东方超环(EAST)装置中等离子体边界锂杂质的碰撞-辐射模型

在东方超环(EAST)装置中,由于大量锂化壁处理的使用,切向可见光摄像机拍摄到等离子体边界通常存在一条由锂(Li)杂质形成的绿色发光带.本文基于EAST边界等离子体参数条件,基于碰撞-辐射模型给出由已知边界等离子体状态推算Li绿光光强的空间分布的具体方法,并针对简化后的一维径向分布问题,收集、处理OPEN-ADAS数据库的数据,采用软件Mathematica 10.4.1编写相应的数值计算程序,分别输入EAST工作于低约束(L)与高约束(H)模时获得的两组边界电子温度、密度分布数据,给出并分析比较了利用该模型的计算结果.此项工作对于未来建立通过测量及反演边界锂杂质特征谱线强度的空间分布来重构边界等离子体状态的全新技术和研究存在三维磁场扰动条件下的边界等离子体行为均具有重要的理论参考价值.

A collisional-radiative model for lithium impurity in plasma boundary region of Experimental Advanced Superconducting Tokamak

A green emission layer caused by lithium impurity is universally observed in plasma boundary region of Experimental Advanced Superconducting Tokamak (EAST) via a visible-light camera, where lithium coating is normally adopted as a routine technique of wall conditioning. In this article, in order to estimate the spatial distribution of green light intensity of this emission layer according to the given real parameter distributions of edge plasmas, a practicable method is proposed based on a collisional-radiative model. In this model, a finite number of energy levels of lithium are taken into account, and proper simplifications of convection-diffusion equations are made according to the order-of-magnitude analysis. We process the atomic data collected from the OPEN-ADAS database, and develop a corresponding program in Mathematica 10.4.1 to solve the simplified one-dimensional problem numerically. Estimation results are obtained respectively for the two sets of edge plasma profiles of EAST in L-mode and H-mode regimes, and both clearly show a good unimodal structure of the spatial distribution of green light intensity of this emission layer. These analyses actually provide the spatial distributions of lithium impurities at different energy levels, not only indicating the spatial distribution of the intensity of this emission layer induced by lithium impurity but also revealing the physical processes that lithium experiences in edge plasma. There are some different and common characteristics in the spatial distribution of the intensity of this emission layer in these two important cases. This emission layer is kept outside the last closed magnetic surface in both cases while it becomes thinner with a higher intensity peak in H-mode case. Besides, the sensitivity of this algorithm to the measurement error of edge plasma profile is also explored in this work. It is found that the relative errors of the numerical results obtained by our proposed method are comparable to those of edge plasma profiles. This work provides important theoretical references for developing a new practical technique of fast reconstructing edge plasma configurations in EAST based on the emission of lithium impurity, and may further contribute a lot to the studies of edge plasma behaviors when three-dimensional perturbation fields are adopted.