神光Ⅲ主机极向驱动靶丸表面辐照均匀性  

Laser irradiation uniformity for polar direct drive on ShenGuang Ⅲ facility

作　　者：余波[1,2] 丁永坤[1,3] 蒋炜[1,2] 黄天晅[2] 陈伯伦[2] 蒲昱东[2] 晏骥[2] 陈忠靖[2] 张兴[2] 杨家敏[2] 江少恩[2] 郑坚[1] 

机构地区：[1]中国科学技术大学近代物理系,合肥230026 [2]中国工程物理研究院激光聚变研究中心,绵阳621900 [3]北京应用物理与计算数学研究所,北京100088

出　　处：《物理学报》2017年第14期361-370,共10页Acta Physica Sinica

摘　　要：极向驱动是在间接驱动构型的激光装置中,通过重瞄各束激光的位置,实现较均匀的靶丸表面激光辐照,以研究直接驱动惯性约束聚变的关键物理问题.介绍了神光Ⅲ主机装置的激光排布和焦斑特点,以及激光束重瞄方法和靶丸表面激光辐照均匀性优化原则.给出了三阶和五阶超高斯近似下的激光焦斑强度分布,Φ540μm靶丸在能量沉积满足cos^2γ和cosγ假设时靶丸表面最均匀辐照的移束参数,以及二维辐射流体程序模拟最优移束时的内爆对称性结果.二维模拟结果表明,按cos吖假设移束的热斑更对称.分析了激光的束间功率不平衡、激光束重瞄精度和靶丸定位精度对靶丸表面辐照均匀性的影响.模拟结果表明,为了不显著降低靶丸表面辐照均匀性,需要将束间功率不平衡控制在5%以内,激光束重瞄精度和靶丸定位精度控制在7μm以内.Inertial confinement fusion utilizes sufficient laser beams to directly illuminate a spherical capsule,or convert the laser into thermal X-rays inside a high Z hohlraum to drive capsule implosion.The direct drive implosion is one of ways toward central ignition and similar to the indirect drive implosion,but has higher laser energy coupling efficiency and the potential for higher-gain implosion than indirect drive,and needs stringent laser condition.In order to develop and execute the direct drive experiment on the laser facility,which is configured initially for indirect drive,the polar direct drive has been proposed and validated on the Omega laser facility and the National Ignition Facility.The polar direct drive repoints some of the beams toward the polar and equator of the target,thus increasing the drive energy on the polar and equator of capsule and achieving the most uniform irradiation.The present article focuses on the laser irradiation uniformity of the target in polar direct drive on ShenGuangⅢ（SGⅢ） facility.Firstly,the laser beam configuration of the SGⅢ,the characteristics of laser spots,the laser beam repointing strategy and the principle of optimization are introduced.The 48 laser beams are distributed over four cones per hemisphere and the beam centerlines are repointed in polar direct drive.The continuous phase plates（CPPs） of the SGⅢ are designed to have unique shape to make the laser beam with a 250 μm-radius circular section at the laser entrance hole in indirect drive,and thus the laser beams have ellipse cross sections with fixed major axis and different minor axes in different cones.Then,the irradiation uniformity of Φ540 μm target is optimized by the three-dimensional（3D） view factor method on the assumption that the laser intensity distribution is super-Gaussian with three and five orders,and the energy deposition distributions are expressed as cos^2 γ and cos γ.The irradiation nonuniformity of less than 5%on the polar direct drive capsule of 540 μm in diameter

关 键 词：极向驱动 辐照均匀性 激光重瞄 

分 类 号：TN24[电子电信—物理电子学]