SOC边缘偏置实验中的自组织临界性观察
Observation of self-organized criticality (SOC) behavior during edge biasing experiment on TEXTOR
摘要：
利用TEXTOR托卡马克边缘电极偏置实验前和偏置过程中等离子体边缘和刮除层的涨落数据，研究了边缘等离子体输运的自组织临界性（SOC）行为。在偏置之前的“非剪切”放电阶段，电势和密度波动都清楚地表现出与SOC相关的一些特性：（1）在频谱中存在f-1幂律依赖性，（2）自相关函数中缓慢衰减的长尾，（3）在所有检测到的径向位置处Hurst参数值大于0.5，（4）涨落的非高斯PDF和（5）边缘等离子体区域中类雪崩事件的径向传播。在偏置阶段，与生成的边缘径向电场Er，因此剪切ErxB流，局部湍流被发现是很好的解相关的ErxB速度剪切，与理论预测一致。然而，它是伴随着发现，赫斯特参数显着增强，在负流动剪切区和刮除层，以及，这是相反的理论预期。这些意见，我们的理解等离子体传输机制的影响进行了讨论。
英文摘要：
The self-organized criticality (SOC) behavior of the edge plasma transport has been investigated using the fluctuation data measured in the plasma edge and the scrape-off layer of TEXTOR tokamak before and during the edge electrode biasing experiments. In the "nonshear" discharge phase before biasing, both the potential and density fluctuations clearly exhibit some of the characteristics associated with SOC: (1) existence of f -1 power-law dependence in the frequency spectrum, (2) slowly decaying long tails in the autocorrelation function, (3) values of Hurst parameters larger than 0.5 at all the detected radial locations, (4) non-Gaussian PDF of fluctuations and (5) radial propagation of avalanche-like events in the edge plasma area. During the biasing phase, with the generation of an edge radial electric field Er and hence a sheared ErxB flow, the local turbulence is found to be well decorrelated by the ErxB velocity shear, consistent with theoretical predictions. Nevertheless, it is concomitantly found that the Hurst parameters are substantially enhanced in the negative flow shear region and in the scrape-off layer as well, which is contrary to theoretical expectation. Implication of these observations to our understanding of plasma transport mechanisms is discussed.
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