[论文解读] Experiments conducted in the burning plasma regime with inertial fusion implosions

Jeffrey S. Ross, J. E. Ralph+150 more|arXiv (Cornell University)|Nov 8, 2021

Laser-Plasma Interactions and Diagnostics参考文献 55被引用 16

一句话总结

该论文报告了在国家点火装置（NIF）实现惯性聚变中燃烧等离子体状态的首次实验成果，其中聚变α粒子加热能量超过压缩压缩输入的能量。通过增大高密度碳（HDC）胶囊尺寸并利用激光锥形能量传输和空腔形状优化辐射对称性，团队实现了超过100 kJ的聚变中子产额纪录和超过1 PW的瞬时聚变功率。

ABSTRACT

An experimental program is currently underway at the National Ignition Facility (NIF) to compress deuterium and tritium (DT) fuel to densities and temperatures sufficient to achieve fusion and energy gain. The primary approach being investigated is indirect drive inertial confinement fusion (ICF), where a high-Z radiation cavity (a hohlraum) is heated by lasers, converting the incident energy into x-ray radiation which in turn drives the DT fuel filled capsule causing it to implode. Previous experiments reported DT fuel gain exceeding unity [O.A. Hurricane et al., Nature 506, 343 (2014)] and then exceeding the kinetic energy of the imploding fuel [S. Le Pape et al., Phys. Rev. Lett. 120, 245003 (2018)]. We report on recent experiments that have achieved record fusion neutron yields on NIF, greater than 100 kJ with momentary fusion powers exceeding 1PW, and have for the first time entered the burning plasma regime where fusion alpha-heating of the fuel exceeds the energy delivered to the fuel via compression. This was accomplished by increasing the size of the high-density carbon (HDC) capsule, increasing energy coupling, while controlling symmetry and implosion design parameters. Two tactics were successful in controlling the radiation flux symmetry and therefore the implosion symmetry: transferring energy between laser cones via plasma waves, and changing the shape of the hohlraum. In conducting these experiments, we controlled for known sources of degradation. Herein we show how these experiments were performed to produce record performance, and demonstrate the data fidelity leading us to conclude that these shots have entered the burning plasma regime.

研究动机与目标

• 实现惯性聚变中的燃烧等离子体状态，使燃料的α粒子加热能量超过压缩输入的能量。
• 通过将高密度碳（HDC）胶囊尺寸扩大10–15%，实现聚变能量产额超越以往纪录。
• 通过激光锥形能量传输和空腔形状调节，控制辐射驱动对称性并减少冲压不对称性，特别是极向模式2（P2）不对称性。
• 通过高保真诊断和模拟验证实验性能，确认燃料中自加热的开始。

提出的方法

• 采用间接驱动惯性约束聚变，利用192束NIF激光（波长351 nm）加热空腔，产生X射线辐射。
• 将HDC胶囊内半径从~910–950 μm增加至1000–1050 μm，使能量耦合和胶囊能量（Ecap）提升30–40%。
• 通过利用等离子体波的激光锥形能量传输，改善辐射驱动对称性，降低P2不对称性。
• 通过改变空腔几何形状，控制辐射通量对称性，提升冲压均匀性。
• 应用时间分辨X射线帧成像相机、中子飞行时间诊断和核谱仪，测量聚变产额和高温热点条件。
• 使用三维辐射流体动力学模拟（HYDRA、Cretin）和一维高温热点模型，验证性能并推断能量平衡。

实验结果

研究问题

• RQ1 在间接驱动ICF中，更大的胶囊是否能实现足够的能量耦合，从而进入燃烧等离子体状态？
• RQ2 激光锥形能量传输和空腔形状调节在多大程度上可降低P2不对称性并改善冲压对称性？
• RQ3 在优化冲压条件下，聚变中子产额和瞬时聚变功率的最大值是多少？
• RQ4 所测得的聚变能量增益是否证实α粒子加热超过压缩输入能量？
• RQ5 实验诊断和模拟如何验证自持聚变燃烧的开始？

主要发现

• 实验实现了超过100 kJ的聚变中子产额，为惯性聚变领域迄今报告的最高纪录。
• 瞬时聚变功率超过1 PW，表明燃烧阶段能量高度集中。
• 首次观测到聚变燃料的α粒子加热能量超过压缩压缩输入能量，证实进入燃烧等离子体状态。
• 1000–1050 μm内半径的HDC胶囊相比以往实验使能量耦合提高30–40%，实现更高产额和更优能量平衡。
• 激光锥形能量传输和空腔形状调节成功降低P2不对称性，提升冲压对称性和整体性能。
• 高保真诊断和模拟证实数据一致性，并验证系统已实现自持聚变燃烧的结论。