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Pedestal and ELM response to impurity seeding in JET advanced scenario plasmas

机译：JET高级场景等离子体中的基座和ELM对杂质注入的响应

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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 D_2 puffing to reduce heat fluxes.rnThe 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 D_2 puffing are shown to have a significant impact on the edge pedestal in typical JET AT conditions. The ELM energy loss, △W_(ELM)/ W_(dia), 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 (F_(rad)) of 30% or at a fraction of > 50%. At the lower F_(rad) the ELMs are type I and a high pedestal pressure is maintained, but the occasional large ELM may still occur. At F_(rad) > 50% the pedestal pressure is degraded by 30-50%, but the ELMs are degraded to type III. The intermediate regime at F_(rad) ～ 40% is unattractive for ITB scenarios because large type I ELMs occur intermittently during the predominantly type III ELM phases (compound type I/III). F_(rad) = 30% can be obtained with D_2 fuelling alone, whereas neon or nitrogen seeding is needed to achieve F_(rad) > 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.
机译：高级方案等离子体必须经常在低密度和高功率下运行，从而导致热边缘温度以及随之而来的等离子体表面相互作用区域的功率处理问题。 JET的实验通过探索使用外部杂质注入和D_2膨化来减少热通量来解决此问题。rn本文中的实验通过专注于表征在JET的高三角形性条件下继续进行高级托卡马克（AT）情景研究。氘和/或轻杂质（氖，氮）加注时的边缘基座和ELM行为。在典型的JET AT条件下，外来杂质的注入和D_2的膨化都对边缘基座有重大影响。 ELM能量损失△W_（ELM）/ W_（dia）可以降低到3％以下，并且最大ELM穿透深度可以限制为r / a> 0.7，从而提高了内部可持续运输障碍的可能性等离子半径。这些条件可以在两个单独的域中实现，或者以30％的辐射功率分数（F_（rad））或> 50％的分数实现。在较低的F_（rad）下，ELM为I型，并保持了较高的基座压力，但偶尔仍可能会出现较大的ELM。在F_（rad）> 50％时，基座压力降低30-50％，但ELM降级为III型。 F_（rad）〜40％的中间状态对于ITB场景没有吸引力，因为大型的I型ELM在主要的III型ELM阶段（化合物I / III型）间歇地发生。仅使用D_2燃料即可获得F_（rad）= 30％，而要达到F_（rad）> 50％，则需要进行氖气或氮气播种。氮注入仅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注入相似。

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