Effect of Nonlinear Screening on a Complex Plasma Phase State

Applicability limit of the well-known phase diagram of dusty plasmas in κ-Γ plane (κ is structural parameter and Γ is parameter of Coulomb nonideality) is under discussion. Existence of extensive domains with violation of plasma thermodynamic stability conditions (i.e., with negative isothermal compressibility) was also claimed if one uses well-known nonideal equations of state by (Hamaguchi S. et al., Phys. Rev. E, 1997) and (Khrapak S. et al., Phys. Rev. E, 2014). This paper is devoted to analysis of a range of applicability for basic assumption in Hamaguchi's phase diagram, i.e., linearized (Debye) screening of macroions by microions, which leads to the Yukawa form for effective interactions between macroions. Parameters of nonlinear screening for macroions were calculated within differential Poisson-Boltzmann equation. Two effects were revealed as a result of such calculations: 1) decomposition of all micro-ions onto two subclasses, free and bound ones, and 2) significant reduction of effective charge Z* of initial bare macroion Z under nonlinear screening by small high-density envelope of bound ions. This effect leads to a renormalization of initial Γ and κ into Γ* and κ* (Γ* <; Γ, κ* <; κ). The main physical assumption is phase states of complex plasma under nonlinear screening, which are still the same as on the initial phase diagram, but in κ*-Γ* plane instead of κ-Γ one. Corresponding calculated shifts of phase states are discussed and illustrated.