托卡马克高极向比压先进运行模式中“远轴”内部输运垒特征及形成机理的研究

In the recent DIII-D/EAST joint experiment, high betap scenario shows the excellent confinement, the compatible feature with fusion reactor plasma on DIII-D. The EAST experiment also proves that this scenario is capable of steady-state long pulse operation. The large-radius (rho≥0.7) internal transport barrier (ITB) is a symbolic feature of this scenario. EAST team will focus on the realization of steady-state long pulse high betap plasma operation on EAST. However, this relies on the physics understanding of the large-radius ITB structure and its formation mechanism. Based on the unsolved physics problems of understanding of the large-radius ITB structure and its formation mechanism in the high betap scenario, this project will systematically investigate the related issues above by both experiment and simulation, taking advantage of experimental and computational capability of DIII-D (US) and EAST (China) facilities. This study will advance the transport physics understanding of high betap scenario. Furthermore, optimizing plasma parameters, we are able to obtain the large-radius ITB on EAST, which would be very beneficial to fulfill the scientific goal of EAST on realizing steady-state high performance operation and even good for the physics design of CFETR.

在最近DIII-D/EAST联合实验中，高极向比压运行模式已经在DIII-D上证明了其优异的性能、与聚变堆等离子体特性相兼容的特性。该运行模式中在较大径向位置（rho≥0.7）出现的内部输运垒，简称为远轴ITB，是其标志性特征。EAST团队的重点研究方向是在实现长脉冲高极向比压等离子体。但这需要对在实验中为等离子体提供高性能保障的远轴ITB物理有较全面且深入的了解。本项目立足于高极向比压运行模式中远轴ITB结构特性及其形成机理这一尚未解决的关键物理问题，依托EAST和DIII-D装置，从实验角度对该运行模式中远轴ITB进行系统、细致的研究，旨在对其结构特性、参数依赖关系等关键问题形成清晰认识，结合模拟，深入理解物理机制，进一步反映高极向比压运行模式的输运物理本质。通过优化参数，在EAST实验中获得远轴ITB，协助EAST实现高性能的科学目标，进而对CFETR物理设计也具有重要的借鉴意义。

在本项目的研究中，项目组通过参加中美联合实验，在美国DIII-D装置上开展高极向比压实验研究，深入分析挖掘DIII-D数据中与远轴内部输运垒（ITB）本身特征有关的线索，总结提炼物理规律。我们分析得到在高极向比压等离子体中主导的湍流模式，并通过杂质气体注入的实验方法实现了对密度远轴ITB的控制。我们完成了对DIII-D远轴ITB形成机制的研究，首次结合实验给出等离子体从第一稳定区移动到第二稳定区进而形成ITB的物理图像。利用以上物理图像，我们完成了EAST高极向比压等离子体的模拟分析，得出限制EAST等离子体性能的主要物理因素是离子温度梯度不稳定性，并结合模拟，提出实现远轴ITB的若干解决方案。同时，项目组发展了EAST上的锂束诊断系统，能够在实验中提供密度分布和密度涨落实验数据，为在EAST上开展相关实验研究提供了基础。