混合驱动中直驱激光焦斑尺寸对点火性能的影响

doi:10.19596/j.cnki.1001-246x.8619

摘要/Abstract

摘要：

研究针对混驱点火模型, 保持直驱激光能量不变, 针对1 200, 1 400和1 500 μm直驱光焦斑尺寸, 采用数值模拟, 研究其对点火性能的影响。研究表明: 直驱光焦斑尺寸是影响混驱点火性能的敏感因素。1 500 μm焦斑尺寸可实现近一维点火。1 400 μm焦斑尺寸放能接近一维放能的40%。1 200 μm焦斑尺寸点火失败, 仅仅处于燃烧等离子体状态。分析表明, 1 200 μm焦斑尺寸条件下点火失败的原因是: 其产生的局部强光强和高驱动不对称性, 会导致燃料熵增加及燃料面密度扰动增加。燃料熵的增加将会降低燃料压缩性, 不利于创造高温高压点火条件, 形成的燃烧波较弱。燃料面密度扰动增加会导致燃烧后壳层不稳定性剧烈增长。推断在小焦斑尺寸条件下, 弱燃烧波及高燃料面密度扰动增长, 会导致高密度尖钉难以被有效点燃, 无法形成升温与燃烧的正反馈。同时, 燃料区域内界面不稳定性发展产生的尖钉结构将降低热斑温度, 产生的气泡结构将引起热斑体积迅速变大, 导致热斑快速降温乃至点火失败。

关键词: 混合驱动, 焦斑尺寸, 焦斑重叠, 驱动不对称性, 惯性约束聚变

Abstract:

The direct drive laser is the key factor in hybrid drive inertial confinement fusion. Its drive asymmetry has a great influence on the ignition performance of nuclear fusion. Using the same laser power, the impacts of the direct drive laser focal spot size on the ignition performance of a hybrid drive model are studied. It is shown that the size of the laser focal spot is a key parameter to influence the ignition performance of the hybrid drive model. When the size of the laser focal spot is 1 500 μm, the neutron yield of the target is close to the one got by the one dimensional implosion. When the 1 400 μm laser focal spot is used, the neutron yield is 40% of the one got by the one dimensional implosion. However, it is failed to ignite for the 1 200 μm laser focal spot. The high drive asymmetry caused by the small laser focal spot can increase the adiabat in the fuel. The fuel compressibility will decrease when the adiabat is increased, which goes against creating the ignition condition. In this way, the ignition wave is weak. Meanwhile, the high drive asymmetry can lead a high perturbation of the fuel areal density. The perturbation growth of the fuel areal density can make the shell asymmetry grow greatly when the ignition wave is formed. Under the conditions of the weak ignition wave and the high fuel areal density perturbation, the fuel spike with a high density is hard to be ignited. Therefore, the positive feedback between the increase of hotspot temperature and the ignition is restrained. Meanwhile, the fuel spike can decrease the hotspot temperature. The fuel bubble can lead the hotspot expand rapidly. All these factors will make the ignition performance decrease when a small laser focal spot is used.

Key words: hybrid drive, size of laser focal spot, laser overlap, drive asymmetry, inertial confinement fusion

李志远, 李纪伟, 王立锋, 戴振生, 谷建法, 何民卿, 吴俊峰, 叶文华, 贺贤土. 混合驱动中直驱激光焦斑尺寸对点火性能的影响[J]. 计算物理, 2023, 40(2): 189-198.

Zhiyuan LI, Jiwei LI, Lifeng WANG, Zhensheng DAI, Jianfa GU, Minqing HE, junfeng WU, Wenhua YE, Xiantu HE. Impacts of Direct Drive Laser Focal Spot Size on Ignition Performance of Hybrid Drive Inertial Confinement Fusion[J]. Chinese Journal of Computational Physics, 2023, 40(2): 189-198.

