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在双锥对撞点火激光核聚变方案中, 两个锥口相距约100 μm放置的金锥内氘氚球冠靶在高功率纳秒激光烧蚀驱动下, 获得沿金锥的球对称压缩和加速, 形成沿着金锥轴向的超音速高密度喷流, 出射喷流在两个金锥的几何中心发生对撞减速并形成聚变密度等离子体. 在对撞过程中, 高速运动喷流的动能转化为内能, 实现对等离子体的预加热, 与此同时, 皮秒拍瓦激光产生的高能快电子从垂直方向入射并加热高密度等离子体, 使其快速升温达到聚变温度, 实现聚变点火. 2020年在中国科学院上海光学精密机械研究所高功率激光联合实验室神光II升级激光装置上, 我们利用总能量为10 kJ的八路纳秒激光进行了两轮实验. 实验利用包括X射线汤姆逊散射、硬X射线单色背光成像、X射线条纹和分幅成像等多种主动、被动诊断方法对超音速高密度喷流对撞过程进行了高时空分辨研究, 实验测量发现, 在单锥口形成的超音速等离子体喷流密度为5.5—8 g/cm3; 在对撞过程中形成了阻滞时间约200 ps的高密度等离子体, 中心密度达到了(46 ± 24) g/cm3. 通过对等离子的温度、速度的分析发现, 对撞过程中动能到内能的转换效率高达89.5%.A collision of supersonic jets in the double-cone ignition scheme is realized experimentally. With a very high deceleration, the supersonic jets merge into a high density plasma core, which will be further fast heated to ignition condition. Both the density and temperature of the plasma core are increased due to nearly 100% of kinetic energy of the jets converted into the internal energy. Some diagnostic tools are used to characterize the plasma, including X-ray Thomson scattering, hard X-ray monochromatic backlighting, X-ray streak imaging and framing imaging. The density of the supersonic jet arrive at about 5.5–8 g/cm3. During colliding, a stagnation phase lasts about 200 ps, and the maximum density of the plasma core is increased to (46 ± 24) g/cm3. By analyzing the velocity and temperature before and after colliding, it is found that 90% of the kinetic energy is converted into thermal energy.
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Keywords:
- inertial confinement fusion /
- fast ignition /
- double-cone ignition
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图 1 实验设计 (a)等熵压缩激光波形设计, 以及该波形下的压缩流线; (b)实验设置, 主要的X射线诊断分布
Fig. 1. Design of the experiment: (a) The profile of laser pulse, together with the implosion of the fuel shell; (b) configuration of the experiment setup, X-ray images for the compressed plasma are installed on the horizontal plane.
图 2 X射线条纹成像 (a)双锥靶照片, 沿轴线的等离子体成像在条纹相机的光阴极; (b)单锥口喷出等离子体; (c)双锥对撞等离子体
Fig. 2. X-ray streak image: (a) The target configuration of double cones, the plasma along the cone axis is imaged; (b) the plasma jet from a single cone, ejecting time and the vertical velocity were measured; (c) the colliding plasma from double cones. All images are illustrated in same color scale.
图 3 X射线汤姆逊散射光谱 (a)温度拟合; (b)电子密度拟合
Fig. 3. X-ray Thomson scattering spectrum: (a) Temperature fitting; (b) the average density fitting.
图 4 对撞等离子体二维时间演化 (a)不同时刻双锥顶中心对撞等离子体自发光图像; (b)自发光区域横向、纵向和光强随时间演化信息
Fig. 4. Two-dimensional temporal evolution of the colliding plasma: (a) Self emission from the colliding plasma in the center of the double cone tips; (b) evolution of size and brightness of the colliding plasma core.
图 5 X射线单色背光成像 (a)压缩前时刻双锥阴影图; (b)双锥对撞最大压缩时刻阴影图; (c)单锥喷出等离子体阴影; (d)对撞等离子体密度、面密度随时间演化; (e)对撞等离子体横向密度、面密度分布; (f)单锥口等离子体横向密度、面密度分布
Fig. 5. X-ray monochromatic backlighting radiography: (a) The radiography image of double cone before compression time. Row data of an undriven double cone target, the shape of the cone is clearly seen, and the bright spots on the top and bottom are the self-emission from the laser ablated shells. (b) The radiography image of a colliding plasma at the maximum compression time. (c) The radiography image from a single cone. (d) The time revolution of the colliding plasma density ρ and areal density ρD before and after the maximum compression. (e) Line profile of the ρ and ρD at the center of the cones for panel (b). (f) Line profile of the ρ and ρD at the center of the cones for panel (c).
