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中国物理学会期刊
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  • 在大型激光装置通过激光直接驱动薄壳靶内爆发展的中子或带电粒子实验平台,具有高产额、短脉冲、各向同性、准单能等优点,常用于核物理、核天体物理、高能量密度物理等研究.本文提出了一种数据驱动的高产额直接驱动薄壳靶设计方法,结合激光功率、波长差、移束策略等优化,十万焦耳激光装置玻璃靶实验的中子产额达到1.00×1014,聚变转换效率达到4.5‰,大幅提升了十万焦耳激光装置的中子产额和聚变转换效率.验证实验结果同时表明,提高激光功率能够显著提高内爆速度、离子温度和中子产额;多色激光能够抑制束间能量转移造成的激光散射,提高能量耦合效率,改善内爆对称性,并提升离子温度和中子产额;不同移束策略对中子产额、离子温度、中子发射区对称性等内爆性能无显著影响.

    High-yield, short-pulse, quasi-monoenergetic neutron and charged particle experimental platforms, developed through laser direct drive implosion of thin-shell targets, are widely used in research areas such as nuclear physics, nuclear astrophysics, and high energy density physics. To achieve high neutron yield in laser direct drive implosion experiments, a data-driven high yield direct drive implosion design method is proposed. When physical understanding and numerical simulations are imprecise, this approach utilizes existing experimental data to establish empirical models and optimize parameters such as pulse shapes, capsule diameter, capsule thickness, fill pressures, laser spot diameter, etc. It effectively resolves the inherent trade-offs among implosion velocity, hot-spot symmetry, and shell-fuel mixing while balancing the relationship between one-dimensional yield and three-dimensional effects. The design process is initiated by utilizing preliminary experimental data and extensive numerical calculations to calibrate the Multi1D code. This includes refining its physical models of thermal conduction and shell-fuel mixing, as well as adjusting coefficients such as the flux limiter and diffusion multiplier. Furthermore, scaling relations of laser absorption efficiency, yield over clean (YOC), and ion temperature are derived. Subsequently, the calibrated Multi1D code, integrated with these empirical scaling relations, is employed to perform quantitative simulations to determine the optimal shell thickness and fuel pressure of the glass targets, and to predict experimental yield, ion temperature, and convergence ratio. Validation experiments using 1200 μm diameter glass targets were conducted on the 100 kJ laser facility. The results demonstrated that by applying the data-driven high yield direct drive implosion design and optimizing laser power and wavelength, a neutron yield of 1.00×1014 was achieved, representing a substantial enhancement over previous results on 100 kJ laser facility. The fusion conversion efficiency, defined as the fusion output divided by the laser energy incident on the capsule, was 4.5‰, slightly higher than the reported of NIF glass targets. It was also found that increasing laser power significantly improved implosion velocity, ion temperature and neutron yield. Additionally, the use of wavelength separation among the different cone beams effectively suppressed laser losses caused by crossed-beam energy transfer, resulting in strongly improved energy coupling efficiency, hot-spot symmetry, and neutron yield. The four-color laser configuration performed significantly better than the three-color laser. In contrast, various laser repointing strategies showed no significant impact on implosion performance, including neutron yield, ion temperature, and hot-spot symmetry.

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