针对高压物质密度诊断的激光X射线照相优化设计

激光驱动冲击波能提供高压的物质状态, 是状态方程研究的重要工具. 超短超强激光与固体靶相互作用产生的X射线源, 具有短脉冲、微焦点、高产额、能量可调的特点, 是高压物质密度测量的首选背光源. 本文基于蒙特卡罗程序Geant4建立了X射线照相模型, 客体密度分布由流体力学程序Multi-1D模拟激光冲击加载高压物质获得. 在一维长方体形密度客体情况下, 定义了均方根、峰值偏差与上升沿斜率比三种指标, 对照相图像求解的密度结果进行评价, 开展了照相结果信噪比、分辨率与对比度等参数优化. 并开展了一维圆柱形密度客体的照相模拟, 建立了基于Radon逆变换法的Abel反演算法. 反演结果与模拟设计密度分布符合良好, 要求X射线源半径在5 μm以内; 反演结果与模拟设计密度分布较为一致, 要求X射线源半径在15 μm以内.

Optimization design of laser X-ray radiography for density diagnosis in compressed matter

The shock wave driven by laser is an important tool for investigating equation of state and can provide the state of compressed matter. The X-ray source, generated by the short-pulse intense laser interaction with the solid target, has the properties of short pulse, small spot, high yield and tunable energy. Therefore the X-ray source is the first chosen as a backlighter for the diagnosis of dynamic process. The model of the X-ray radiography is established by Monte Carlo code Geant4. The density distribution in an object is obtained by hydrodynamic code Multi-1D and the laser parameters are obtained by the XGIII laser facility. Under the condition of one-dimensional density the object in the shape of rectangular solid, three evaluation criterions, root mean square, peak value and ratio of rise gradient, are defined for evaluating density results. The signal-to-noise, spatial resolution, and contrast of radiography results have been optimized. First, the signal-to-noise has been optimized and the optimization magnification is 5.6 with the photon yield 10¹². Second, the spatial resolution according to different spot X-ray source has been simulated by designing resolution plate radiography. Third, in the condition of same magnification, the influence of source yield on radiography result has been analyzed. Fourth, the radiography results of different X-ray energy have been simulated. The optimization energy for radiography requests that the penetrability ratio is greater than 1.5 and the photon count in pixel after penetrating the compressed matter is greater than 3000. And the optimum criteria make sure that the radiography images simultaneously have high contrast and high signal-to-noise. The radiography of one-dimensional density object in the shape of cylinder has been simulated. The Abel inversion algorithm is established based on Radon inversion. The inversion result accords well with the designed density distribution in simulation at the request of the radius of X-ray source less than 5 μm. The inversion result basically accords with the designed density distribution in simulation at the request of the radius of X-ray source less than 15 μm. This work will contribute to the measurement experiments on the compressed matter achieved by laser-driven-shock and provide the reference for the optimization of radiography based on X-ray.