Author Affiliations
Abstract
1 Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
2 Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
3 Graduate School, China Academy of Engineering Physics, Beijing, China
4 HEDPS, Center for Applied Physics and Technology, and College of Engineering, Peking University, Beijing 100871, China
A recently proposed octahedral spherical hohlraum with six laser entrance holes (LEHs) is an attractive concept for an upgraded laser facility aiming at a predictable and reproducible fusion gain with a simple target design. However, with the laser energies available at present, LEH size can be a critical issue. Owing to the uncertainties in simulation results, the LEH size should be determined on the basis of experimental evidence. However, determination of LEH size of an ignition target at a small-scale laser facility poses difficulties. In this paper, we propose to use the prepulse of an ignition pulse to determine the LEH size for ignition-scale hohlraums via LEH closure behavior, and we present convincing evidence from multiple diagnostics at the SGIII facility with ignition-scale hohlraum, laser prepulse, and laser beam size. The LEH closure observed in our experiment is in agreement with data from the National Ignition Facility. The total LEH area of the octahedral hohlraum is found to be very close to that of a cylindrical hohlraum, thus successfully demonstrating the feasibility of the octahedral hohlraum in terms of laser energy, which is crucially important for sizing an ignition-scale octahedrally configured laser system. This work provides a novel way to determine the LEH size of an ignition target at a small-scale laser facility, and it can be applied to other hohlraum configurations for the indirect drive approach.
Matter and Radiation at Extremes
2022, 7(6): 065901
Author Affiliations
Abstract
1 HEDPS, Center for Applied Physics and Technology, and School of Physics, Peking University, Beijing 100871, China
2 Department of Applied Physics, School of Physics and Electronics, Hunan University, Changsha 410082, China
3 HEDPS, Center for Applied Physics and Technology, and College of Engineering, Peking University, Beijing 100871, China
4 Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
5 Graduate School, China Academy of Engineering Physics, Beijing 100193, China
6 China Academy of Engineering Physics, Mianyang 621900, China
Through nonequilibrium molecular dynamics simulations, we provide an atomic-scale picture of the dynamics of particles near the surface of a medium under ultra-strong shocks. This shows that the measured surface velocity vf under ultra-strong shocks is actually the velocity of the critical surface at which the incident probe light is reflected, and vf has a single-peaked structure. The doubling rule commonly used in the case of relatively weak shocks to determine particle velocity behind the shock front is generally not valid under ultra-strong shocks. After a short period of acceleration, vf exhibits a long slowly decaying tail, which is not sensitive to the atomic mass of the medium. A scaling law for vf is also proposed, and this may be used to improve the measurement of particle velocity u in future experiments.
Matter and Radiation at Extremes
2021, 6(2): 026903
强激光与粒子束
2020, 32(4): 042001
1 北京应用物理与计算数学研究所, 北京 100088
2 中国工程物理研究院 研究生院, 北京 100088
3 北京大学 应用物理与技术研究中心, 北京 100871
系统地梳理了激光间接驱动点火靶内爆压缩的物理过程, 使用理论方法和一维流体力学模拟给出了靶丸内爆过程中的关键定标律公式。通过这些定标律公式获得了在给定黑腔辐射温度、飞行熵增因子、整形速度和烧蚀材料的条件下, 靶丸装量--半径参数空间的点火岛区域。研究了靶丸性能参数随辐射温度、飞行熵增因子等的变化规律: 当靶丸所处黑腔辐射温度升高时, 内爆的稳定性将变好; 设计上在靶丸装量不变的条件下, 靶丸半径需要减小。当靶丸的飞行熵增因子增大时, 内爆增益略微减小, 内爆稳定性变好; 但是点火阈值因子减小导致点火岛的区域变窄。当靶丸的整形速度增大时, 点火岛的区域略微变大, 内爆稳定性变化不显著; 设计上在靶丸装量不变的条件下, 需要增大靶丸半径, 这会导致靶丸壳层形状因子变大。当改变靶丸烧蚀材料, 提高质量烧蚀速率与烧蚀压时, 能量增益变大且稳定性增强; 设计上在靶丸装量不变的条件下, 需要减小靶丸半径。
激光聚变 间接驱动 内爆动力学 靶丸设计 定标律 laser fusion indirect-driven implosion dynamics capsule design scaling law 强激光与粒子束
2019, 31(6): 062001
Author Affiliations
Abstract
Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
