Plasma potential and grain charges in a dust cloud embedded in a plasma

Abstract

We have calculated the plasma potential and dust potential throughout the border region of semiinfinite dust clouds embedded in a plasma. A relevant ordering parameter is P = (N _d0/N₀)a_μ (interior dust density/exterior plasma density) × dust radius (in microns). For comparatively high dust densities (P > 10⁻³) the cloud potential is high, screening out electrons, with low interior dust charges as a result. For decreasing P the cloud potential becomes less, with a corresponding increase in the dust charges. At P < 10⁻⁵ the cloud potential is practically zero and the dust particles have their maximum charge which is identical to that of a single dust particle in a plasma. For diffuse dust border regions with density scale length H ≫ λ_D (Debye length), the deviations from charge neutrality are small. When H ≲ λ_D, large deviations from charge neutrality occur in the border region and also some penetration of electric fields inside the border region.