Plasmoid drift and first wall heat deposition during ITER H-mode dual-SPIs in JOREK simulations

D. Hu, F.J. Artola, E. Nardon, M. Lehnen, M. Kong, D. Bonfiglio, M. Hoelzl, G.T.A. Huijsmans, the JOREK Team2024年8月Nuclear FusionIF 3 出版社

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 parameters, and is ultimately characterised by the heat deposition on to the plasma facing components. To investigate such heat deposition, 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 armour 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 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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ENThis paper is of interest to fusion researchers studying disruption mitigation techniques, especially those working on SPI-based approaches for ITER. It provides valuable insights into the complex plasma dynamics and heat deposition patterns during SPI events.#ITERdisruptionmitigation #SPIheatdeposition #JOREKsimulations

This paper investigates the heat flux mitigation during the thermal quench (TQ) by the shattered pellet injection (SPI) in ITER. The study uses JOREK simulations to analyze the heat deposition on the first wall and its energy impact. It found that low neon fraction SPIs can cause strong plasmoid drift and edge stochasticity, reducing mitigation efficiency. Higher neon fraction or pre-disruption confinement degradation can improve radiation fraction. Good SPI synchronization can also mitigate radiation asymmetry.

この論文は、ITER の崩壊緩和戦略の重要な要素である破砕ペレット注入 (SPI) の熱負荷緩和効果を調べています。JOREK シミュレーションにより、ネオン混合デュアル SPI が ITER の基準 H モードおよび劣化 H モードプラズマに与える影響を分析しました。ペレット注入時の主半径方向のプラズモイドドリフトや、エッジの乱流化による密度排出と熱流出が、緩和効率を低下させることがわかりました。ネオン濃度の増加や、事前の閉じ込め劣化を考慮することで、この問題は改善できると示唆されています。