Bifurcation of quiescent H-mode to a wide pedestal regime in DIII-D and advances in the understanding of edge harmonic oscillations
Bifurcation of quiescent H-mode to a wide pedestal regime in DIII-D and advances in the understanding of edge harmonic oscillations
复制标题
DIII-D 中静态 H 模式的分岔到宽基座区域以及边缘谐波振荡的理解进展
DOI：
10.1088/1741-4326/aa7531
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发表时间：
2017
期刊：
影响因子：
3.3
通讯作者：
Zheng Yan
中科院分区：
文献类型：
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作者：
Xi Chen;K. Burrell;T. Osborne;K. Barada;N. Ferraro;A. Garofalo;R. Groebner;G. McKee;C. Petty;M. Porkolab;T. Rhodes;J. Rost;P. Snyder;W. Solomon;Zheng Yan
对常规静态h模（qh模）边缘调节的相干边缘谐波振荡（EHO）进行了新的实验研究和建模，验证了边缘旋转剪切破坏低n扭结剥离模式作为EHO的附加驱动机制的假设。观测到的EHO所需的最小边缘E × B剪切量随着台座碰撞νe∗而线性减小，这有利于在低碰撞和低旋转的机器（如ITER）中运行qh模式。此外，最近发现DIII-D中的qh模式在双零形等离子体的低扭矩下分叉成新的“宽基座”状态，其特点是基座高度、宽度和热能限制增加（Burrell 2016 Phys）。等离子体23 056103；融合57 022007)。这可能为在低扭矩下实现高性能elm稳定运行提供了另一种途径，除了低扭矩qh模式在应用3D油田中持续运行之外。在“宽基座”上观察到多分支低k和中k湍流。新的实验支持这样的假设，即减小的边缘E × B剪切使宽带湍流不稳定，从而放松边缘压力梯度，提高剥离-气球稳定性，并允许更宽、更高的基座。能够准确预测EHO的临界E × B剪切，并在低扭矩下保持高性能的qh模式，是将qh模式运行投射到ITER和未来机器的基本要求。
New experimental studies and modelling of the coherent edge harmonic oscillation (EHO), which regulates the conventional Quiescent H-mode (QH-mode) edge, validate the proposed hypothesis of edge rotational shear in destabilizing the low-n kink-peeling mode as the additional drive mechanism for the EHO. The observed minimum edge E × B shear required for the EHO decreases linearly with pedestal collisionality νe∗, which is favorable for operating QH-mode in machines with low collisionality and low rotation such as ITER. In addition, the QH-mode regime in DIII-D has recently been found to bifurcate into a new ‘wide-pedestal’ state at low torque in double-null shaped plasmas, characterized by increased pedestal height, width and thermal energy confinement (Burrell 2016 Phys. Plasmas 23 056103, Chen 2017 Nucl. Fusion 57 022007). This potentially provides an alternate path for achieving high performance ELM-stable operation at low torque, in addition to the low-torque QH-mode sustained with applied 3D fields. Multi-branch low-k and intermediate-k turbulences are observed in the ‘wide-pedestal’. New experiments support the hypothesis that the decreased edge E × B shear enables destabilization of broadband turbulence, which relaxes edge pressure gradients, improves peeling-ballooning stability and allows a wider and thus higher pedestal. The ability to accurately predict the critical E × B shear for EHO and maintain high performance QH-mode at low torque is an essential requirement for projecting QH-mode operation to ITER and future machines.