Non‐linear screening and phase states of a complex plasma

Abstract

The applicability limit of the well‐known phase diagram of complex plasmas in the κ–Γ plane (κ is the structural parameter, Γ is the coupling parameter) is under discussion. The present work is devoted to the analysis of the range of applicability of a basic assumption in the initial phase diagram, that is, linearized (Debye) screening of macro‐ions by micro‐ions, which leads to the Yukawa form of effective interactions between macro‐ions. Parameters of non‐linear screening for macro‐ions were calculated within the direct Poisson–Boltzmann approximation in an averaged Wigner–Seitz cell. Two effects were revealed as a result of such calculations: (a) decomposition of all micro‐ions into two subclasses, free and bound ones, and (b) significant reduction of the effective charge Z* of initial bare macro‐ion Z under non‐linear screening by the small high‐density envelope of bound micro‐ions. This effect leads to a re‐normalization of initial Γ and κ into Γ* and κ* (Γ* < Γ, κ* < κ). It is assumed that the phase states of a complex plasma under non‐linear screening are still the same as in the initial phase diagram, but in κ*–Γ* plane instead of the κ–Γ one. The corresponding calculated shifts of the phase states are discussed and illustrated.