The influence of plasma-surface interaction on the performance of tungsten at the ITER divertor vertical targets
The influence of plasma-surface interaction on the performance of tungsten at the ITER divertor vertical targets
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DOI：
10.1088/1361-6587/aaaf62
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发表时间：
2018-04-01
影响因子：
2.2
通讯作者：
Pitts, R. A.
中科院分区：
文献类型：
--
作者：
De Temmerman, G.;Hirai, T.;Pitts, R. A.
在ITER导流器的高热通量区，钨(W)材料将暴露在高热通量的低能粒子（例如H、D、T、He、Ne和/或N）中。结合长脉冲操作，这意味着影响远远超过今天托卡马克实验中达到的最高值。单个单块顶部表面的成形和用于前缘保护的垂直目标的倾斜导致表面热流通量增加，从而提高了表面温度，减小了保持在再结晶和晶粒生长开始温度以下的裕度。已知W在暴露于低能粒子（无论是H还是He）的高影响后会发生显著的形态变化。对这些形态变化的地层条件进行了分析，并与不同作业阶段垂直目标的预期条件进行了比较。结论是，在ITER中，H和he相关效应都可能发生。特别地，he诱导的纳米结构（也被称为“模糊”）的情况进行了回顾。在外部垂直靶的有限区域可能出现模糊层，内部靶通常是净Be沉积区。考虑边缘局域模式（elm）的影响和热导率降低的模糊生长速率的简单分析表明，在elm诱导的热漂移过程中，退火的发生可能限制了模糊的厚度。等离子体暴露不仅可以改变材料的形貌，还可以改变材料的力学和热性能。对现有文献进行了回顾，但现有数据不足以定量地得出这些影响对ITER的重要性和程度。由于ITER的高表面温度，W再结晶是一个需要考虑的重要影响，因为它会导致材料强度的降低。本文提出了一种方法来制定W材料的运行预算，即在很大一部分材料再结晶之前，在给定温度下转流材料可以运行的时间。总的来说，虽然在ITER运行过程中明显会发生明显的表面损伤，但就等离子体运行而言，其可容忍的损伤程度目前尚不清楚。
The tungsten (W) material in the high heat flux regions of the ITER divertor will be exposed to high fluxes of low-energy particles (e.g. H, D, T, He, Ne and/or N). Combined with long-pulse operations, this implies fluences well in excess of the highest values reached in today's tokamak experiments. Shaping of the individual monoblock top surface and tilting of the vertical targets for leading-edge protection lead to an increased surface heat flux, and thus increased surface temperature and a reduced margin to remain below the temperature at which recrystallization and grain growth begin. Significant morphology changes are known to occur on W after exposure to high fluences of low-energy particles, be it H or He. An analysis of the formation conditions of these morphology changes is made in relation to the conditions expected at the vertical targets during different phases of operations. It is concluded that both H and He-related effects can occur in ITER. In particular, the case of He-induced nanostructure ( also known as 'fuzz') is reviewed. Fuzz formation appears possible over a limited region of the outer vertical target, the inner target being generally a net Be deposition area. A simple analysis of the fuzz growth rate including the effect of edge-localized modes (ELMs) and the reduced thermal conductivity of fuzz shows that the fuzz thickness is likely to be limited by the occurrence of annealing during ELM-induced thermal excursions. Not only the morphology, but the material mechanical and thermal properties can be modified by plasma exposure. A review of the existing literature is made, but the existing data are insufficient to conclude quantitatively on the importance and extent of these effects for ITER. As a consequence of the high surface temperatures in ITER, W recrystallization is an important effect to consider, since it leads to a decrease in material strength. An approach is proposed here to develop an operational budget for the W material, i.e. the time the divertor material can be operated at a given temperature before a significant fraction of the material is recrystallized. In general, while it is clear that significant surface damage can occur during ITER operations, the tolerable level of damage in terms of plasma operations currently remains unknown.