and nonreciprocal for the different crystal layers; From the Monte Carlo results an analytical lattice model is derived that quantitatively explains the experimental findings.