The first laser–plasma interaction experiment using lasers of eight beams grouped into one octad has been conducted on the Shenguang Octopus facility. Although each beam intensity is below its individual threshold for stimulated Brillouin backscattering (SBS), collective behaviors are excited to enhance the octad SBS. In particular, when two-color/cone lasers with wavelength separation 0.3 nm are used, the backward SBS reflectivities show novel behavior in which beams of longer wavelength achieve higher SBS gain. This property of SBS can be attributed to the rotation of the wave vectors of common ion acoustic waves due to the competition of detunings between geometrical angle and wavelength separation. This mechanism is confirmed using massively parallel supercomputer simulations with the three-dimensional laser–plasma interaction code LAP3D.

The results of a commissioning experiment on the SILEX-Ⅱ laser facility (formerly known as CAEP-PW) are reported. SILEX-Ⅱ is a complete optical parametric chirped-pulse amplification laser facility. The peak power reached about 1 PW in a 30 fs pulse duration during the experiment. The laser contrast was better than 10¹⁰ at 20 ps ahead of the main pulse. In the basic laser foil target interaction, a set of experimental data were collected, including spatially resolved x-ray emission, the image of the coherent transition radiation, the harmonic spectra in the direction of reflection, the energy spectra and beam profile of accelerated protons, hot-electron spectra, and transmitted laser energy fraction and spatial distribution. The experimental results show that the laser intensity reached 5 × 10²⁰ W/cm² within a 5.8 µm focus (FWHM). Significant laser transmission did not occur when the thickness of the CH foil was equal to or greater than 50 nm. The maximum energy of the accelerated protons in the target normal direction was roughly unchanged when the target thickness varied between 50 nm and 15 µm. The maximum proton energy via the target normal sheath field acceleration mechanism was about 21 MeV. We expect the on-target laser intensity to reach 10²² W/cm² in the near future, after optimization of the laser focus and upgrade of the laser power to 3 PW.

为研究多色非相干激光入射ICF黑腔的受激布里渊散射（SBS）和受激拉曼散射（SRS）发展情况，建立了一维受激散射稳态谱分析模型，并发展了相应的数值模拟程序。分析了不同频率激光激发的受激散射光通过共用等离子体波耦合的物理图像以及影响背散光谱的物理因素。针对波长差0.3 nm的等强度双色光入射封底金腔的SBS进行了模拟分析，结果表明：采用双色光有效抑制了SBS；SBS光谱劈裂成间距为0.3 nm的两个峰；波长较长的入射光对应的SBS光获得了较大的增益；如果固定激光总强度和总带宽，则存在抑制SBS的最优光束数目。

动理学效应的研究是近年来激光惯性约束聚变领域的研究热点，有助于理解实验结果和传统流体模拟之间的偏差。间接驱动黑腔中等离子体的温度、密度跨越多个量级且靶丸组分复杂，在局域的高温低密度区域，粒子的非平衡效应开始变得显著，可能会间接影响内爆性能。对ICF领域动理学效应的概念和部分进展做了简要综述。

在激光间接驱动的惯性约束聚变（ICF）中，高强度激光与低密度等离子体发生相互作用，会激发两种受激散射过程：受激布里渊散射和受激拉曼散射。它们会损失激光能量、破坏辐射场对称性、产生超热电子，从而危害聚变点火过程。因此，理解受激散射的物理过程并找到抑制其发展的有效方法，是ICF研究中重点关注的问题。介绍了中国激光聚变研究团队为研究受激散射过程而发展的多个理论模型，以及这些模型在实验数据分析中的具体应用。这些理论模型与实验研究一起，为提升受激散射过程的物理理解发挥了重要作用。

Interfacial magnetic field structures induced by transverse electron-scale shear instability (mushroom instability) are found to be strongly associated with electron and ion dynamics, which in turn will influence the development of the instability itself. We find that high-frequency electron oscillations are excited normal to the shear interface. Also, on a larger time scale, the bulk of the ions are gradually separated under the influence of local magnetic fields, eventually reaching an equilibrium related to the initial shear conditions. We present a theoretical model of this behavior. Such separation on the scale of the electron skin depth will prevent different ions from mixing and will thereafter restrain the growth of higher-order instabilities. We also analyze the role of electron thermal motion in the generation of the magnetic field, and we find an increase in the instability growth rate with increasing plasma temperature. These results have potential for providing a more realistic description of relativistic plasma flows.

在惯性约束聚变物理研究中，等离子体界面处的动理学效应及其时空演化特性近年来受到重点关注，因为它会显著影响激光能量沉积、激光等离子体不稳定性、辐照对称性、黑腔和内爆性能等诸多物理。准确描绘等离子体特征界面附近的动理学效应是惯性约束聚变物理设计的基本需求，也是高能量密度物理中的具有挑战且未完全解决的问题。重点回顾近几年来本团队围绕等离子体动理学效应及其影响开展的一些研究工作：（1）聚变黑腔中金等离子体与靶丸冕区等离子体边缘处的电场结构及其加速的高能离子对内爆对称性的影响；（2）激光光路上高Z-低Z等离子体界面处的电场产生机制及其导致的反常离子扩散对激光等离子体不稳定性的影响；（3）等离子体中电磁场结构的质子照相反演。

当前，激光惯性约束聚变在越来越接近点火的极端能量密度条件下，实验与模拟的偏离逐渐增大，一个关键原因是缺乏对黑腔等离子体状态及其影响黑腔能量学和内爆对称性的细致研究和判断。光学汤姆逊散射主动式、诊断精确、参数完备的优点，使之成为激光惯性约束聚变黑腔等离子体状态参数精密诊断的标准方法。中国面向激光惯性约束聚变研究的光学汤姆逊散射实验技术的发展与神光系列激光装置的建设和在其上开展的物理实验紧密相关。近年来，四倍频汤姆逊散射实验技术在神光III原型和100 kJ激光装置上相继建立，部分实验结果不仅加深了对激光惯性约束聚变靶物理的认识，还反映了实验条件对汤姆逊散射诊断的影响，促进了实验技术的精密化发展。在未来，还需要进一步发展多支路汤姆逊散射、五倍频汤姆逊散射和超热相干汤姆逊散射等新技术，面向点火黑腔条件，大幅提升激光等离子体状态参数的诊断精度，开展新物理机制的探索和研究，在激光惯性约束聚变和其他高能量密度物理科学领域发挥更重要的作用。

为了给快点火集成耦合效率的计算提供关键参数，并为后期高密度压缩奠定高能背光的诊断基础，在神光-Ⅱ升级装置上利用皮秒短脉冲激光驱动产生了X射线背光源，测量了成像分辨率、光通量，获得了短脉冲背光源的辐射特性，进一步成功演示了基于这种短脉冲背光照相技术的间接驱动快点火预压缩密度诊断。实验所得图像与模拟图像结构一致，实测压缩过程中的面密度达到50 mg/cm²。实验还发现了压缩不对称引起的流体不稳定性特征，为后续实验提供了改进方向。