二维三温流体力学高性能计算方法研究及程序研制

靶球在辐射驱动下内爆的物理过程是惯性约束聚变（ICF）研究的重要组成部分之一。由于流场的大变形和物理力学过程的复杂性,相关的数值模拟具有相当大的难度。根据研究工作的需求,符尚武等人克服了数值模拟方法上的重重困难,研制成功了二维三温流体动力学程序-LARED-I第一版。该程序是ICF数值模拟中主要的大型程序之一,在应用中取得了多方面的成果。     

惯性约束聚变激光烧蚀驱动内界面不稳定性数值模拟

利用水平集方法和三阶本质无振荡(ENO)方法研究了流体力学界面不稳定性和激光烧蚀驱动内界面不稳定性数值模拟,并用数值算例与LARED-S程序的运算结果进行了比较.数值结果表明此方法计算惯性约束聚变激光烧蚀驱动内界面不稳定性的有效性和精确性.     

视角因子方法在间接驱动ICF中的应用

采用视角因子方法,对间接驱动惯性约束聚变(ICF)过程中从腔内壁辐射到靶丸表面的辐射进行了计算,并分析了激光原型装置上的一个实验的对称性环境。间接驱动ICF系统的不对称性一般来自于激光焦斑和腔体的几何结构,利用视角因子方法,计算X光能量在腔体内的强度分布,将靶丸表面的驱动对称性表示成腔体结构和激光焦斑几何参数的函数。结果表明,采用该方法的程序模拟能够评估腔靶设计的主要参数。     

激光聚变冲击点火物理特性研究

冲击点火是一种新型的惯性约束聚变点火方案,该点火方案具有低点火能量阈值、高增益和较好的流体力学稳定性等优点.本文针对冲击点火的物理特性进行理论分析和数值模拟.首先以一维平板模型对冲击波碰撞的物理过程进行理论研究和分析;然后通过辐射流体力学数值模拟对冲击点火的物理特性进行研究,验证理论分析结果,并考察冲击加载时间对点火的影响. 关键词： 冲击点火 冲击波碰撞 辐射流体力学模拟     

X射线相衬成像技术应用于高能量密度物理条件下内爆靶丸诊断

内爆压缩过程中多层球壳靶丸变化规律的研究是惯性约束聚变的核心内容. 利用相衬成像技术可以提高低Z材料分界面成像衬度的特点在神光Ⅱ大型激光装置上开展了相关研究. 实验通过激光打Ti靶和针孔点背光的方式产生4.75 keV的X射线微点源, 针对内爆压缩过程中的靶丸样品投影成像获得了清晰的多层球壳靶丸图像, 空间分辨率优于10 μm.同时利用一维流体力学数值模拟程序分析了球壳运动的过程, 实验结果与数值模拟结果符合较好.表明了X射线相衬成像技术在高能量密度物理环境下仍然能够提高低Z材料分界面的衬度,获得高质量的物理图像,能够广泛应用于可控聚变能源、 天体物理等前沿科学领域.     

激光聚变内爆流体不稳定性基础问题研究进展

激光聚变有望一劳永逸地解决人类的能源问题,因而受到国际社会的普遍重视,一直是国际研究的前沿热点。目前实现激光惯性约束聚变所面临的最大科学障碍（属于内禀困难）是对内爆过程中高能量密度流体力学不稳定性引起的非线性流动的有效控制,对其研究涵盖高能量密度物理、等离子体物理、流体力学、计算科学、强冲击物理和高压原子物理等多个学科,同时还要具备大规模多物理多尺度多介质流动的数值模拟能力和高功率大型激光装置等研究条件。作为新兴研究课题,高能量密度非线性流动问题充满了各种新奇的现象亟待探索。此外,流体力学不稳定性及其引起的湍流混合,还是天体物理现象（如星系碰撞与合并、恒星演化、原始恒星的形成以及超新星爆炸）中的重要过程,涉及天体物理的一些核心研究内容。本文首先综述了高能量密度非线性流动研究的现状和进展,梳理了其中的挑战和机遇。然后介绍了传统中心点火激光聚变内爆过程发生的主要流体力学不稳定性,在大量分解和综合物理研究基础上,凝练出了目前制约美国国家点火装置（NIF）内爆性能的主要流体不稳定性问题。接下来,总结了国外激光聚变流体不稳定性实验物理的研究概况。最后,展示了内爆物理团队近些年在激光聚变内爆流体不稳定性基础性问题方面的主要研究进展。该团队一直从事激光聚变内爆非线性流动研究与控制,以及聚变靶物理研究与设计,注重理论探索和实验研究相结合,近年来在内爆重要流体力学不稳定性问题的解析理论、数值模拟和激光装置实验设计与数据分析等方面取得了一系列重要成果,有力地推动了该研究方向在国内的发展。     

CH调制靶RT不稳定性增长侧向诊断

流体力学不稳定性是惯性约束聚变中的重要物理问题之一，它直接影响靶丸的压缩效率和点火热斑的有效半径。特别是在激光直接驱动ICF技术路线中，流体力学不稳定性显得更为至关重要。通过分解实验，研究流体力学不稳定性的发展规律进而探索抑制流体力学不稳定性发展的途径，是ICF实验研究中的重要一环。本轮实验利用X射线针孔辅助点投影技术，通过侧向诊断方法，观测了CH平面调制靶在激光直接驱动下的不稳定性演化过程。     

