托卡马克边缘湍流动量输运驱动极向旋转的实验研究

Plasma poloidal mass flows are of great interest for their contribution to shearing and to the trigger mechanism for edge and core transport barriers. Experimental results demonstrate a spin-up of main ion poloidal rotation at the transition from L mode to H mode. Theoretical works indicate that turbulent momentum transport, especially the non-diffusive stress is a promising candidate for explaining the origin of poloidal rotation in plasma edge. However, it remains to be validated experimentally on tokamaks. The research in this project will be based on the HL-2A tokamak. By utilizing Langmuir probe, Doppler backward scattering reflectometer system and beam emission spectroscopy, the evolution of edge poloidal rotation can be measured. The deviation of the poloidal rotation from neoclassical prediction by the turbulent Reynolds stress can be obtained. The decomposition of Reynolds stress, i.e. diffusive stress, convection stress and residual stress can be distinguished respectively. The dependence of turbulence-driven rotation torque on adiabatic parameter can be obtained. The correlation between shearing flow and dominant turbulent modes will be studied. These works are of great importance for understanding the physical connection between turbulent transport and rotation drive. They are beneficial to the performance improvement of ITER and reactor-like fusion devices in the future, especially in relation to enhanced confinement.

在磁约束核聚变中，等离子体极向旋转及其剪切对触发边缘输运垒和实现低约束模向高约束模的转换（L-H转换）具有至关重要的作用。寻找等离子体边缘极向旋转的动量来源成为国际上亟待解决的热点物理问题。理论研究表明，由背景湍流引起的非扩散对流动量输运对驱动极向旋转具有关键作用。目前，托卡马克上关于该物理过程的实验研究非常欠缺。本项目依托HL-2A装置，结合静电探针、多普勒反射计及最新发展的束发射光谱诊断，测量边缘极向速度的剖面演化，获得其相对于新经典理论预测的偏离，对比分析湍流雷诺胁强各项——扩散项、对流项及剩余胁强项对其贡献。进一步获得由湍流驱动的旋转力矩对绝热参数的依赖关系，研究极向剪切流与主导湍流模式的关联性。本项目的开展有益于揭示边缘湍流动量输运驱动极向旋转的物理机制，为提高ITER及未来聚变装置的约束性能提供有效的实验基础。

本项目依托HL-2A托卡马克装置，开展了边缘湍流动量输运驱动极向旋转的实验研究。发现了极向速度的实验测量值明显偏离新经典理论预测，验证了边缘湍流引起的反常动量输运是造成极向速度偏离的主要原因。获得了边缘湍流动量输运中的雷诺胁强、扩散项及对流项，计算给出了剩余胁强项及其径向负梯度表征的极向旋转力矩。研究表明，漂移波湍流的谱对称性破缺的演化与极向旋转力矩的发展具有很好的一致性。湍流胁强从压力梯度中的自由能获得能量，通过漂移波湍流谱的对称性破缺产生有限的剩余胁强，从而驱动极向旋转的产生。研发发现，加热功率升高时，湍流动量输运对极向旋转的驱动增强；密度增加时，等离子体响应由绝热向流体动力学转变，密度扰动与电势扰动的耦合降低，导致了湍流动量输运对极向旋转的驱动减弱。这些研究结果证明了湍流动量输运是等离子体边缘极向旋转的动量来源，有利于为磁约束聚变装置中观察到的等离子体旋转变化及影响输运的现象提供物理图像，为提高ITER及未来聚变堆的约束性能提供物理基础。