Achieving record hot spot energies with large HDC implosions on NIF in HYBRID-E
Achieving record hot spot energies with large HDC implosions on NIF in HYBRID-E
复制标题
在 HYBRID-E 的 NIF 上通过大型 HDC 内爆实现创纪录的热点能量
作者：
A. Kritcher;A. Zylstra;D. Callahan;O. Hurricane;C. Weber;J. Ralph;D. Casey;A. Pak;K. Baker;B. Bachmann;S. Bhandarkar;J. Biener;R. Bionta;T. Braun;M. Bruhn;C. Choate;D. Clark;J. Di Nicola;L. Divol;T. Doeppner;V. Geppert;S. Haan;J. Heebner;V. Hernandez;D. Hinkel;M. Hohenberger;H. Huang;C. Kong;S. Le Pape;D. Mariscal;E. Marley;L. Masse;K. Meaney;M. Millot;A. Moore;K. Newman;A. Nikroo;P. Patel;L. Pelz;N. Rice;H. Robey;J. Ross;M. Rubery;J. Salmonson;D. Schlossberg;S. Sepke;K. Sequoia;M. Stadermann;D. Strozzi;R. Tommasini;P. Volegov;C. Wild;S. Yang;C. Young;M. Edwards;O. Landen;R. Town;M. Herrmann
HYBRID-E是一种惯性约束聚变内爆设计，通过增加圆柱形黑腔中的胶囊尺度来增加耦合到热点的能量，同时在国家点火装置的当前实验极限内运行。与以前的混合设计相比，混合E在固定的密封舱尺寸下减小了黑腔规模，从而提高了黑腔效率和耦合到密封舱的能量，并使用交叉束能量转移（CBET）通过在不同波长（Δ λ > 0）下操作内（23°和30°）和外（44°和50°）激光束来控制内爆对称性。小的壳体与囊体比设计可能会受到黑腔腰部驱动不足的影响。结果表明，在低气体填充的黑腔（0.3mg/cm ~ 3 He）中，只要内外光束之间有很小的波长间隔（Δ λ 1-2 A），就可以控制黑腔的对称性，并且在黑腔的腰部有足够的驱动力来对称地驱动外径为1180 μm的胶囊。该活动是首次使用CBET控制0.3 mg/cm 3氦填充黑腔的对称性，这是迄今为止最低的气体填充密度，Δ λ > 0。我们发现热点P2的灵敏度（单位：μm/埃）（波长间隔40-50 μm/A）比在高气体填充的黑腔和以前使用0.6 mg/cm 3的黑腔气体填充密度的更长脉冲设计中观察到的灵敏度更高。目前没有迹象表明随着Δ λ的增加转移滚降，这表明在圆柱形黑腔中使用CBET可以驱动甚至更长的脉冲或更大的胶囊。我们表明，辐射通量的对称性得到很好的控制过程中的脚的脉冲，整个内爆可以调谐对称的CBET在这个系统中的存在下，低水平的激光背散射出的黑腔和低水平的热电子生产从强烈的激光等离子体相互作用。辐射流体动力学模拟可以准确地反映早期激波的对称性，并可作为设计工具，但不能预测脉冲峰值期间的后期辐射通量对称性，因此采用半经验模型设计实验。1100 μm内半径内爆的氘氚（DT）分层试验表明，当增加DT燃料层厚度以减轻烧蚀体中的缺陷导致的烧蚀体进入热点的流体动力学混合时，性能接近于在高达360 km/s的速度下模拟的预期，并在该速度下记录了产额。然而，当内爆速度增加时，由于这些缺陷引起的混合影响性能。这些实验的测量产率与模拟产率之比与观察到的混合水平直接相关。这些模拟表明，减少混合，通过改善胶囊缺陷，可以导致更高的性能。此外，未来的实验计划减少这个尺度的滑行时间，峰值压缩和激光结束之间的延迟，以增加热点会聚和压力。与1100 μm内径的内爆相比，为了减少几百ps的滑行时间，HYBRID-E还部署了1050 μm内径的胶囊，这导致了更高的热点压力和170 kJ的聚变能量产额。
HYBRID-E is an inertial confinement fusion implosion design that increases energy coupled to the hot spot by increasing the capsule scale in cylindrical hohlraums while operating within the current experimental limits of the National Ignition Facility. HYBRID-E reduces the hohlraum scale at a fixed capsule size compared to previous HYBRID designs, thereby increasing the hohlraum efficiency and energy coupled to the capsule, and uses the cross-beam energy transfer (CBET) to control the implosion symmetry by operating the inner (23° and 30°) and outer (44° and 50°) laser beams at different wavelengths ( Δ λ > 0). Small case to capsule ratio designs can suffer from insufficient drive at the waist of the hohlraum. We show that only a small amount of wavelength separation between the inner and outer beams ( Δ λ 1–2 A) is required to control the symmetry in low-gas-filled hohlraums (0.3 mg/cm3 He) with enough drive at the waist of the hohlraum to symmetrically drive capsules 1180 μm in outer radius. This campaign is the first to use the CBET to control the symmetry in 0.3 mg/cm3 He-filled hohlraums, the lowest gas fill density yet fielded with Δ λ > 0. We find a stronger sensitivity of hot spot P2 in μm per Angstrom (40–50 μm/A wavelength separation) than observed in high-gas-filled hohlraums and previous longer pulse designs that used a hohlraum gas fill density of 0.6 mg/cm3. There is currently no indication of transfer roll-off with increasing Δ λ, indicating that even longer pulses or larger capsules could be driven using the CBET in cylindrical hohlraums. We show that the radiation flux symmetry is well controlled during the foot of the pulse, and that the entire implosion can be tuned symmetrically in the presence of the CBET in this system, with low levels of laser backscatter out of the hohlraum and low levels of hot electron production from intense laser–plasma interactions. Radiation hydrodynamic simulations can accurately represent the early shock symmetry and be used as a design tool, but cannot predict the late-time radiation flux symmetry during the peak of the pulse, and semi-empirical models are used to design the experiments. Deuterium–tritium (DT)-layered tests of 1100 μm inner radius implosions showed performance close to expectations from simulations at velocities up to ∼360 km/s, and record yields at this velocity, when increasing the DT fuel layer thickness to mitigate hydrodynamic mixing of the ablator into the hot spot as a result of defects in the ablator. However, when the implosion velocity was increased, mixing due to these defects impacted performance. The ratio of measured to simulated yield for these experiments was directly correlated with the level of observed mixing. These simulations suggest that reducing the mixing, e.g., by improving the capsule defects, could result in higher performance. In addition, future experiments are planned to reduce the coast time at this scale, delay between the peak compression and the end of the laser, to increase the hot spot convergence and pressure. To reduce the coast time by several hundred ps compared to the 1100 μm inner radius implosions, HYBRID-E has also fielded 1050 μm inner radius capsules, which resulted in higher hot spot pressure and a fusion energy yield of ∼170 kJ.