托卡马克封闭偏滤器等离子体物理问题模拟研究

Investigation of divertor becomes one the most important issues in the magnetic confined fusion research. Control of heat flux and erosion at plasma-facing components (PFC), especially, at divertor target plates, is a major issue for design and operation of next-step high-power steady-state fusion devices. This necessitates the achievement of highly dissipative or detached divertor conditions to reduce both the heat flux and divertor plasma temperature to suppress sputtering at the plasma facing material surface. Strong neutral baffling, i.e. closure of the divertor, is recognized as an effective path for optimization of the divertor geometry. It is expected that increase closure will improve the gas pressure in the divertor, thus increase heat radiative dissipation and also pumping efficiency. However, because (a) there are complicated nonlinear processes in the closed divertor, (b) it is very expensive to rebuild a new divertor, and (c) the closed geometry makes diagnosis much more difficult, the divertor closure plasma physics has not been fully assessed and understood. In this project, the 2D edge plasma code SOLPS as well as 2PMF tool will be applied to simulate and analyze the plasma physics in the closed divertor. The project includes five parts: 1. investigation of plasma physics mechanism in closed divertor; 2. pumping study in closed divertor; 3. driving mechanism of scrape-off layer plasma flow; 4. the impurity screening and downstream-upstream plasma compatibility of the closed divertor tokamak; 5. the fuel retention in the closed divertor during different discharge operation. From this project, we expect to: understand the basic plasma physics in the closed divertor; investigate the possibility of the application of a closed divertor in the future reactor; and provide idea for the divertor design and optimization.

偏滤器已经成为制约磁约束可控核聚变发展的最主要问题之一，如何控制沉积到偏滤器靶板的能流密度和等离子体温度，是研究偏滤器等离子体的最关键问题。通过优化设计偏滤器形状来改变其封闭性，以提高偏滤器的能量辐射效率，从而在较低上游等离子体密度条件下实现脱靶，为聚变堆偏滤器热负荷和靶板侵蚀控制提供了一个重要思路。封闭偏滤器等离子体中涉及到复杂的非线性行为，且实验改造昂贵、诊断复杂，尚有许多问题亟待解决。本项目针对封闭偏滤器等离子体中存在的主要问题，采用边界等离子体模拟程序SOLPS，结合理论分析开展五方面研究：1.封闭偏滤器等离子体物理机理研究；2.封闭偏滤器抽气研究；3.刮削层等离子体流驱动机制研究；4.封闭偏滤器上下游等离子体兼容性研究；5.燃料在封闭偏滤器的滞留研究。通过本项目，理解封闭偏滤器基本物理行为，探索其用于未来聚变堆的可行性，为未来偏滤器的设计提供理论依据和指导方向。

本项目针对封闭偏滤器等离子体的关键物理问题，采用二维边界等离子体程序SOLPS开展了相关研究。主要内容分为五部分（1）封闭偏滤器物理：发现提高偏滤器封闭性有助于中性粒子聚集，从而增大等离子体与中性粒子碰撞，提高偏滤器封闭性，促进脱靶的实现。（2）封闭偏滤器抽气：粒子排除和能量耗散是相冲突的，抽气会影响中性粒子行为，提高脱靶密度阈值；有效粒子排除是影响等离子体行为的本质，相同的上游等离子体条件下，相同的有效粒子排除速率会得到相同的偏滤器等离子体参数。（3）刮削层等离子体流：芯部和上游刮削层漂移和粘滞力有助于增强杂质屏蔽能力，降低杂质聚芯。（4）封闭偏滤器和上游等离子体兼容性：偏滤器封闭性会对上游等离子体产生影响，封闭偏滤器可以降低台基区燃料密度，因此增强芯部边界的兼容性。（5）钨偏滤器中燃料的滞留：采用燃料滞留程序HIIPC耦合SOLPS，研究了EAST钨偏滤器中放电条件对燃料滞留的影响，发现脱靶运行模式会提高燃料滞留量。