激光驱动的ICF物理研究

惯性约束聚变是近年来发展迅速、具有科学意义和应用前景的研究领域．本文概述了激光驱动的惯性约束聚变的物理过程和值得研究的物理问题；讨论了激光聚变物理与核武器物理的联系，说明军用研究是激光聚变研究近、中期应用的重要方面；介绍了中国工程物理研究院的激光聚变研究工作．     

辐射驱动内爆流线实验测量

内爆速度的测量是惯性约束聚变研究中的核心问题, 是判断聚变点火反应的关键物理量. 在神光II激光装置上, 利用KB显微镜配合时间分辨为10 ps的条纹相机, 对1600 J激光能量注入, 3倍频, 脉宽为1 ns黑腔辐射驱动CH靶球, 获得了清晰的辐射驱动内爆流线轨迹X射线图像. 通过流线轨迹图像给出了最大内爆速度为160 km/s. 利用Multi1D程序对内爆压缩流线和壳层速度变化进行了模拟, 实验数据和理论模拟较符合.     

小孔等离子体运动实验方法

在间接驱动惯性约束聚变的黑腔中,辐射烧蚀的高Z等离子体的流体力学运动过程对激光注入黑腔的效率、辐射场均匀性和通过诊断口的黑腔辐射温度诊断都有显著影响。为研究诊断口在黑腔辐射场中的等离子体缩口过程,用激光产生X光辐射加热低Z泡沫填充的金黑腔诊断口,以激光辐照钛平面靶产生的2～5 keV高能段窄能区X光作为背光源,用X光分幅相机获得了源靶和小孔靶两种靶型的小孔等离子体运动过程图像,研究了X光烧蚀的小孔等离子体的流体力学运动过程,探索了定量测量小孔等离子体面密度的空间分布与时间演化过程的实验诊断方法,初步给出小孔等离子体的面密度。     

LARED集成程序辐射输运模拟的性能优化

分析定位高置信度辐射传输数值模拟效率瓶颈,针对物理模型和数值离散格式的特点,优化求解算法和程序设计,改进激光聚变二维总体LARED集成程序,提高输运建模模拟黑腔靶实验模型的计算效率：在相同的并行计算条件下,辐射输运方程离散求解计算效率提高2倍以上,全过程整体模拟计算时间减半.     

点火内爆靶辐射驱动不对称性全过程数值模拟

为满足分层掺杂点火内爆靶辐射驱动不对称性全过程物理分析的需求,在激光聚变二维总体程序LARED集成上发展了辐射输运建模下的多介质ALE方法-RTALE(Radiative Transfer Arbitrary-Lagrangian-Eulerian)。为提高多介质ALE方法的健壮性,发展了驰豫网格重构算法,该重构算法生成的新网格能自适应流场的变化。数值模拟了激波与气柱相互作用的RM不稳定性实验,模拟的气泡变形程度与试验结果基本一致,其中驰豫网格重构算法中的驰豫因子能够很好地反映流场密度梯度。基于辐射多群输运建模的LARED集成程序能够完整模拟辐射驱动不对称性条件下掺杂点火靶二维内爆过程,克服了传统ALE方法计算不下去和算不好的困难,界面变形程度也符合物理分析。     

A new ignition hohlraum design for indirect-drive inertial confinement fusion

In this paper,a six-cylinder-port hohlraum is proposed to provide high symmetry flux on capsule.It is designed to ignite a capsule with 1.2-mm radius in indirect-drive inertial confinement fusion(ICF).Flux symmetry and laser energy are calculated by using three-dimensional view factor method and laser energy balance in hohlraum.Plasma conditions are analyzed based on the two-dimensional radiation-hydrodynamic simulations.There is no Y_(lm)(l≤4) asymmetry in the six-cylinder-port hohlraum when the influences of laser entrance holes(LEHs) and laser spots cancel each other out with suitable target parameters.A radiation drive with 300 eV and good flux symmetry can be achieved by using a laser energy of 2.3 MJ and peak power of 500 TW.According to the simulations,the electron temperature and the electron density on the wall of laser cone are high and low,respectively,which are similar to those of outer cones in the hohlraums on National Ignition Facility(NTF).And the laser intensity is also as low as those of NIF outer cones.So the backscattering due to laser plasma interaction(LPI) is considered to be negligible.The six-cyliner-port hohlraum could be superior to the traditional cylindrical hohlraum and the octahedral hohlraum in both higher symmetry and lower backscattering without supplementary technology at an acceptable laser energy level.It is undoubted that the hohlraum will add to the diversity of ICF approaches.     

