Pedestal and ELM response to impurity seeding in JET advanced scenario plasmas
Pedestal and ELM response to impurity seeding in JET advanced scenario plasmas
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DOI：
10.1088/0029-5515/48/9/095004
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发表时间：
2008-08
期刊：
影响因子：
3.3
通讯作者：
M. Beurskens;G. Arnoux;A. S. Brezinsek;C. Challis;P. D. de Vries;C. Giroud;A. Huber;S. Jachmich-S.-Jachmi
中科院分区：
文献类型：
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作者：
M. Beurskens;G. Arnoux;A. S. Brezinsek;C. Challis;P. D. de Vries;C. Giroud;A. Huber;S. Jachmich-S.-Jachmi
先进场景等离子体通常必须在低密度和高功率下运行，导致等离子体-表面相互作用区域出现热边缘温度和随之而来的功率处理问题。 JET 的实验正在通过探索使用外来杂质晶种和 D2 膨化来减少热通量来解决这个问题。本文提出的实验延续了 JET 中高三角度的先进托卡马克 (AT) 场景研究路线，重点关注边缘基座的表征以及使用氘和/或轻杂质燃料（氖、氮）的 ELM 行为。在典型的 JET AT 条件下，外来杂质的注入和 D2 膨化都对边缘基座产生显着影响。 ELM 能量损失 ΔWELM/Wdia 可降至 3% 以下，最大 ELM 穿透深度可限制在 r/a > 0.7，从而增强了在大等离子体半径下可持续内部传输势垒的可能性。这些条件可以在两个独立的域中实现，辐射功率分数 (Frad) 为 30% 或分数 >50%。在较低的 Frad 处，ELM 为 I 型，并且保持高基座压力，但偶尔仍可能出现较大的 ELM。当 Frad > 50% 时，基座压力下降 30-50%，但 ELM 降级为 III 型。 Frad ~ 40% 的中间状态对于 ITB 场景没有吸引力，因为大型 I 型 ELM 在主要的 III 型 ELM 阶段（化合物类型 I/III）期间间歇性发生。单独使用 D2 燃料即可获得 Frad = 30%，而需要氖气或氮晶种才能实现 Frad > 50%。仅对氮播种进行了有限数量的测试，初步结论是，一旦辐射分数匹配，等离子体边缘行为与氖播种的情况类似。
Advanced scenario plasmas must often be run at low densities and high power, leading to hot edge temperatures and consequent power handling issues at plasma–surface interaction zones. Experiments at JET are addressing this issue by exploring the use of extrinsic impurity seeding and D2 puffing to reduce heat fluxes. The experiments presented in this paper continue the line of advanced tokamak (AT) scenario studies at high triangularity in JET by concentrating on the characterization of the edge pedestal and the ELM behaviour with deuterium and/or light impurity fuelling (neon, nitrogen). Both injection of extrinsic impurities and D2 puffing are shown to have a significant impact on the edge pedestal in typical JET AT conditions. The ELM energy loss, ΔWELM/Wdia, can be reduced to below 3% and the maximum ELM penetration depth can be limited to r/a > 0.7, thus enhancing the possibility for sustainable internal transport barriers at large plasma radius. These conditions can be achieved in two separate domains, either at a radiated power fraction (Frad) of 30% or at a fraction of >50%. At the lower Frad the ELMs are type I and a high pedestal pressure is maintained, but the occasional large ELM may still occur. At Frad > 50% the pedestal pressure is degraded by 30–50%, but the ELMs are degraded to type III. The intermediate regime at Frad ∼ 40% is unattractive for ITB scenarios because large type I ELMs occur intermittently during the predominantly type III ELM phases (compound type I/III). Frad = 30% can be obtained with D2 fuelling alone, whereas neon or nitrogen seeding is needed to achieve Frad > 50%. Only a limited number of tests have been carried out with nitrogen seeding, with the preliminary conclusion that the plasma edge behaviour is similar to that with neon seeding once the radiated fraction is matched.