基于光束参量优化实现直接驱动靶丸均匀辐照  

Uniform irradiation of a direct drive target by optimizing the beam parameters

作　　者：李宏勋[1,2] 张锐[1] 朱娜[1] 田小程[1] 许党朋[1] 周丹丹[1] 宗兆玉 范孟秋 谢亮华 郑天然[1,2] 李钊历 

机构地区：[1]中国工程物理研究院激光聚变研究中心,绵阳621900 [2]中国工程物理研究院研究生部,北京100088

出　　处：《物理学报》2017年第10期198-209,共12页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:61475145)资助的课题~~

摘　　要：在直接驱动惯性约束聚变中,实现靶丸均匀辐照对靶丸压缩特性至关重要,通常要求靶丸表面辐照不均匀度小于1%.现有很多优化高功率激光装置均匀辐照性能的光束排布方案,但受到实际入射光束参量的限制,系统均匀辐照性能难以实现最优化.由于初始辐照不均匀度对靶丸对称压缩特性至关重要,为进一步提高靶丸初始辐照的均匀性,并增加系统对打靶过程中由于靶丸直径变化引起的辐照不均匀的宽容度,从而实现靶丸的中心对称压缩,本文对靶丸表面光束的辐照不均匀度进行了数学分析,并研究了不同入射光束参量下的单光束因子项及其对靶丸均匀辐照的影响.结果表明:对于已知的光束排布结构,存在最优的入射光束参量,使辐照均匀度最高.证明了通过优化入射光束参量提高系统均匀辐照性能的可行性.此外,研究表明单光束因子项与几何因子项存在一定的匹配关系,可通过分析几何因子项的特征,求取与之匹配的单光束因子项,进而获得最优的入射光束参量.本工作为直接驱动靶丸均匀辐照系统的设计和优化提供了一种有效的方法.Laser driven fusion requires a high-degree uniformity in laser energy deposition in order to achieve the high-density compression required for sustaining a thermonuclear burn. Nowadays, uniform irradiation of capsule is still a key issue in direct drive inertial confinement fusion. The direct drive approach is to drive the target with laser light, by irradiating it with a large number of overlapping laser beams. In the direct drive scheme, the laser deposition pattern on the target can be decomposed into a series of Legendre spherical harmonic modes. The high mode （shorter wavelength） nonuniformity can lead to Rayleigh-Taylor instability, which may result in the failure of target compression. This nonuniformity can be suppressed by thermal conduction and beam conditioning technologies, such as continuous phase plate, smoothing by spectral dispersion and polarization smoothing. The low mode （longer wavelength） nonuniformity is related to the number, orientation and power balance of laser beams, which is hard to suppress by thermal conduction and beam conditioning technologies. Generally, the nonuniformity of laser irradiation on a directly driven target should be less than 1% （root mean square, RMS）, to meet the requirement for symmetric compression. Several methods have been proposed to optimize the irradiation configuration in direct drive laser fusion, such as truncated icosahedron with beams at the 20 faces and 12 vertices of an icosaherdron, dodecahedron-based irradiation configurations, self-organizing electrodynamic method, etc. However, limited by the different parameters of incident beams, the irradiation uniformity is often not satisfactory. Therefore, it is necessary to find new way to improve the irradiation uniformity and make it more robust. According to the analytical result, the irradiation nonuniformity can be decomposed into the single beam factor and the geometric factor. Simulation results show that the single beam factor is mainly determined by the parameters of the incident beams,

关 键 词：惯性约束聚变 直接驱动 均匀辐照 入射光束参量 

分 类 号：TL632[核科学技术—核技术及应用]