The basic energy balance model is applied to analyze the hohlraum energetics data from the Shenguang (SG) series laser facilities and the National Ignition Facility (NIF) experiments published in the past few years. The analysis shows that the overall hohlraum energetics data are in agreement with the energy balance model within 20% deviation. The 20% deviation might be caused by the diversity in hohlraum parameters, such as material, laser pulse, gas filling density, etc. In addition, the NIF's ignition target designs and our ignition target designs given by simulations are also in accordance with the energy balance model. This work confirms the value of the energy balance model for ignition target design and experimental data assessment, and demonstrates that the NIF energy is enough to achieve ignition if a 1D spherical radiation drive could be created, meanwhile both the laser plasma instabilities and hydrodynamic instabilities could be suppressed.
Energy balance model Energy balance model Hohlraum energetics Hohlraum energetics National Ignition Facility (NIF) National Ignition Facility (NIF) Shenguang (SG) series Shenguang (SG) series Matter and Radiation at Extremes
2017, 2(1): 22
Author Affiliations
Abstract
1 Institute of Applied Physics and Computational Mathematics, Beijing 100094, China
2 Graduate School, China Academy of Engineering Physics, Beijing 100088, China
3 Center for Applied Physics and Technology, Peking University, Beijing 100871, China
4 Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
5 China Academy of Engineering Physics, Mianyang 621900, China
X-ray drive asymmetry is one of the main seeds of low-mode implosion asymmetry that blocks further improvement of the nuclear performance of “high-foot” experiments on the National Ignition Facility [Miller et al., Nucl. Fusion 44, S228 (2004)]. More particularly, the P2 asymmetry of Au's M-band flux can also severely influence the implosion performance of ignition capsules [Li et al., Phys. Plasmas 23, 072705 (2016)]. Here we study the smoothing effect of mid- and/or high-Z dopants in ablator on Au's M-band flux asymmetries, by modeling and comparing the implosion processes of a Ge-doped ignition capsule and a Si-doped one driven by X-ray sources with P2 M-band flux asymmetry. As the results, (1) mid- or high-Z dopants absorb hard X-rays (M-band flux) and re-emit isotropically, which helps to smooth the asymmetric Mband flux arriving at the ablation front, therefore reducing the P2 asymmetries of the imploding shell and hot spot; (2) the smoothing effect of Ge-dopant is more remarkable than Si-dopant because its opacity in Au's M-band is higher than the latter's; and (3) placing the doped layer at a larger radius in ablator is more efficient. Applying this effect may not be a main measure to reduce the low-mode implosion asymmetry, but might be of significance in some critical situations such as inertial confinement fusion (ICF) experiments very near the performance cliffs of asymmetric X-ray drives.
Inertial confinement fusion Inertial confinement fusion Implosion Implosion Low-mode distortion Low-mode distortion M-band flux asymmetry M-band flux asymmetry High-Z dopant High-Z dopant Matter and Radiation at Extremes
2017, 2(2): 69
Author Affiliations
Abstract
1 Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
2 Research Center of Laser Fusion, Chinese Academy of Engineering Physics, Mianyang 621900, China
3 Center for Applied Physics and Technology, Peking University, Beijing 100871, China
4 Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
5 China Academy of Engineering Physics, Mianyang 621900, China
The octahedral spherical hohlraums have natural superiority in maintaining high radiation symmetry during the entire capsule implosion process in indirect drive inertial confinement fusion. While, in contrast to the cylindrical hohlraums, the narrow space between the laser beams and the spherical hohlraum wall is usually commented. In this Letter, we address this crucial issue and report our experimental work conducted on the SGIII-prototype laser facility which unambiguously demonstrates that a simple design of cylindrical laser entrance hole (LEH) can dramatically improve the laser propagation inside the spherical hohlraums. In addition, the laser beam deflection in the hohlraum is observed for the first time in the experiments. Our 2-dimensional simulation results also verify qualitatively the advantages of the spherical hohlraums with cylindrical LEHs. Our results imply the prospect of adopting the cylindrical LEHs in future spherical ignition hohlraum design.
