激光冲击波压缩稠密铝辐射不透明度实验研究

Experimental studies on the opacity of dense aluminum compressed by a laser-driven shock waves

基于稠密物质辐射不透明度的理论计算目前有相当大的难度,而稠密物质高精度不透明度数据又对聚变研究中的理论设计和模拟以及状态诊断等方面非常有用.在"神光II"激光装置上建立一发次中能同时测量背光谱、样品自发谱和吸收谱的大谱窗高分辨椭圆弯晶测谱系统,并利用一维辐射流体力学程序MULTI仿真冲击波碰撞压缩样品的过程.在测量中,用点投影背光法、激光烧蚀冲击波碰撞压缩产生稠密铝(Al)样品,激光镱等离子体3d—4f跃迁辐射为短脉冲背光提供样品吸收谱时空分辨诊断,在一发次打靶中得到了背光谱、样品自发谱和X射线吸收精细结构谱,以及稠密Al辐射吸收谱向长波偏移.实验结果给出了诊断能谱区稠密Al相对透射率分布和吸收谱偏移量.这些工作都有益于丰富不透明度这一基础研究领域和进一步开拓许多重要应用.

The high-precise opacity of the dense plasma has important applications in the design and simulation of fusion research, and in plasma diagnostics. Base on the novel technique of point-projection backlighting, a broadband high-resolution elliptical crystal X-ray spectrometer, which is used to measure simultaneously the self-emission spectrum, the backlighting source spectrum, and the trans- mission spectrum in one shot, is designed on the Shengguang-II laser facility. The process of the colliding-shock-compressed sample by laser-driven shock waves is also investigated using a one-dimensional radiation hydrodynamics code MULTI. In the measurement, the dense plasma, produced in aluminum by colliding shocks driven by laser beams, reaches a peak density several times that of a solid, and the short backlighting from the 3d--4f transition bands of ytterbium is used as an absorption source for time- and space-resolving diagnostics. Several experimental results are obtained, they are the X-ray source spectrum, the transmission spectrum, and the self- emission spectrum of the dense A1 sample in one shot obtained by using the point-projection method, as well as X-ray-absorption fine-structure spectra, and the changes in the K-shell photo-absorption edge of aluminum as it was compressed by a laser-driven shock waves. The transmissivity distribution and red- shift around 80 n~ （with respect to the cold value of 1.56 keV） of the dense aluminum are also obtained. The data obtained are further analysed. As a result, a new theoretical model is developed.