Experimental achievement and signatures of ignition at the National Ignition Facility

An inertial fusion implosion on the National Ignition Facility, conducted on August 8, 2021 (N210808), recently produced more than a megajoule of fusion yield and passed Lawson’s criterion for ignition [Phys. Rev. Lett. 129, 075001 (2022)]. We describe the experimental improvements that enabled N210808 and present the first experimental measurements from an igniting plasma in the laboratory. Ignition metrics like the product of hot-spot energy and pressure squared, in the absence of self-heating, increased by ∼35%, leading to record values and an enhancement from previous experiments in the hot-spot energy (∼3×), pressure (∼2×), and mass (∼2×). These results are consistent with self-heating dominating other power balance terms. The burn rate increases by an order of magnitude after peak compression, and the hot-spot conditions show clear evidence for burn propagation into the dense fuel surrounding the hot spot. These novel dynamics and thermodynamic properties have never been observed on prior inertial fusion experiments.2021年8月8日于国家点火装置（National Ignition Facility）开展的编号为N210808的惯性约束聚变（inertial fusion）内爆实验，近期实现了超过1兆焦的聚变产额，并满足了点火的劳逊判据（Lawson's criterion）[《物理评论快报》（Physical Review Letters）129, 075001 (2022)]。本文阐述了支撑N210808实验的各项实验改进，并首次报道了实验室中点火等离子体的实验测量结果。在不考虑自加热（self-heating）的前提下，热斑（hot-spot）能量与压强平方的乘积这类点火参数提升了约35%，创下了纪录值；相较于此前实验，热斑能量（约3倍）、压强（约2倍）与燃料质量（约2倍）均实现了显著提升。上述结果与自加热主导功率平衡各项分量的结论一致。峰值压缩（peak compression）阶段过后，燃烧速率（burn rate）提升了一个数量级，且热斑环境清晰展现出燃烧向热斑周围稠密燃料传播的明确证据。此类全新的动力学与热力学特性，在以往的惯性约束聚变实验中从未被观测到。