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[1] Lindl J D 1994 AIP Conference Proceedings 318 635
[2] Tabak M, Hammer J, Glinsky M E, Kruer W L, Wilks S C, Woodworth J, Campbell E M, Perry M D, Mason R J 1994 Phys. Plasmas 1 1626
Google Scholar
[3] Kodama R, Norreys P A, Mima K, Dangor A E, Evans R G 2001 Nature 412 798
Google Scholar
[4] Murakami M, Nagatomo H 2005 Nucl. Instrum. Methods Nucl. Instrum. Methods Phys. Res. Sect. A 544 67
Google Scholar
[5] Azechi H, Sakaiya T, Watari T, et al. 2009 Phys. Rev. Lett. 102 235002
Google Scholar
[6] Betti R, Zhou C D, Anderson K S, Perkins L J, Theobald W, Solodov A A 2007 Phys. Rev. Lett. 98 155001
Google Scholar
[7] Theobald W, Bose A, Yan R, et al. 2017 Phys. Plasmas 24 120702
Google Scholar
[8] Zylstra A B, Kritcher A L, Hurricane O A, Callahan D A, Baker K, Braun T, Casey D T, Clark D 2021 Phys. Rev. Lett. 126 025001
Google Scholar
[9] Town R 2020 Laser Indirect Drive Input to NNSA 2020 Report (NNSA)
[10] Craxton R S, Anderson K S, Boehly T R, et al. 2015 Phys. Plasmas 22 110501
Google Scholar
[11] Montgomery D S 2016 Phys. Plasmas 23 055601
Google Scholar
[12] Smalyuk V A, Robey H F, Alday C L, et al. 2018 Phys. Plasmas 25 072705
Google Scholar
[13] Zhang J, Wang W, Yang X H, Wu D, Ma Y Y, Jiao J L, Zhang Z, Wu F Y, Yuan X H, Li Y T, Zhu J Q 2020 Phil. Trans. R. Soc. A 378 20200015
Google Scholar
[14] Wang W, Gibbon P, Sheng Z M, Li Y T 2015 Phys. Rev. Lett. 114 015001
Google Scholar
[15] Sakata S, Lee S, Morita H, et al. 2018 Nat. Commun. 9 3937
Google Scholar
[16] Wu F, Yang X H, Ma Y Y, Zhang Q, Zhang Z, Yuan X H, Liu H, Liu Z, Zhong J Y, Zheng J, Li Y T, Zhang J 2022 High Power Laser Sci. Eng. 10 e12
Google Scholar
[17] Fletcher L B, Kritcher A L, Pak A E, et al. 2014 Phys. Rev. Lett. 112 145004
Google Scholar
[18] Glenzer S H, Redmer R 2009 Rev. Mod. Phys. 81 1625
Google Scholar
[19] Theobald W, Solodov A A, Anderson K S, et al. 2014 Nat. Commun. 5 5785
Google Scholar
[20] Arkadiev V A, Bjeoumikhov A A, Haschke M, Langhoff N, Legall H, Stiel H, Wedell R 2007 Spectrochimica Acta Part B 62 577
Google Scholar
[21] Del Ría M S , Dejus R J 2011 Proc. SPIE 8141 814115
Google Scholar
[22] Yi S, Si H, Fang K, Fang Z H, Wu J, Qi R, Zhang Z, Wang Z 2022 J. Opt. Soc. Am. B 39 A61
Google Scholar
[23] Lawson J D 1957 Proc. Phys. Soc. Sect. B 70 6
Google Scholar
[24] Atzeni S, Meyer-ter-Vehn J 2009 The Physics of Inertial Fusion: Beam Plasma Interaction, Hydrodynamics, Hot Dense Matter (International Series of Monographs on Physics) (Oxford: Oxford University Press) p39
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