Hughto J, Schneider A S, Horowitz C J, Berry D K
Department of Physics, Indiana University, Bloomington, Indiana 47405, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Dec;82(6 Pt 2):066401. doi: 10.1103/PhysRevE.82.066401. Epub 2010 Dec 1.
Sedimentation of the neutron rich isotope 22Ne may be an important source of gravitational energy during the cooling of white dwarf stars. This depends on the diffusion constant for 22Ne in strongly coupled plasma mixtures. We calculate self-diffusion constants D(i) from molecular dynamics simulations of carbon, oxygen, and neon mixtures. We find that D(i) in a mixture does not differ greatly from earlier one component plasma results. For strong coupling (coulomb parameter Γ> few), D(i) has a modest dependence on the charge Z(i) of the ion species, D(i)∝Z(i)(-2/3). However, D(i) depends more strongly on Z(i) for weak coupling (smaller Γ). We conclude that the self-diffusion constant D(Ne) for 22Ne in carbon, oxygen, and neon plasma mixtures is accurately known so that uncertainties in D(Ne) should be unimportant for simulations of white dwarf cooling.
富含中子的同位素(^{22}Ne)的沉降可能是白矮星冷却过程中引力能的一个重要来源。这取决于(^{22}Ne)在强耦合等离子体混合物中的扩散常数。我们通过对碳、氧和氖混合物的分子动力学模拟来计算自扩散常数(D(i))。我们发现混合物中的(D(i))与早期单一组分等离子体的结果差别不大。对于强耦合（库仑参数(\Gamma\gt)几个），(D(i))对离子种类的电荷(Z(i))有适度的依赖性，(D(i)\propto Z(i)^{(-2/3)})。然而，对于弱耦合（较小的(\Gamma)），(D(i))对(Z(i))的依赖性更强。我们得出结论，碳、氧和氖等离子体混合物中(^{22}Ne)的自扩散常数(D(Ne))已被准确知晓，因此(D(Ne))的不确定性对于白矮星冷却模拟来说应该并不重要。
