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Zonal flow production in the L-H transition in Alcator C-Mod

机译：Alcator C-Mod的L-H过渡区中的区域流生产

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摘要

Transitions of tokamak confinement regimes from low- to high-confinement are studied on Alcator C-Mod (Hutchinson et al 1994 Phys. Plasmas 1 1511) tokamak using gas-puff-imaging, with a focus on the interaction between the edge drift-turbulence and the local shear flow. Results show that the nonlinear turbulent kinetic energy transfer rate into the shear flow becomes comparable to the estimated value of the drift turbulence growth rate at the time the turbulent kinetic energy starts to drop, leading to a net energy transfer that is comparable to the observed turbulence losses. A corresponding growth is observed in the shear flow kinetic energy. The above behavior is demonstrated across a series of experiments. Thus both the drive of the edge zonal flow and the initial reduction of turbulence fluctuation power are shown to be consistent with a lossless kinetic energy conversion mechanism, which consequently mediates the transition into H-mode. The edge pressure gradient is then observed to build on a slower (1 ms) timescale, locking in the H-mode state. These results unambiguously establish the time sequence of the transition as: first the peaking of the normalized Reynolds power, then the collapse of the turbulence, and finally the rise of the diamagnetic electric field shear as the L-H transition occurs.
机译：在Alcator C-Mod（Hutchinson et al 1994 Phys.Plasmas 1 1511）托卡马克上使用气体吹扫成像研究了托卡马克限制机制从低约束到高约束的转变，重点是边缘漂移湍流之间的相互作用。和局部剪切流。结果表明，在湍流动能开始下降时，非线性湍动能传递到剪切流中的速率与漂移湍流增长率的估计值相当，从而导致净能量传递与观察到的湍流相当损失。在剪切流动能中观察到相应的增长。通过一系列实验证明了上述行为。因此，边缘地带流的驱动和湍流波动功率的初始减小都与无损动能转换机制相一致，从而转换为H模式。然后观察到边缘压力梯度建立在较慢的（1 ms）时间刻度上，并锁定在H模式状态。这些结果明确地将转变的时间序列确定为：首先是归一化雷诺功率的峰值，然后是湍流的崩溃，最后是随着L-H转变而产生的反磁场剪切力的上升。

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