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Pedestal evolution physics in low triangularity JET tokamak discharges with ITER-like wall

机译：具有ITER形壁的低三角形JET托卡马克放电的基座演化物理学

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摘要

The pressure gradient of the high confinement pedestal region at the edge of tokamak plasmas rapidly collapses during plasma eruptions called edge localised modes (ELMs), and then re-builds over a longer time scale before the next ELM. The physics that controls the evolution of the JET pedestal between ELMs is analysed for 1.4 MA, 1.7 T, low triangularity, δ - 0.2, discharges with the ITER-like wall, finding that the pressure gradient typically tracks the ideal magneto-hydrodynamic ballooning limit, consistent with a role for the kinetic ballooning mode. Furthermore, the pedestal width is often influenced by the region of plasma that has second stability access to the ballooning mode, which can explain its sometimes complex evolution between ELMs. A local gyrokinetic analysis of a second stable flux surface reveals stability to kinetic ballooning modes; global effects are expected to provide a destabilising mechanism and need to be retained in such second stable situations. As well as an electron-scale electron temperature gradient mode, ion scale instabilities associated with this flux surface include an electro-magnetic trapped electron branch and two electrostatic branches propagating in the ion direction, one with high radial wavenumber. In these second stability situations, the ELM is triggered by a peeling-ballooning mode; otherwise the pedestal is somewhat below the peeling-ballooning mode marginal stability boundary at ELM onset. In this latter situation, there is evidence that higher frequency ELMs are paced by an oscillation in the plasma, causing a crash in the pedestal before the peeling-ballooning boundary is reached. A model is proposed in which the oscillation is associated with hot plasma filaments that are pushed out towards the plasma edge by a ballooning mode, draining their free energy into the cooler plasma there, and then relaxing back to repeat the process. The results suggest that avoiding the oscillation and maximising the region of plasma that has second stability access will lead to the highest pedestal heights and, therefore, best confinement-a key result for optimising the fusion performance of JET and future tokamaks, such as ITER.
机译：托卡马克等离子边缘的高限制基座区域的压力梯度在等离子爆发期间迅速塌陷，称为边缘局部模式（ELM），然后在下一个ELM之前的较长时间范围内重建。分析了控制ELM之间的JET基座演变的物理过程，分析了1.4 MA，1.7 T，低三角形，δ-0.2，并通过ITER状壁放电，发现压力梯度通常跟踪理想的磁流体动力膨胀极限，与动态气球模式的作用一致。此外，基座宽度通常受等离子体区域的影响，该区域具有进入膨胀模式的第二稳定性，这可以解释其有时在ELM之间的复杂演化。对第二个稳定通量表面的局部动力学分析显示出对动态膨胀模式的稳定性。预期全球影响将提供破坏稳定的机制，需要在这种第二稳定的情况下予以保留。除了电子级电子温度梯度模式外，与此通量表面相关的离子级不稳定性还包括一个电磁陷阱电子分支和两个在离子方向上传播的静电分支，其中一个具有高径向波数。在这些第二种稳定情况下，ELM由剥离气球模式触发；否则，在ELM发生时，基座略低于剥离-膨胀模式的边缘稳定性边界。在后一种情况下，有证据表明，较高频率的ELM受到等离子体振荡的影响，从而导致在达到剥离气球边界之前基座发生碰撞。提出了一种模型，其中振荡与热等离子体灯丝相关，该热等离子体灯丝通过膨胀模式推向等离子体边缘，将其自由能排入那里的较冷等离子体中，然后放松以重复该过程。结果表明，避免振荡并最大化具有第二次稳定通道的血浆区域将导致最高的基座高度，因此，最佳的封闭性是优化JET和未来托卡马克（如ITER）融合性能的关键结果。

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  • 来源
    《Nuclear fusion》 |2018年第1期|016021.1-016021.17|共17页
  • 作者

    C. Bowman; D. Dickinson; L. Horvath; A.E. Lunniss; H.R. Wilson; I. Cziegler; L. Frassinetti; K. Gibson; A. Kirk; B. Lipschultz; C.F. Maggi; CM. Roach; S. Saarelma; P.B. Snyder; A. Thornton; A. Wynn;

  • 作者单位

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom,CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom,CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom;

    Association VR, Fusion Plasma Physics, KTH, SE-10044 Stockholm, Sweden;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom;

    CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom;

    CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

    CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

    CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

    General Atomics, PO Box 85608, San Diego, CA 92186-5608, United States of America;

    CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

    York Plasma Institute, Department of Physics, University of York, Heslington, York YO10 5DD, United Kingdom,CCFE, Culham Science Centre, Abingdon OX14 3DB, United Kingdom;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

    pedestal; ELMs; JET; stability;

    机译：基座ELMs;喷射;稳定性;

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