Spherical hohlraum Laser propagation Cylindrical laser entrance hole Laser spot movement Matter and Radiation at Extremes
2016, 1(1): 2
Author Affiliations
Abstract
1 Institute of Applied Physics and Computational Mathematics, Beijing 100088, China
2 Research Center of Laser Fusion, Chinese Academy of Engineering Physics, Mianyang 621900, China
3 Center for Applied Physics and Technology, Peking University, Beijing 100871, China
4 Collaborative Innovation Center of IFSA, Shanghai Jiao Tong University, Shanghai 200240, China
5 China Academy of Engineering Physics, Mianyang 621900, China
Corrigendum Text: On page 2 of this letter, there is a misprint in the unit. The unit of the geometrical dimension of the spherical hohlraums on this page should always be “mm” rather than “mm”, i.e. in the second paragraph, “…with 800 J per beam at 0.35 mm…” should be “…with 800 J per beam at 0.35 μm…”, “The slit of 400 mm width is parallel…” should be “The slit of 400 μm width is parallel…”, “The laser focal diameter is about 500 mm…” should be “The laser focal diameter is about 500 μm…”; in the third paragraph, “…we take 850 μm as the radius…” should be “…we take 850 mm as the radius…”, “The LEH radius RL is 400 mm…” should be “The LEH radius RL is 400 μm…”, “…the radius of the cylindrical LEH outer ring is taken as 1.5 RL = 600 mm” should be “…the radius of the cylindrical LEH outer ring is taken as 1.5 RL = 600 μm”. This mistake does not affect any of the main results of the original letter.
Matter and Radiation at Extremes
2016, 1(2): 133
北京应用物理与计算数学研究所, 北京 100094
不同辐射建模对于腔内辐射场描述的精确程度不同,需要分析不同建模对腔内辐射温度的影响。开展了三温建模与辐射多群输运建模下LARED集成程序数值模拟两孔球型黑腔模型,实现了球腔的完整数值模拟。数值模拟结果表明,三温与辐射多群输运模拟的等离子体状态接近,辐射温度存在差异。物理分析显示辐射温度差异的主要原因是使用的辐射不透明度,修改辐射不透明度参数后的三温计算结果与输运计算符合更好,从而可以用三温建模更快更准确地估计出所需的激光能量和功率。
惯性约束聚变 辐射多群输运 二维LARED集成程序 辐射热传导 辐射不透明度 inertial confinement fusion multi-group radiation transfer 2D LARED-Integration code radiation thermal conduction opacity 强激光与粒子束
2016, 28(4): 042001
1 中国工程物理研究院 激光聚变研究中心, 绵阳 621900
2 北京应用物理与计算数学研究所, 北京 100088
在神光Ⅱ升级装置上完成了国际上首次间接驱动快点火集成实验。实验采用双台阶脉冲整形激光注入黑腔产生X射线准等熵压缩锥壳靶,实现了高密度压缩,然后采用皮秒超短脉冲激光注入加热燃料。实验中观测到中子产额由皮秒激光注入前的5×103增加到2.2×105,中子产额增益达到44倍,实验证实了皮秒激光具有明显燃料加热效果。该实验为进一步开展快点火热斑形成效率和相关物理研究奠定了基础。
激光聚变 快点火 集成实验 中子产额 laser fusion fast ignition integrated experiment neutron yield 强激光与粒子束
2015, 27(11): 110101
