Interactions between dust grains in a dusty plasma

TLDR

Dust grains in plasma acquire large negative charges and can form a strongly coupled system. In a stationary plasma, the electrostatic potential around a grain is described by OML theory with ion absorption, while in a streaming plasma each grain generates a wake‑field potential via linear response that attracts other grains behind it. The grain–grain interaction is repulsive at all ranges with a long‑range r⁻² decay, but nonlinear and wake‑field effects introduce additional attractive forces—ion‑impact momentum deposition and shadowing can produce weak long‑range attraction, while trapped‑ion effects become important at high density yet remain uncalculated.

Abstract

Dust grains in plasma acquire a large negative charge, and can constitute a strongly coupled system. If the plasma is stationary, the plasma-mediated electrostatic potential around a single grain can be calculated by orbital-motion-limited (OML) theory, including ion absorption at the grain surface. This potential is repulsive at all ranges, and falls off as r−2 at long range. Nonlinear modifications occur when there are several grains, but the interaction is still repulsive. If the plasma is streaming by the grains, each grain generates a wake field potential which can be calculated via linear response theory, and which attracts other grains to stationary points behind the grain. There is in addition an attractive force between grains, due to ion-impact momentum deposition. In certain parameter regimes, this “shadowing” force can yield a weak net attraction at long range. Trapped-ion effects are significant at high plasma density, but have not yet been calculated.