J-TEXT托卡马克上边界湍流特性对高密度运行影响的实验研究

Both the requirements of decreasing the heat load on the first wall and increasing the fusion output power, determine that the future tokamak reactor must be operated at high density condition. However currently, there exist some problems for the tokamak high density operating, such as the degradation of confinement, occurrence of radiative-thermal instability. Sometimes it even induces macro-MHD instabilities and density limit disruption. It is known that the edge cooling is critical, and turbulent transport is the dominant channel for edge cooling. Therefore, this project proposes to study the influence of turbulence properties at edge on high density operation experimentally on J-TEXT tokamak. We will firstly experimentally study the evolution of edge turbulence-zonal flow system with density increasing. Then, combining with codes such as BOUT++, this project plans to ascertain the sort of the turbulence which managing the edge transport in high density plasma, to study the nonlinear interaction between the objective turbulence and zonal flow, and to analyze the mechanism of edge transport increasing. Finally, this project aims to explore the effects of turbulence properties at edge on high density operation, by using the electrode biasing and resonant magnetic perturbation to modulate the edge turbulence and transport. These results will help to understand the turbulence and transport at edge in tokamak and provide reference for the high-density operation strategy of the future fusion reactor.

降低第一壁热负荷和提高聚变输出功率两方面的需求，都决定了未来托卡马克聚变堆必须运行在高密度等离子体条件下。但是目前托卡马克高密度运行仍面临一些问题，比如约束的下降、辐射热不稳定性的出现，甚至具有引发宏观磁流体不稳定性和密度极限密度破裂的风险。研究表明，边界冷却是其中的关键，而湍流输运是边界冷却的主要通道。据此，本课题拟基于J-TEXT托卡马克，针对边界湍流特性对托卡马克高密度运行的影响，开展实验研究。首先从实验上观测边界湍流-带状流系统随等离子体密度的演化；再结合BOUT++等模拟工具，确定在高密度等离子体中主导边界输运的湍流模式，并研究目标湍流与带状流之间的非线性相互作用，分析输运的增长机制；最后，利用偏压电极、共振磁扰动等手段对边界湍流进行调制，研究湍流特性的变化对高密度运行的影响。项目的执行可加深对托卡马克边界湍流输运的理解，为未来聚变堆的高密度运行控制策略提供参考。

在诊断方面，本项目在J-TEXT托卡马克上完成了双色HCN激光相干散射仪诊断系统的搭建，该系统有3道测量，可以观测波数分别为2cm-1, 7cm-1和12cm-1的芯部湍流。通过此系统，我们观测到了边界偏压电极对湍流和速度的调制作用。此外，本项目还升级了J-TEXT上原有的三色偏振干涉仪系统，将系统的空间分辨率从3cm提升至1.5cm，从而实现了更高精度的电子密度和电流密度剖面反演。.在实验研究方面，本项目在J-TEXT上全面地研究了密度极限破裂放电中的边界湍流和输运行为。通过前向散射和静电探针系统发现边界电场剪切的崩塌和湍流输运的增强是导致密度极限破裂的主要原因。输运增强会降低边界等离子体温度，从而激发的HFSHD现象，继而引起撕裂模和大破裂。这些实验结果揭示了托卡马克上密度极限破裂的整个发展过程，并且首次说明了边界湍流输运和HFSHD之间的关系，能够提高大家对托卡马克中密度极限现象的理解与认识。.此外，本项目首次使用偏压电极系统实现了对密度极限的提升。实验发现，偏压电极通过提升边界电场剪切降低了湍流输运水平，从而实现了密度极限的提升，这个实验结果进一步揭示了湍流输运在密度极限中的作用机制。