Numerical Investigation Into the Highly Nonlinear Heat Transfer Equation with Bremsstrahlung Emission in the Inertial Confinement Fusion Plasmas

A highly nonlinear parabolic partial differential equation that models the electron heat transfer process in laser inertial fusion has been solved numerically. The strong temperature dependence of the electron thermal conductivity and heat loss term (Bremsstrahlung emission) makes this a highly nonlinear process. In this case, an efficient numerical method is developed for the energy transport mechanism from the region of energy deposition into the ablation surface by a combination of the Crank‐Nicolson scheme and the Newton‐Raphson method. The quantitative behavior of the electron temperature and the comparison between analytic and numerical solutions are also investigated. For more clarification, the accuracy and conservation of energy in the computations are tested. The numerical results can be used to evaluate the nonlinear electron heat conduction, considering the released energy of the laser pulse at the Deuterium‐Tritium (DT) targets and preheating by heat conduction ahead of a compression shock in the inertial confinement fusion (ICF) approach. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

激光惯性约束聚变靶技术现状及其发展趋势北大核心CSCD

靶是激光惯性约束聚变(ICF)研究的物质基础,其质量的好坏对物理实验结果有极其重要的影响。靶本身的特点决定了制靶是一项极其复杂且特色鲜明的系统工程。主要介绍了国内ICF靶制备技术的现状,并对存在的问题及今后一段时期内的发展趋势作了简要说明。     

激光惯性约束聚变中光学汤姆逊散射研究进展

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。     

高阶FD-WENO格式在数值求解Rayleigh-Taylor不稳定性问题中的应用

用高阶加权本质上无振荡有限差分格式(FD-WENO),求解重力作用下高密度比二维流体界面Rayleigh-Taylor不稳定性问题及激光烧蚀Rayleigh-Taylor不稳定性问题,均获得较为理想的数值结果.     

Mathematical modeling of the heating of a fast ignition target by an ion beam

We develop a BIN computer code for simulating the interaction of a monochromatic ion beam with a plasma, which takes into account changes in the spatial distribution of the heated-plasma temperature. This enables us to calculate the heating of both homogeneous and inhomogeneous plasmas with parameters corresponding to their real spatial distributions at the time of maximum compression of the inertial confinement fusion (ICF) target. We present the results of a numerical simulation using the BIN code for the heating of a homogeneous deuterium–tritium plasma by a short pulse of monochromatic ions at various ion velocity and plasma–electron thermal velocity ratios. We also present the results of calculations for the heating of an inhomogeneous plasma of a non-cryogenic target formed as a beryllium deuteride–tritide shell by beams of light, medium, and heavy ions. As the initial distributions, we use the results of numerical simulations for such a target, precompressed by a laser pulse (carried out at the M. V. Keldysh Institute of Applied Mathematics using the DIANA code). We demonstrate the possibility of forming the central ignitor with the parameters sufficient for igniting the targets by beams of ions with energies E ~ 100 ? 400 MeV/u and specific energy densities of the beam Q ～ 5?20 GJ/cm². The required specific energy density drops with increase in the ion energy; however, due to the increased path length, larger-charge ions have to be used.     

The relevance of HED lasers to astrophysics

The role of high energy density (HED) lasers in astrophysics is reviewed, emphasizing connections with laser physics experiments and inertial confinement fusion (ICF). Careful validation of astrophysical methods, by laboratory experiment, by critical comparison of numerical and analytical methods, and by observation are necessary for the development of simulation methods with reliable predictive capability. Recent results from hydrodynamic simulations of stellar evolution, HED laser experiments, and computer simulations will be discussed, and related to stellar evolution and supernovae.     

Theoretical and simulation research of hydrodynamic instabilities in inertial-confinement fusion implosions

Inertial fusion energy(IFE)has been considered a promising,nearly inexhaustible source of sustainable carbon-free power for the world's energy future.It has long been recognized that the control of hydrodynamic instabilities is of critical importance for ignition and high-gain in the inertial-confinement fusion(ICF)hot-spot ignition scheme.In this mini-review,we summarize the progress of theoretical and simulation research of hydrodynamic instabilities in the ICF central hot-spot implosion in our group over the past decade.In order to obtain sufficient understanding of the growth of hydrodynamic instabilities in ICF,we first decompose the problem into different stages according to the implosion physics processes.The decomposed essential physics processes that are associated with ICF implosions,such as Rayleigh-Taylor instability(RTI),Richtmyer-Meshkov instability(RMI),Kelvin-Helmholtz instability(KHI),convergent geometry effects,as well as perturbation feed-through are reviewed.Analytical models in planar,cylindrical,and spherical geometries have been established to study different physical aspects,including density-gradient,interface-coupling,geometry,and convergent effects.The influence of ablation in the presence of preheating on the RTI has been extensively studied by numerical simulations.The KHI considering the ablation effect has been discussed in detail for the first time.A series of single-mode ablative RTI experiments has been performed on the Shenguang-Ⅱlaser facility.The theoretical and simulation research provides us the physical insights of linear and weakly nonlinear growths,and nonlinear evolutions of the hydrodynamic instabilities in ICF implosions,which has directly supported the research of ICF ignition target design.The ICF hot-spot ignition implosion design that uses several controlling features,based on our current understanding of hydrodynamic instabilities,to address shell implosion stability,has been briefly described,several of which are novel.