Shock release from inertial confinement fusion (ICF) shells poses a great challenge to {} hydrodynamic equations, especially for describing materials composed of different ion species. This has been evidenced by a recent experiment [Haberberger {}, Phys. Rev. Lett. 123 , 235001 (2019)], in which low-density plasmas (10${}^{19}$ to 10${}^{20}$~cm${}^{-3}$) are measured to move far ahead of what radiation-hydrodynamic simulations predict. To understand such experimental observations, we have performed large-scale nonequilibrium molecular-dynamics simulations of shock release in polystyrene (CH) at experimental conditions. These simulations revealed that upon shock releasing from the back surface of a CH foil, hydrogen can {} out of the bulk of the foil due to its mass being lighter than carbon. This released hydrogen, exhibiting a much broader velocity distribution than carbon, forms low-density plasmas moving in nearly constant velocities ahead of the in-flight shell, which is in quantitative agreement with the experimental measurements. Such kinetic effect of species separation is currently missing in {} radiation-hydrodynamics codes for ICF simulations.

中文翻译：

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惯性约束聚变条件下聚苯乙烯释放冲击后的物种分离和氢流

惯性约束聚变（ICF）壳产生的冲击释放给{}流体力学方程式带来了巨大挑战，尤其是在描述由不同离子种类组成的材料时。最近的一项实验已证明了这一点[Haberberger {}，Phys。莱特牧师 123，235001（2019）]，其中低密度等离子体（10${}^{19}$ 至10${}^{20}$〜厘米${}^{-3}$）的测量远远超出了辐射流体动力学模拟的预测。为了解此类实验观察结果，我们在实验条件下进行了聚苯乙烯（CH）冲击释放的大规模非平衡分子动力学模拟。这些模拟表明，从CH箔的背面释放冲击后，氢可以{}离开箔的主体，因为它的质量比碳轻。释放出的氢比碳具有更宽的速度分布，形成了低密度等离子体，该低密度等离子体以几乎恒定的速度移动到飞行中的机壳之前，这与实验测量结果定量一致。{} ICF模拟的辐射-流体动力学代码目前缺少物种分离的这种动力学效应。