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Title: Type-I ELM mitigation by continuous lithium granule gravitational injection into the upper tungsten divertor in EAST
Contributors: Sun, Zhen
Yuzhong, Qian
Maingi, Rajesh
Wang, Yifeng
Wang, Yumin
Nagy, Alex
Tritz, Kevin
Lunsford, Robert
Gilson, Erik
Zuo, Guizhong
Xu, Wei
Huang, Ming
Meng, Xiancai
Mansfield, Dennis K.
Zang, Qing
Zhu, Xiang
Lin, Xin
Liu, Haiqing
Duan, Yanmin
Zhang, Ling
Lyu, Bo
Liu, Yong
Wang, Liang
Bortolon, Ale
Xu, Guosheng
Gong, Xianzu
Hu, Jiansheng
Keywords: Lithium
Impurity seeding
Edge localized modes
Issue Date: Apr-2021
Publisher: Nuclear Fusion
Abstract: Large edge-localized modes (ELMs) were mitigated by gravitational injection of lithium granules into the upper X-point region of the EAST device with tungsten plasma-facing components. The maximum ELM size was reduced by ~ 70% in high βN H-mode plasmas. Large ELM stabilization was sustained for up to about 40 energy confinement times, with constant core radiated power and no evidence of high-Z or low-Z impurity accumulation. The lithium granules injection reduced the edge plasma pedestal density and temperature and their gradients, due to increased edge radiation and reduced recycling from the plasma-facing components. Ideal stability calculations using the ELITE code indicate that the stabilization of large ELMs correlates with improved stability of intermediate-n peeling-ballooning modes, due to reduced edge current resulting from the profile changes. The pedestal pressure reduction was partially offset by a core density increase, which resulted in a modest ~ 7% drop in core stored energy and normalized energy confinement time. We surmise that the remnant small ELMs are triggered by the penetration of multiple Li granules just past the separatrix, similar to small ELMs triggered by deuterium pellet [S. Futatani et al., Nucl. Fusion 54 (2014) 073008]. This study extends previous ELM elimination with Li powder injection [R. Maingi et al., Nucl. Fusion 58 (2018) 024003] in EAST because 1) use of small, dust-like powder and the related potential health hazards were eliminated, and 2) use of macroscopic granules should be more applicable to future devices, due to deeper penetration than dust particles, e.g. inside the separatrix with velocities ~ 10 m/s in EAST.
Appears in Collections:PPPL Collaborations

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