Exfoliation of the tungsten fiberform nano-structure by unipolar arcing in the LHD divertor plasma
Exfoliation of the tungsten fiberform nano-structure by unipolar arcing in the LHD divertor plasma
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LHD 偏滤器等离子体中单极电弧对钨纤维纳米结构的剥离
DOI：
10.1088/0029-5515/51/10/102001
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发表时间：
2011
期刊：
影响因子：
--
通讯作者：
LHD Experiment Group
中科院分区：
文献类型：
--
作者：
M.Tokitani;S.Kajita;S.Masuzaki;Y.Hirahata;N.Ohno;T.Tanabe;LHD Experiment Group
将在线性偏滤器模拟器（NAGDIS）中产生的钨纳米结构（W-绒毛）暴露于大螺旋装置（LHD）偏滤器等离子体仅2秒（1次发射），以研究由于高磁场条件下的高热/颗粒负载而引起的剥落/侵蚀和微观修改。在大约一半的W-绒毛区域（6× 10 mm 2）上清楚地观察到非常精细和随机移动的单极电弧痕迹。模糊的表面剥落的连续移动的弧点，即使在很短的曝光时间。这是在具有高磁场的大型等离子体约束装置中首次观察到单极电弧和W-绒毛结构本身的某些区域的剥落。每个电弧轨迹的典型宽度和深度分别约为8微米和1微米，并且电弧点在微米尺度上随机移动。采用计盒法对弧形轨迹的分形进行了分析，估计弧形轨迹的分维（D）为D≈ 1.922。这一数值表明，弧斑的运动是布朗运动，几乎不受磁场的影响。应该注意的是，这种大规模的剥离由于单极电弧可能会增加钨装甲的表面侵蚀，并作为一个严重的杂质源聚变等离子体。
The tungsten nanostructure (W-fuzz) created in the linear divertor simulator (NAGDIS) was exposed to the Large Helical Device (LHD) divertor plasma for only 2 s (1 shot) to study exfoliation/erosion and microscopic modifications due to the high heat/particle loading under high magnetic field conditions. Very fine and randomly moved unipolar arc trails were clearly observed on about half of the W-fuzz area (6× 10 mm 2). The fuzzy surface was exfoliated by continuously moving arc spots even for the very short exposure time. This is the first observation of unipolar arcing and exfoliation of some areas of the W-fuzz structure itself in a large plasma confinement device with a high magnetic field. The typical width and depth of each arc trail were about 8 µm and 1 µm, respectively, and the arc spots moved randomly on the micrometre scale. The fractality of the arc trails was analysed using a box-counting method, and the fractal dimension (D) of the arc trails was estimated to be D≈ 1.922. This value indicated that the arc spots moved in Brownian motion, and were scarcely influenced by the magnetic field. One should note that such a large scale exfoliation due to unipolar arcing may enhance the surface erosion of the tungsten armour and act as a serious impurity source for fusion plasmas.