钨表面起弧行为及杂质产生机理研究

Unipolar arc is one of the main mechanisms that causes material erosion of tungsten-based first wall and impurities production in the experimental devices of magnetic confinement fusion. Its probability is not only relevant to the surface structure and property of the first wall material, but also relates to transient effects such as ELMs in tokamaks. This application proposes to induce arcing on tungsten using transient effects such as pulsed laser and edge localized modes in the laser coupled radio frequency (RF) plasma device and EAST all superconducting tokamak. The process of the production, continuation and quench for unipolar arc and the erosion trails on the tungsten surface will be analyzed, and the influence of plasma conditions and surface structure and properties of materials on unipolar arc production and motion will be researched, to understand the erosion mechanism of unipolar arc on tungsten surface. The Monte Carlo ERO will be used to simulate the transport behavior of tungsten impurities originated from the erosion by unipolar arc in order to clarify the principal mechanism of tungsten impurities transported into the plasma, and evaluate the contribution of tungsten impurities produced by the unipolar arc to the high Z impurities in the Tokamak. This study can promote the development of high performance and long pulse fusion plasma physics experiment to some extent, and provide experimental basises and accumulate experiences for the operation of EAST and future ITER with full metal wall.

单极弧是磁约束核聚变实验装置中钨基第一壁材料腐蚀和杂质产生的主要原因之一。其发生几率不仅与第一壁材料表面结构和性质有关，还与托卡马克中边界局域模（ELMs）等瞬态效应有关。本申请拟在激光耦合射频等离子体台面装置及EAST全超导托卡马克中，通过脉冲激光和边界局域模等瞬态效应诱导钨表面起弧，分析单极弧产生、持续和熄灭等过程及钨表面腐蚀痕迹，研究等离子体条件和材料表面结构与性质对单极弧的产生和运动规律的影响，理解单极弧对钨材料表面的腐蚀机制；采用蒙特卡罗程序 ERO 模拟单极弧腐蚀产生钨杂质的迁移行为，阐明钨杂质进入等离子体的主要机制，评估单极弧产生的钨杂质对托卡马克装置中高Z杂质的贡献。本项研究可在一定程度上促进高参数长脉冲聚变等离子体物理实验的发展，为EAST和未来ITER全金属壁运行提供实验基础并积累经验。

托卡马克装置中，起弧是等离子体与壁相互作用的关键问题之一，一方面起弧可腐蚀壁材料表面，影响壁材料使用寿命，另一方面，由起弧产生的杂质可进入等离子体，影响等离子体运行。随着高Z金属壁材料的应用和等离子体加热功率的提高，由起弧引起的腐蚀所产生的杂质对等离子体性能的影响越来越大。本项目基于电弧理论，采用COMSOL软件成功模拟了托卡马克壁材料表面电弧熔坑的形成及动态演化过程，在此基础上系统对比分析了不同电弧能流密度和压力参数下电弧坑的形态特征和规律，不同材料（W、Mo、Cu和Al等）之间的差异；利用Python-Opencv自主设计的电弧识别程序，成功筛选出AUG装置中高速视频数据中的电弧痕迹，结合AUG中丰富的等离子体诊断数据（加热功率、ELMs等），详细分析研究了等离子体参数对电弧触发的影响；在EAST装置中发现了两种典型的电弧痕迹，另外，钨表面电弧诱导实验表明纳米丝结构更有利于触发电弧。这些研究对理解托卡马克装置运行中金属壁表面起弧行为提供了重要的数据参考。