图/表 15

图1 一维靶模型(a) 靶丸材料；(b) 辐射源和激光源

Fig.1 One-dimensional target design (a) capsule material; (b) radiation source and laser source

表1 一维内爆参数

Table 1 One dimensional implosion parameters

t_imp/ns	V_imp/(km · s^-1)	Adiabat	Bangtime/ns	Stagnation time/ns	at the stagnation time			Neutron yield	Yield/MJ
t_imp/ns	V_imp/(km · s^-1)	Adiabat	Bangtime/ns	Stagnation time/ns	P_hs/Gbar	Ti_hs/keV	ρR_fuel/(g · cm^-2)	Neutron yield	Yield/MJ
7.72	445	3.7	7.98	7.95	1 069	8.7	1.04	7.08 × 10¹⁸	20

图2 光强沿角向分布

Fig.2 The distribution of the laser intensity

表2 二维平均内爆参数

Table 2 Two-dimensional implosion parameters

焦斑尺寸/μm	t_imp/ns	V_imp/(km·s^-1)	Adiabat	Bangtime/ns	Stagnation time/ns	at the stagnation time			Neutron yield	Yield/MJ
焦斑尺寸/μm	t_imp/ns	V_imp/(km·s^-1)	Adiabat	Bangtime/ns	Stagnation time/ns	P_hs/Gbar	Ti_hs/keV	ρR_fuel/(g·cm^-2)	Neutron yield	Yield/MJ
1 200	7.68	423	5.37	7.98	7.97	312	4.57	0.9	6.80 × 10¹⁶	0.192
1 400	7.7	430	4.05	8.03	7.97	516	5.94	0.96	2.89 × 10¹⁸	8.14
1 500	7.75	439	3.74	8.02	7.99	934	7.34	1.14	7.00 × 10¹⁸	19.90
1D	7.72	445	3.7	7.98	7.95	1 069	8.7	1.04	7.08 × 10¹⁸	20.00

图3 (a) 临界面光强和(b)混合驱动压的时变RMSE

Fig.3 Evolution of RMSE about (a) laser intensity on critical surface and (b) hybrid drive pressure

图4 (a) 燃料面密度和(b)热斑界面时变RMSE

Fig.4 Evolution of RMSE about (a) fuel areal density and (b) hotspot interface

图5 主要内爆参量对ITF贡献

Fig.5 The contributions of the key implosion parameters on ITF

图6 三个焦斑尺寸条件下主燃料层熵随时间的变化曲线

Fig.6 Evolution of the adiabat in the fuel layer under the conditions of the three cases

图7 1 200 μm焦斑尺寸条件下间驱冲击波进入DT气体区时冲击波位置图

Fig.7 The shock waves' contour when the indirect drive shock comes into the DT gas region under the condition of 1 200 μm focal spot radius

图8 三个焦斑尺寸条件下离子温度和热斑质量随热斑面密度变化曲线

Fig.8 The relationship between the ion temperature and the hotspot areal density and the relationship between the hotspot mass and the hotspot areal density under the different focal spot radius

图9 1 200 μm焦斑尺寸条件下燃料层和热斑密度温度分布

Fig.9 The ion temperature contour and the density contour of the fuel and hotspot under the condition of 1 200 μm focal spot radius

图10 (a) 1 400 μm和(b) 1 500 μm焦斑尺寸壳层和热斑密度温度分布

Fig.10 The ion temperature contour and the density contour of the fuel and hotspot (a) 1 400 μm; (b) 1 500 μm

表3 优化设计靶内爆参数

Table 3 Implosion parameters of the optimized design

t_imp/ns	V_imp/(km · s^-1)	Adiabat	Bangtime/ns	Stagnation time/ns	at the stagnation time			Neutron yield	Yield/MJ
t_imp/ns	V_imp/(km · s^-1)	Adiabat	Bangtime/ns	Stagnation time/ns	P_hs/Gbar	Ti_hs/keV	ρR_fuel/(g · cm^-2)	Neutron yield	Yield/MJ
7.88	420	3.35	8.17	8.12	609	5.9	1.18	4.9 × 10¹⁸	13.8

图11 优化设计后1 400 μm焦斑尺寸燃料面密度和热斑界面时变RMSE

Fig.11 Evolution of RMSE about the fuel areal density and the hotspot interface for the optimized design

图12 优化设计后1 400 μm焦斑尺寸壳层和热斑密度温度分布

Fig.12 The ion temperature contour and the density contour of the fuel and hotspot for the optimized design

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