JOREK 模拟中 ITER H 模式双 SPI 下的等离子体团漂移与第一壁热沉积
Plasmoid drift and first wall heat deposition during ITER H-mode dual-SPIs in JOREK simulations
AI总结：
本文利用 JOREK 模拟 ITER H 模式双 SPI 破裂缓解，揭示低氖比例下等离子体团漂移降低缓解效率，并量化第一壁热沉积能量冲击，表明良好同步可显著降低壁面损伤风险。
摘要：
在热猝灭（TQ）期间通过破碎弹丸注入（SPI）实现热流缓解，是 ITER 破裂缓解策略的主要要素之一。其效率在很大程度上取决于 SPI 与目标等离子体，并最终通过沉积到面向等离子体部件（PFC）上的热量来检验。为研究这一问题，本文使用 JOREK 对 ITER 基线 H 模式以及一种“降级 H 模式”进行了掺氖双 SPI 模拟，分别考虑注入器同步良好与不同步的情况，重点关注第一壁热流及其能量冲击。研究发现，在基线 H 模式等离子体中，低氖比例 SPI 在碎片到达台基区时表现出强烈的大半径方向等离子体团漂移，并伴随边缘随机化。由此导致显著的密度排出和向外热流，从而降低了缓解效率。这种漂移运动可以通过注入更高氖比例的弹丸，或考虑破裂前约束退化来加以缓解，从而提高辐射份额。研究发现，在注入早期阶段，辐射热流在碎片注入位置附近达到峰值，随后由于平行杂质输运而逐渐松弛。良好的同步性可以显著缓解整体辐射不对称性。本文对局部热流进行了时间积分，以提供其能量冲击，用于壁面热损伤评估。对于全弹丸注入的基线 H 模式情形，诊断口的不锈钢可能在注入口附近发生熔化，这是可接受的，且第一壁钨瓦片不会发生任何熔化。对于采用四分之一弹丸 SPI 的降级 H 模式情形（其总体积为全弹丸的 1/4），在 SPI 不同步时最大能量冲击接近不锈钢的可承受极限，而在完全同步时则远低于该极限。
英文摘要：
The heat flux mitigation during the Thermal Quench (TQ) by the Shattered Pellet Injection (SPI) is one of the major elements of disruption mitigation strategy for ITER. It's efficiency greatly depends on the SPI and the target plasma, and is ultimately checked by the heat deposition on to the PFCs. To investigate this, JOREK simulations of neon-mixed dual-SPIs into ITER baseline H-mode and a "degraded H-mode" with and without good injector synchronization are performed with focus on the first wall heat flux and its energy impact. It is found that low neon fraction SPIs into the baseline H-mode plasmas exhibit strong major radial plasmoid drift as the fragments arrive at the pedestal, accompanied by edge stochasticity. Significant density expulsion and outgoing heat flux occurs as a result, reducing the mitigation efficiency. Such drift motion could be mitigated by injecting higher neon fraction pellets', or by considering the pre-disruption confinement degradation, thus improving the radiation fraction. The radiation heat flux is found to peak in the vicinity of the fragment injection location in the early injection phase, while it relaxes later on due to parallel impurity transport. The overall radiation asymmetry could be significantly mitigated by good synchronization. Time integration of the local heat flux is carried out to provide its energy impact for wall heat damage assessment. For the baseline H-mode case with full pellet injection, melting of the stainless steel of the diagnostic port could occur near the injection port, which is acceptable, without any melting of the first wall tungsten tiles. For the degraded H-mode cases with quarter-pellet SPIs, which have 1/4 total volume of a full pellet, the maximum energy impact approaches the tolerable limit of the stainless steel with un-synchronized SPIs, and stays well below such limit for the perfectly synchronized ones.
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