EAST边界磁拓扑改变条件下钨杂质聚芯抑制的机理研究

Tungsten has been selected as the material for divertor-plate in next generation fusion devices, ITER, since its high melting point and low sputtering rate. However, impurity accumulation always occurs if tungsten is transported from divertor target to plasma core, resulting in degradation of confinement performance or plasma disruption. Suppression of impurity tungsten accumulation in the core region is one of the most challenges for ITER to achieve steady-state high-performance operation. Resonant magnetic perturbation (RMP) can effectively induce edge magnetic topology distortion in tokamaks, which would enhance the impurity screening effect in the edge region, is a possible alternative method to suppressing impurity tungsten accumulation. This project, based on EAST’s current capabilities and characteristics, aims at the international front of impurity transport study and focuses on the urgent necessity for the steady-state operation of EAST and ITER. By utilizing the extreme ultraviolet spectroscopy diagnostics and impurity transport simulation, to study suppression of impurity tungsten accumulation and its physical mechanism with edge magnetic topology change. The relation between impurity transport coefficient and RMP and plasma parameters would be studied for the purpose to achieve the suppression of impurity tungsten accumulation in the EAST and ITER. These researches are of significant importance for the effective reduction of impurity tungsten density in the core region while maintaining the steady-state operations for high-performance plasmas.

下一代聚变装置ITER采用了能承受高热负荷、低溅射率的金属钨作为偏滤器靶板材料。然而钨作为高Z金属，一旦通过输运进入芯部区域极易发生钨杂质聚芯，严重影响等离子体约束性能甚至引发破裂。如何抑制钨杂质聚芯是ITER实现高性能稳态运行所面临的一个重要挑战。共振磁扰动（RMP）可以有效改变托卡马克边界磁拓扑，增强边界区域的杂质屏蔽效应，是一条抑制钨杂质聚芯的可能的新途径。本项目瞄准钨杂质输运研究领域的国际前沿，立足EAST全超导托卡马克现有能力与特色，紧紧围绕EAST与ITER实现稳态运行的迫切需要，结合极紫外光谱诊断与杂质输运模拟计算，通过分析杂质输运系数与RMP参数及等离子参数的依赖关系，研究边界磁拓扑改变条件下钨杂质聚芯抑制的物理机制,进而对ITER上钨杂质聚芯的抑制提供必要参考。该研究对于有效降低托卡马克芯部钨杂质含量，维持高性能稳态运行具有重要意义。

未来聚变堆多采用钨作为偏滤器靶板材料。然而钨作为高Z金属，一旦通过输运进入芯部区域极易发生钨杂质聚芯，严重影响等离子体约束性能甚至引发破裂。如何抑制钨杂质聚芯是ITER实现高性能稳态运行所面临的一个重要挑战。共振磁扰动（RMP）可以有效改变托卡马克边界磁拓扑，增强边界区域的杂质屏蔽效应，是一条抑制钨杂质聚芯的可能的新途径。本项目依托EAST 全超导托卡马克实验平台，通过发展杂质光谱系统，开展了杂质输运物理实验研究和杂质输运模拟计算研究，探索了RMP控制芯部杂质的物理机制研究。经过为期三年的研究，目前已经完成了EAST装置上的杂质光谱诊断系统性能升级，并按照计划在EAST上开展了RMP控制杂质的物理实验通过优化实验方案，提升了RMP对钨杂的抑制效果。通过开展模拟计算研究，得到钨杂质输运系数与RMP位型以及主要等离子体参数依赖关系，并分析了RMP实现钨杂质控制的物理机制。发现在RMP作用条件下，边界杂质离子的扩散系数要显著高于主离子的扩散系数，为RMP实现重杂质控制提供了机理解释。此外，计算结果也也验证了RMP实现重杂质控制与主离子约束之间的兼容性，为未来聚变堆上采用RMP进行重杂质控制提供了理论依据。本研究可以为未来ITER和聚变堆实现稳态高性能运行提供有价值的参考。