激光驱动等离子体向腔相关背景气体膨胀的测量
Measurements of Laser-Driven Plasma Expansion into Hohlraum-Relevant Background Gas
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中文总结 AI 辅助
该研究在OMEGA EP装置上开展实验，测量激光驱动铜等离子体向腔相关氦气的膨胀，对比Gorgon与HYDRA模拟结果发现二者对膨胀速率的预测存在20-50%的偏差，为腔等离子体建模提供了约束。
中文摘要 AI 辅助
在OMEGA EP激光装置上设计并开展实验，研究等离子体向腔相关气体填充（0.3-0.6毫克/立方厘米的氦气）的膨胀，为研究腔壁喷溅、非局域输运和磁化等离子体效应提供替代平台。我们观察到激光驱动铜等离子体向低原子序数背景气体膨胀时形成的清晰密度特征和丝状结构。阴影成像随时间分辨出尖锐的密度特征，并揭示激光光斑区域的细尺度丝状结构，在箔表面附近具有10-100微米的特征横向尺度。质子成像对路径积分的磁场和整个气泡体积内的密度调制敏感。我们提取两种气体压力下气泡随时间的膨胀情况：350 psi（产生0.3毫克/立方厘米等效条件）和700 psi（产生0.6毫克/立方厘米等效条件），并将测得的传播情况与Gorgon和HYDRA磁流体动力学模拟结果进行比较。尽管两种代码都能较好再现气泡的大尺度形状，但与1-3纳秒间的实验观测相比，随时间变化的膨胀速率存在显著差异（快20-50%），这导致后期气泡尺寸的差异逐渐增大。对气泡膨胀和小尺度结构演化的光学测量，为腔相关等离子体中的Biermann电池场产生、热输运和不稳定性增长提供了额外约束，以确保对气体填充腔的准确预测建模。
英文摘要
Experiments at the OMEGA EP laser facility were designed and executed to study plasma expansion into hohlraum-relevant gas fills (0.3-0.6 mg/cc of helium), providing a surrogate platform for investigating hohlraum wall blow-off, non-local transport, and magnetized plasma effects. We observe well-defined density features and filamentary structures as laser-driven copper plasma expands into a low-Z background gas. Shadowgraphy resolves sharp density features over time and reveals fine-scale filamentation in the laser spot region with characteristic transverse scales of 10-100 microns near the foil surface. Proton radiography provides sensitivity to path-integrated magnetic fields and density modulations throughout the bubble volume. We extract the bubble expansion as a function of time for two gas pressures, 350 psi (producing 0.3 mg/cc equivalent conditions) and 700 psi (0.6 mg/cc equivalent conditions), and compare the measured propagation to magnetohydrodynamic simulations performed with Gorgon and HYDRA. While the large-scale shape of the bubble is well reproduced by both codes, the time-dependent expansion rate shows significant discrepancies (20-50% faster) compared to experimental observations between 1 and 3 ns. This leads to increasingly larger differences in bubble sizes at later times. The optical measurements of bubble expansion and evolution of small-scale structures point to additional constraints required for Biermann-battery field generation, thermal transport, and instability growth in hohlraum-relevant plasmas, to ensure accurate, predictive modeling of gas-filled hohlraums.
