基于编码源成像的等离子体密度诊断方法

Method for Electron Density Diagnostics Based on Coded Source Imaging

利用探针光编码源成像可对丝阵负载Z箍缩等离子体内爆实验进行冕区密度诊断,基于阴影像系统,在光路靶区前设计增加一块线阵编码板对入射探针光波前空间分布进行改造.通过模拟成像分析了光路布局中物面选择和偏折角提取;在等离子体的最大密度小于临界密度一个量级时Abel变换式可以采用近轴近似,采用对偏折角样点直接三次样条插值和对Abel变换式的分段积分获得等离子密度分布,其与初始密度设定值相比较为吻合;比较编码板不同疏密度时的反演偏差,对于梯度变化平滑的等离子体,即使条纹比较稀疏也能反演得到很好的结果.结果表明:该方法系统简单,对光源和光学器件性能参数要求较为宽松,调试容易,具有很好的测量适应性,可用于等离子体密度诊断.

A kind of coded-source-imaging-based laser probing diagnostics can be used for the measurements of coronal region electron density in the explosion experiments of wire array Z- pinch.Based on the shadowgraphy system,it just add a linear fringe-pattern mask in front of the target to change the wavefront distribution of incident laser.The selection of object plane and extraction of deflection angle are analyzed by imaging simulation.When the maximum density of plasma is an order of magnitude less than the critical density,paraxial approximation can be used in Abel transform.Cubic spline interpolation of deflection angles and piecewise integral of Abel transform give out the density distribution,which is in good agreement with the setted density value.Compared the inversion errors with different line-pairs coded masks,we can get good results for the plasma with smooth gradient even if the mask fringes are relatively sparse.Calculation shows that this method has a simpler system,and don′t need high performance parameters for light source and optical device,thus it has a good measurement adaptability,and it′s feasible for the diagnosis of plasma density.