低密度泡沫金优化黑腔辐射驱动时变对称性研究

Time-dependent drive asymmetry is thought to make the significant contribution to implosion performance degradation in laser indirect driven inertial confinement fusion. Principal asymmetry source is SRS from the inner beams within the gas-filled hohlraums. However, the alternative hohlraum designs with lower gas fill pressures lead to drive asymmetry in the later phase of laser pulse, which is caused by plasma expanding from the hohlraum wall..We have found that, the velocity of plasma expanding from wall is lower in low density foam gold hohlraum compared to that in solid gold hohlraum. This characteristic would be benefit for propagation of inner cone, and improving the symmetry control in simple cylindrical hohlraums. American scientists also focus on this study. NISA plans to carry out relevant research in FY2019 – FY2020. In this project we intend to study the time-dependent drive symmetry in low density foam gold hohlraum..We attempt to get the relation between the movement of outer laser beam bubbles and wall density, and the dependence of the propagation of the inner laser beams on wall density. Furthermore, we try to establish the relation between time-dependent drive symmetry and wall density. Our research would be a useful supplement to the conventional hohlraum design, and would provide a novel option for improving hohlraum radiation source. It is our belief that the research would greatly facilitate the development of domestic ICF.

在间接驱动激光聚变研究中，黑腔辐射源的时变驱动不对称性已经成为制约点火成功的关键因素，而充气导致的内环激光背反份额增加是产生驱动不对称性的主要原因。由于腔壁等离子体膨胀，降低充气密度后的黑腔亦存在激光脉冲后期驱动不对称性的问题。.项目组前期研究成果表明，与固体金相比，低密度泡沫金等离子体膨胀速度较低，具有利于内环激光传输、改善驱动不对称性的重要潜力。目前，泡沫材料提升黑腔驱动对称性的研究已经被高度关注，美国NISA将其列入2019-2020年工作计划。.本项目拟率先开展泡沫金黑腔的辐射驱动时变对称性研究，通过模拟和实验相结合，判断其抑制抑制激光光斑移动的有效性，获得腔壁密度影响外环激光冕区等离子体运动和内环激光传输的基本规律；进一步通过数值模拟研究黑腔时变对称性与腔壁密度的依赖关系。本项目研究是常规黑腔设计的有益补充，为优化黑腔辐射源提供新的思路，并有助于推动国内研究达到国际领先水平。

黑腔辐射源的时变对称性调控，对于简接驱动惯性约束聚变研究极其重要。本项目研究泡沫金黑腔在等离子体膨胀、激光光斑膨胀、对称性调控等方面，相对于固体金黑腔的提升效果，是常规黑腔设计的有益补充。开展实验获得了黑腔内等离子体N带发光前沿运动速度，0.8g/cc的泡沫黑腔比固体金黑腔低20%，可有效降低外环激光bubble膨胀；实验获得高功率方波激光条件下，0.8 g/cc的金泡沫注入孔可降低注入孔等离子体膨胀速度，有利于激光注入；在~10ns的预脉冲激光条件下，泡沫腔壁光斑区运动速度比固体金腔壁降低~40%，可有效减缓光斑区运动速度，降低黑腔对称性调控难度。并结合IRAD三维视角因子程序和Multi一维辐射流体程序，评估基于十万焦耳激光装置，泡沫黑腔与固体黑腔的光斑膨胀、驱动不对称性和黑腔辐射温度等指标，表明泡沫黑腔具有优良的综合性能。