湍流与磁岛多尺度耦合对等离子体输运和稳定性影响的实验研究

Both anomalous electron thermal transport and disruptive instabilities are critical to both the access and the sustainment of tokamak burning plasmas. Reducing both microturbulent level and the width of magnetic island are thought to contribute to improving anomalous electron thermal transport and avoiding plasma disruptions, respectively. These can thus promote both the stability and performance for tokamak plasma long-pulse operation. Recent published papers in theories and simulations suggest that magnetic island can regulate microturbulence to influence anomalous electron thermal transport, and the width of magnetic island was also found to be closely related to microturbulence. However, experimental research in this area is preliminary, and very few experimental publications that we are aware of give the quantitative study of its impact on electron thermal transport as well as the exploration of microturbulent impact on the width of magnetic island. In this proposal, we will carry out experiments in the EAST superconducting tokamak. Through using the combination of some diagnostics to measure turbulence (CO2 laser collective scattering, Doppler background scattering, correlation Electron cyclotron emission and so on), some diagnostics to measure equilibrium profiles with high temporal-spatial resolution and several codes, i.e., TRANSP, GS2, GTS and so on, we will focus on quantitative study of electron thermal transport due to microturbulence-magnetic island interaction, as well as the exploration of microturbulent impact on the width of magnetic island. This can help to broaden parameters range during plasma operation so as to contribute to steady-state operation of long-pulse burning plasma discharges for ITER and future magnetic confinement fusion reactors.

反常电子热输运和破裂不稳定性是托卡马克等离子体实现燃烧和维持长脉冲运行的俩大关键性物理问题。降低湍流水平和磁岛宽度分别被认为有助于改善电子热输运和防止破裂，从而提高托卡马克等离子体长脉冲运行的性能及稳定性。最近的理论模拟研究成果表明：磁岛可通过调节湍流来影响电子热输运，且磁岛宽度也与湍流密切相关。但该方面实验研究还比较初步，鲜有实验定量研究湍流与磁岛多尺度耦合对电子热输运的影响以及展开湍流影响磁岛宽度的探索。本项目将依托于有长脉冲运行能力的EAST装置，借助于CO2激光相干散射、多普勒背散射及相关电子回旋辐射等湍流测量诊断、高时空分辨平衡剖面测量诊断和TRANSP、GS2及GTS等程序，定量研究湍流(尤其电子模湍流)与磁岛耦合对电子热输运的影响，并探索湍流对磁岛宽度影响的机制。这将有助于拓宽托卡马克实验运行参数区间，为未来ITER及聚变反应堆长脉冲高性能等离子体稳定运行提供线索和数据积累。

未来聚变电站需要等离子体自持燃烧且长脉冲稳定运行。自持燃烧所需能量主要依赖于其自生的阿尔法粒子，它主要加热电子的性质决定了等离子体以电子热输运为主，必须研究驱动电子热输运的微观湍流的特性。此外，燃烧等离子体具有相对较高的比压，不可避免会激发一些有磁岛的宏观磁流体模不稳定性，过宽的磁岛会导致等离子体破裂且影响电子热输运。探索湍流与宏观磁流体模的多尺度耦合效应不但对于理解并最终控制反常电子热输运重要，而且对未来磁约束聚变装置等离子体长脉冲稳定运行重要。依托于先进的EAST等托卡马克的实验平台，借助于可以同时观测到湍流和宏观磁流体模的相干散射诊断，我们系统的开展了湍流特性及其与宏观磁流体模多尺度相互作用的实验及湍流回旋动理学数值模拟研究。我们实验证明了k=8-30 cm^-1范围内的湍流与等离子体能量约束高度相关；我们也发现2/1新经典撕裂模磁岛可以显著影响电子尺度湍流的频率和功率，并可以在很宽的频率范围内与湍流发生多尺度非线性耦合，进一步的GS2回旋动理学模拟研究结果定性解释了磁岛存在前后湍流变化的实验观测。此外，我们还拓展研究了能量约束改善时湍流的行为特征、研究了湍流与低频流以及阿尔芬本征模的多尺度物理过程。本项目研究成果可为未来聚变反应堆如CFETR等装置的长脉冲、高性能稳定运行提供重要的科学参考和数据积累。