针对神光II升级装置的直接驱动快点火集成实验靶的初步设计

Preliminary target design for integrated direct-drive fast ignition experiments on Shenguang-II upgrade facility

神光II激光装置升级完成后,激光能量将大幅提高,同时配备皮秒拍瓦激光束,能够满足快点火研究在万焦耳级平台开展集成实验的需求.神光II升级装置设计原则是以间接驱动为主,兼顾直接驱动.尽管直接驱动只是替代方案,然而由于直接驱动在快点火预压缩中具备一定优势,如能量利用率较高、对快点火导引锥预热较少、便于诊断等,因此需要探索基于神光II升级装置的直接驱动快点火靶设计.本文针对神光II升级装置的激光条件,利用辐射流体程序Multi1D对集成实验用快点火直接驱动靶的尺寸进行了初步内爆压缩设计和优化.在激光条件固定的情况下,优化无充气单层靶球的半径、厚度,尽可能实现高的密度、面密度.得到最优靶参数为外半径420μm,壳层厚度35μm,与靶球定标关系验证一致.根据超热电子定标关系,计算表明压缩过程实现的最高面密度与皮秒拍瓦激光产生的超热电子射程基本匹配.

The laser energy will be increased substantially when the Shenguang-II laser facility upgrade is completed and the petawatt picosecond laser beam will be equipped at the same time. For the fast ignition approach, direct-drive implosions have some advantages over indirect-drive ones, such as higher energy efficiency and lower mixing of cone material into fuel. Based on Shenguang-II upgraded laser facility, integrated direct-drive fast ignition experiments will be carried out and it will contribute to the further understanding of the relevant physics such as integrated coupling efficiency. The radiation hydrodynamic code Multi1D is used to design fast-ignition targets, and the optimized target parameters are achieved. The optimized target has a relatively thick wall （35 μm） and 420 μm-outer-radius CH shell, which are consistent with the scaling laws in target design. The deposition in the optimization target of the hot electrons generated by the picosecond petawatt pulse is also calculated according to the hot electrons scaling relation. The results show that the achieved areal density is high enough to stop the hot electrons.