托卡马克等离子体中的非扩散能量输运实验研究

In tokamak plasmas, the cross-field energy transport generally plays a role of driving energy from the hot area in plasma core region to the cold area in the periphery. Energy transport in tokamak plasmas was historically explained in a diffusive way, in which the diffusive model was applied with assumption that the transport of energy across the magnetic field can be described solely by a diffusion equation. With the aids of off-axis auxiliary heating experiments, it is realized that both conductive (diffusive) transport and convective (non-diffusive) transport are essential parts of energy transport. Convection term becomes an indispensable part of the energy transport equation, which describes the actual physics in plasmas. The calculation of convective velocity is essential for the understanding of mechanism of non-diffusive transport in tokamak plasma. Taken the advantages of EAST facility, this project will conduct experiment and analysis on the topic of non-diffusive energy transport. The research will be focused on the relation between convective velocity and major parameters or the status of plasmas and the mechanism of non-diffusive energy transport. The possibility of improvement on the core plasma confinement will also be discussed when favorable inward non-diffusive energy transport is taken in to account. The implementation of this project is the intensive study for the basic mechanism of energy transport and is also beneficial for ITER plasmas and future fusion plant as well.

托卡马克等离子体中横越磁力线的能量输运行为在总体上扮演着将能量从芯部高温区向边界低温区进行输运的角色。长久以来，针对能量输运问题，人们习惯地用热扩散的方式来理解其物理机制，即假设认为使用纯扩散模型能够很好地描述实际发生的输运物理过程。通过离轴加热实验研究，人们意识到能量输运包括扩散输运和非扩散（对流）输运两个部分，需要在输运方程中增加对流项才能全面地反映能量输运的真实物理过程。研究对流速度成为理解非扩散能量输运在托卡马克等离子体中实际效果和物理机制的核心内容。本项目依托EAST大科学工程装置，计划利用EAST实验平台对非扩散能量输运现象开展实验研究，探索对流速度与主要等离子体参数/状态之间的关联性，分析非扩散能量输运现象的物理机制，探讨利用向内的非扩散能量输运进一步提高芯部等离子体约束性能的可能性。该研究是对能量输运基本机制问题的深入研究，其研究成果对ITER及聚变堆等离子体也有借鉴意义。

本项目的研究围绕如何在托卡马克实验中分析得到非扩散输运信息展开。在本项目的研究工作中，我们分析了EAST实验中高、低密度条件下存在非扩散输运的可能性。根据实验结果，说明EAST实验中在高密度条件下会出现非扩散输运。在低密度下非扩散输运很微弱。研究了SMBI产生的冷脉冲非局域现象中可能存在的非扩散输运。实验证实SMBI冷脉冲所产生的非局域现象是一种非扩散输运，并且与湍流特征的变化密切联系。该湍流特征在极短的时间内变化，不依赖于当地分布参数的改变。我们还对典型EAST等离子体进行了回旋动力学模拟分析，得到主导的湍流模式。模拟说明EAST等离子体的主导湍流模式是低k的CTEM和高k的ETG。已有的理论分析指出CTEM能够驱动向内的能量输运，从而形成宏观的非扩散输运。回旋动理学模拟能够支持实验观察。最后，项目组发展了项目研究需要的弯晶谱仪和电子回旋辐射诊断系统，在EAST上首次可提供同一区域电子温度、密度涨落的同时测量，在EAST实验中发挥重要作用。