Structure of strongly coupled multicomponent plasmas

We investigate the short-range structure in strongly coupled fluidlike plasmas using the hypernetted chain approach generalized to multicomponent systems. Good agreement with numerical simulations validates this method for the parameters considered. We found a strong mutual impact on the spatial arrangement for systems with multiple ion species which is most clearly pronounced in the static structure factor. Quantum pseudopotentials were used to mimic diffraction and exchange effects in dense electron-ion systems. We demonstrate that the different kinds of pseudopotentials proposed lead to large differences in both the pair distributions and structure factors. Large discrepancies were also found in the predicted ion feature of the x-ray scattering signal, illustrating the need for comparison with full quantum calculations or experimental verification.

Figure 1

(Color online) (a) Partial pair distributions for a CH plasma with $n_H=n_C=2.5\times {10}^{23}{\text{cm}}^{-3}$ and $T=2\times {10}^4\text{K}$. The hydrogen and carbon ions are fully and fourfold ionized, respectively. For comparison, the dashed line, labeled $Z=1$, shows results for an isolated hydrogen plasma under the same conditions. (b) Static structure factors for the same CH plasma.

Figure 2

(Color online) (a) Partial pair distributions (dotted) for a gold plasma with $n_i={10}^{24}{\text{cm}}^{-3}$, $T={10}^4\text{K}$, and ion charge states of $Z=1$ and $Z=2$ (equally distributed). The solid line shows the averaged pair distribution (11) and the dashed line the results of a one-component calculation with $\overline{Z}=1.5$. (b) Same as (a) for the static structure factor.

Figure 3

(Color online) (a) Electron-ion (upper triple) and ion-ion (lower triple) pair distributions for a plasma with $n_i={10}^{22}{\text{cm}}^{-3}$, $Z=1$, and $T=4.5\times {10}^4\text{K}$. Different quantum pseudopotentials are used for the $e\text{−}i$ and $e\text{−}e$ interactions as labeled. In the case of the KK potential (15), the $e\text{−}e$ interaction is described by the Deutsch potential (14). $i\text{−}i$ interactions are always described by the Coulomb potential. (b) Same as (a) for the static structure factors.

Figure 4

(Color online) Comparison of the HNC results with molecular dynamics simulations for a plasma that contains different ion species: ${\text{Xe}}^{11+}$ with $n_i=7.5\times {10}^{23}{\text{cm}}^{-3}$, ${\text{Xe}}^{10+}$ with $n_i=3\times {10}^{23}{\text{cm}}^{-3}$, ${\text{Ar}}^{8+}$ with $n_i=5\times {10}^{22}{\text{cm}}^{-3}$, and ${\text{He}}^{\text{2+}}$ with $n_i=5\times {10}^{23}{\text{cm}}^{-3}$. The plasma temperature is $T=2.5\times {10}^6\text{K}$. Shown are the functions $g_{ee}$ and $g_{ei}$ and the partial pair distributions for like ions, $g_{aa}$. The pair interactions are modeled by the Deutsch potential (14).

Figure 5

(Color online) Partial structure factors for an aluminum plasma with $n_i=2.7\times {10}^{22}{\text{cm}}^{-3}$, $Z=3$, and $T=1.5\times {10}^5\text{K}$. The line styles correspond to different approximations for the $e\text{−}e$ exchange potential; the diffraction part and the $e\text{−}i$ interactions are described by the Deutsch potential (14) (Coulomb for $i\text{−}i$ interactions).

Figure 6

(Color online) Comparison of the results from a multicomponent HNC approach using different quantum pseudopotentials for the conditions of recent x-ray scattering experiments [7] on beryllium with $n_i=1.23\times {10}^{23}{\text{cm}}^{-3}$, $T=1.39\times {10}^5\text{K}$, and $Z=2.2$. (a) Partial pair distributions and (b) structure factors.