Research of the interaction among different spatio-temporal scale turbulence and transport structure

基于托卡马克等热核聚变等离子体中各种显著结构是由不同时空尺度涨落之间的复杂相互作用形成的观点，研究了湍流输运过程中相互作用的基本原理。1）基于理论和回旋流体模型的模拟，阐明了微尺度电子温度梯度（ETG）湍流非线性相互作用产生的纬向流的动力学及其结构。我们研究了湍流涨落与纬向涨落之间的一个“分配律”，发现这种分配是由磁剪切控制的。具体地说，我们发现在弱的和/或反向的磁剪切等离子体中，大部分的涨落能量在高压梯度区被有效地转移到纬向涨落上，从而湍流输运的不稳定性消失 ...更多信息 在上述过程（1）中对宏观尺度离子温度梯度（ITG）湍流传输进行了观察，并发现在ITG临界梯度附近的热扩散率中表现出间歇行为。这可能是由于ITG湍流、ITG驱动的带状流以及微尺度ETG驱动的带状流之间的复杂相互作用造成的。结果表明，在宽波数和频率空间同时处理不同时空尺度的关键物理过程是重要的。3）为了阐明次生大尺度对流结构与母体湍流结构之间的关系，我们发展了调制不稳定性分析，发现湍流结构对对流结构有显著影响。也就是说，带状流优先从径向伸长的湍流结构中激发，而流光从极轴向伸长的湍流结构中产生。因此，次级大尺度结构是由母体的双稳结构所控制的。4）为了描述湍流分量和纬向分量混合的输运动力学，我们研究了概率分布函数（PDF）、分维、小波谱、双相干、等离子体中的分形维数在纬向流的控制下显著降低，这表明被抑制的输运是由相当相干的过程维持的。少

Based on the idea that various prominent structures in thermonuclear fusion plasmas like tokamak are established resulting from complex interaction among different spatio-temporal scale fluctuations, we studied fundamental principles of the interaction in turbulent transport process. The main results are as follows :1) Based on theory and simulation using gyro-fluid model, we clarified the dynamics of zonal flows and its structures produced by nonlinear interaction of micro-scale electron temperature gradient (ETG) turbulence. We investigated a "partition law" between turbulent fluctuation and zonal fluctuation and found that the partition is controlled by magnetic shear. Specifically, we found that in weak and/or reversed magnetic shear plasmas a large portion of fluctuation energy is efficiently transferred to zonal fluctuation in high pressure gradient regime and then anomalousness of turbulent transport disappears.2) We studied the effects of the micro-scale ETG-driven zonal flows … More observed in the above process (1) on macro-scale ion temperature gradient (ITG) turbulent transport and found that an intermittent behavior is exhibited in the heat diffusivity near the ITG critical gradient. This may results from complex interplay among ITG turbulence, ITG-driven zonal flow and also micro-scale ETG-driven zonal flow. The result indicates that treating key physical processes with different spatio-temporal scales in wide wave number and frequency space simultaneously is important.3) In order to clarify the relation between secondary generated large scale convective structure and structure of maternal turbulence, we developed a modulational instability analysis and found that the convective structure is significantly influenced by the structure of turbulence. Namely, zonal flows are preferentially excited from radially elongated turbulence structure, whereas streamers are produced from poloidally elongated turbulence structure. Thus, the secondary large scale structure is found to be controlled by the structure of maternal turbulence.4) In order to characterize the transport dynamics where the turbulent component and zonal component are mixed, we investigated statistical quantities such as probability distribution function (PDF), fractal dimension, wavelet spectrum, bi-coherence, etc. We found that the fractal dimension is significantly reduced in plasmas dominated by zonal flows, suggesting that the suppressed transport is sustained by rather coherent process. Less