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Energy exchange dynamics across L-H transitions in NSTX

机译：NSTX中L-H跃迁之间的能量交换动力学

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摘要

We studied the energy exchange dynamics across the low-to-high-confinement (L-H) transition in NSTX discharges using the gas-puff imaging (GPI) diagnostic. The investigation focused on the energy exchange between flows and turbulence to help clarify the mechanism of the L-H transition. We applied this study to three types of heating schemes, including a total of 17 shots from the NSTX 2010 campaign run. Results show that the edge fluctuation characteristics (fluctuation levels, radial and poloidal correlation lengths) measured using GPI do not vary just prior to the H-mode transition, but change after the transition. Using a velocimetry approach (orthogonal-dynamics programming), velocity fields of a 24 × 30 cm GPI view during the L-H transition were obtained with good spatial (~1 cm) and temporal (~2.5μs) resolutions. Analysis using these velocity fields shows that the production term is systematically negative just prior to the L-H transition, indicating a transfer from mean flows to turbulence, which is inconsistent with the predator-prey paradigm. Moreover, the inferred absolute value of the production term is two orders of magnitude too small to explain the observed rapid L-H transition. These discrepancies are further reinforced by consideration of the ratio between the kinetic energy in the mean flow to the thermal free energy, which is estimated to be much less than 1, suggesting again that the turbulence depletion mechanism may not play an important role in the transition to the H-mode. Although the Reynolds work therefore appears to be too small to directly deplete the turbulent free energy reservoir, order-of-magnitude analysis shows that the Reynolds stress may still make a non-negligible contribution to the observed poloidal flows.
机译：我们使用气吹成像（GPI）诊断研究了NSTX放电中从低到高限制（L-H）过渡的能量交换动力学。研究集中在流动与湍流之间的能量交换，以帮助阐明L-H跃迁的机理。我们将这项研究应用于三种供暖方案，包括NSTX 2010竞选活动的总计17张照片。结果表明，使用GPI测量的边缘起伏特性（起伏水平，径向和多倍相关长度）不仅仅在H模式转变之前发生变化，而是在转变之后发生变化。使用测速方法（正交动力学编程），在L-H过渡期间获得了24×30 cm GPI视图的速度场，具有良好的空间（〜1 cm）和时间（〜2.5μs）分辨率。使用这些速度场进行的分析表明，在L-H过渡之前，生产项在系统上为负，表示从平均流向湍流的转移，这与捕食者－猎物范式不一致。此外，推定生产项的绝对值太小两个数量级，不足以解释观察到的快速L-H跃迁。考虑到平均流中的动能与热自由能之比（估计远小于1），可以进一步加强这些差异，这再次表明湍流耗竭机制可能在过渡过程中不发挥重要作用进入H模式因此，尽管雷诺的工作似乎太小而不能直接耗尽湍流的自由能库，但是数量级分析表明，雷诺应力仍可能对观察到的胶体流做出不可忽略的贡献。

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  • 来源
    《Nuclear fusion》 |2017年第6期|066050.1-066050.12|共12页
  • 作者

    A. Diallo; S. Banerjee; S.J. Zweben; T. Stoltzfus-Dueck;

  • 作者单位

    Princeton Plasma Physics Laboratory, Princeton University, NJ, United States of America;

    Institute for Plasma Research, Bhat, Gandhinagar 382428, Gujarat, India;

    Princeton Plasma Physics Laboratory, Princeton University, NJ, United States of America;

    Princeton Plasma Physics Laboratory, Princeton University, NJ, United States of America;

  • 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

    confinement; L-H transition dynamics; gas-puff-imaging; zonal flows; Reynolds stress;

    机译：禁闭L-H过渡动力学;吹气成像地带流量雷诺应力;

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