Effect of ELM pacing on morphology evolution and erosion of tungsten as a plasma-facing material in a fusion environment
Effect of ELM pacing on morphology evolution and erosion of tungsten as a plasma-facing material in a fusion environment
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DOI：
10.1016/j.jnucmat.2018.05.035
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发表时间：
2018-09
影响因子：
3.1
通讯作者：
G. Sinclair;S. Gonderman;J. Tripathi;A. Hassanein
中科院分区：
文献类型：
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作者：
G. Sinclair;S. Gonderman;J. Tripathi;A. Hassanein
减缓未来聚变装置中的瞬态等离子体事件是必要的，以尽量减少对周围等离子体面向组件（pfc）的热损伤。由边缘局部化模式（ELM）引起的强热负荷会导致PFC表面的熔化和飞溅。ELM缓解涉及以更高的频率触发这些事件，这降低了传递给材料的有效热通量。不幸的是，同时，高通量的He+离子照射在钨(W)上，这是未来pfc的主要候选材料，已被证明可以驱动树状纳米结构的发展，称为fuzz。热导率和机械强度的大幅下降与绒毛的形成需要重新考虑ELM减缓对材料损伤和侵蚀的影响。在CMUXE的UHFI-II设施中进行了三种不同类型的实验，旨在表征He+离子辐照与脉冲热负荷之间的协同效应（用脉冲毫秒激光复制）。无论频率如何，暴露于脉冲热载荷下的W样品都会以页岩状表面形貌的形式进行粗化。同时加入脉冲热载荷的He+离子辐照促进了熔融材料的飞溅，并引起了显著的孔隙形成。将频率增加到10 Hz会产生更光滑的W表面。而在总平均激光功率一定的情况下，增加频率会降低激光能量密度，从而显著减少表面熔化，增强早期模糊的形成。所获得的结果提出了一个重要的问题，即是否可以调整ELM缓解参数来退火任何氦诱导的表面结构而不引起不可持续的熔融材料飞溅。
Mitigation of transient plasma events in a future fusion device is necessary to minimize thermal damage on surrounding plasma facing components (PFCs). Intense heat loading caused by an edge-localized mode (ELM) can lead to melting and splashing of the PFC surface. ELM mitigation involves triggering these events at higher frequencies, which lowers the effective heat flux imparted on the material. Unfortunately, concurrent, high-flux He+ion irradiation on tungsten (W), which is the leading candidate material for future PFCs, has been shown to drive the development of an arborescent nanostructure, known as fuzz. Large drops in thermal conductivity and mechanical strength with fuzz formation necessitate a reconsideration of the impact of ELM mitigation on material damage and erosion. Three different types of experiments designed to characterize the synergistic effect between He+ion irradiation and pulsed heat loading (replicated with a pulsed millisecond laser) were conducted in the UHFI-II facility at CMUXE.W samples exposed to pulsed heat loading underwent roughening in the form of a shale-like surface morphology, regardless of frequency. The addition of simultaneous He+ion irradiation with pulsed heat loading promoted splashing of molten material and caused significant pore formation. Increasing the frequency to 10 Hz produced a smoother W surface. However, when the total average laser power was held constant, increasing the frequency decreased the laser energy density, which significantly decreased surface melting and enhanced early stage fuzz formation. Results obtained raise an important question of whether ELM mitigation parameters can be tuned to anneal out any He-induced surface structuring without causing unsustainable splashing of molten material.