镁和铝样品特征等离子体的L壳层X射线吸收特性研究

【作者】 刘红杰；

【导师】 张保汉；

【作者基本信息】 中国工程物理研究院北京研究生部 ， 核能科学与工程， 2002， 硕士

【摘要】 激光等离子体所特有的极端物理环境使我们很难用直接的手段获取等离子体状态参数，长期以来，光谱诊断在激光等离子体诊断领域发挥着重要作用。等离子体的发射谱利吸收谱是光谱诊断在实际应用中的两个方面。X射线在介质中被吸收过程主要有三种形式：光电离、光激发、逆轫致吸收，这三种微观过程尤其是光电离和光激发与原子结构密切相关。本工作采用不可分辨跃迁系(UTA)模型对光谱结构进行处理，并发展了计算样品等离子体辐射不透明度的方法。求解Saha方程时考虑了离化势下降修正，并用量子亏损理论(QDT)处理高主量子数组态，从而大大减少了计算量。 在“星光-Ⅱ”激光装置上，选择金为背光源材料、镁和铝为样品材料，分别采用点投影背光法和多层靶面背光法探测样品等离子体的L壳层吸收的特性。实验中观察到镁样品等离子体属于类铍离子的2p~2-2p3d跃迁系、类锂离子的lS~22S-ls~23p跃迁系利类铍离子的2s~2-2s3p跃迁系，以及铝样品等离子体分别属于类锂离子的2s-3p和2p-3d跃迁系、类铍离子的2s~2-2s3p、2s2p-2s3d、2p~2-2p3d跃迁系以及类硼离子的2s~22p-2s~23d跃迁系。 实验中推得镁样品特征等离子体的电子温度在50～60eV之间，物质密度为0．01±0．002g／cm~3，在局域热动平衡情况下我们的理论计算结果与实验符合较好。由理论计算结果与实验的比较，我们还推得铝样品等离子体的电子温度在34eV附近，样品等离子体的离化度分布的理论计算结果与实验观测也相符合。 这些理论利实验数据对于辐射不透明度研究、惯性约束聚变以及X射线激光均有一定的参考价值。更多还原

【Abstract】 For the typical physics states of the laser plasma, it is difficult to obtain the plasma parameters directly. Spectroscopic diagnostics play an important role in the field of plasma diagnostics. The emission and absorption spectra can be used. The main absorption mechanisms include photoexcitation (bound-bound transition), photoionization (bound-free transition), and inverse bremsstrahlung (free-free transition), which relate to the atomic structre. Based on unresolved transition array model(UTA), we developed a method to calculate the transmission spectra of the sample plasma. The depression of ionization potential (DIP) is considered in solving the Saha-equations, and the quantum effect theory is used to treat the atomic states with high principal quantum numbers..The L-shell X-ray absorption measurement of Mg and Al sample plasma has been performed on "Xing-Guang II" high power laser facility, in which point projection spectroscopy (pps) techniques and multi-layered target were employed. The gold is chosen as the backlighter for its unique pseudocontinuous spectrum from the O-band emission. The absorption lines of Li-like Is22s-ls23p transition arrays and Be-like 2p2-2p3d 2s2-2s3p transition arrays are clearly observed in experiment I, and the absorption lines of Li-like 2s-3p 2p-3d transition arrays Be-like 2s2-2s3p 2s2p-2s3d 2p2-2p3d transition arrays and the B-like 2s22p-2s23d transition arrays in experiment II.The electron temperature of Mg sample characteristic plasma is determined 50~60eV, and the mass density 0.01?.002g/cm3. In local thermodynamic equilibrium(LTE), the predicted transmission spectrum is calculated and the calculation results are in agreement with the experiment. With the comparison between the calculations and experimental results in experiment II, we infer that the electron temperature of the Al sample plasma is about 34eV.更多还原