EAST钨铜偏滤器靶板杂质溅射及燃料再循环研究

Fusion machine with tungsten wall has to be presented with the vital issue of poor compatibility of plasma with tungsten. In addition, low fuel retention in tungsten wall, compared with carbon wall, could bring about a different boundary fuel retention feature, thus affecting the ELM(Edge Localized Mode) characteristic in high confinement plasma. EAST has, for the first time in the world, adopted the W/Cu plasma facing components with ITER-like monoblock structure as divertor target plane to withstand the highest heat load. It is a major challenge for EAST to achieve high performance long pulse plasma with a full tungsten divertor. One of the keys in that depends on the thorough understanding and effective control of plasma tungsten wall interaction. This project is dedicated to the experimental research on impurity sputtering and control as well as fuel recycling at target plane of the W divertor, by virtue of the spectroscopic and infrared systems for divertor wall diagnostics developed on our own and other EAST physics diagnostics including divertor probe system. By combining experimental results with code simulation, the boundary particle behaviors at target plane and their influences on long pulse discharge will be deeply understood and evaluated under different environments, which will promote the optimization of divertor configuration and the development of advanced particle control methods. These will eventually contribute, in the aspect of plasma wall interaction, to exploration of high performance long pulse operation scenarios compatible with tungsten divertor and provide valuable experiences for ITER and CFETR.

钨用于聚变装置壁材料面对的一个重要问题是其与等离子体相容性较差，此外，较低的燃料滞留率使钨壁具有不同于碳壁的边界燃料再循环行为，可能影响高约束等离子体中边界局域模的特征。EAST在世界上率先将类似ITER的钨铜monoblock穿管部件用于承受最高热负荷的偏滤器靶板区，如何在全钨偏滤器条件下获得高性能长脉冲等离子体是EAST面临的一个重大挑战，深入认识和有效控制等离子体与钨壁相互作用是关键之一。本项目将依靠自主发展起来的偏滤器光谱、红外等壁诊断系统及其它EAST上相关物理诊断，针对偏滤器靶板的钨瓦块结构开展杂质溅射与控制及燃料再循环的实验研究，结合程序模拟，深入理解不同条件下钨靶板边界粒子行为及其对长脉冲放电的影响，促进钨铜偏滤器位形的优化和先进粒子控制手段的发展，从等离子体与壁相互作用角度，为发展与钨偏滤器相兼容的高性能长脉冲等离子体运行模式提供指导，也将给ITER和CFETR提供借鉴。

钨将被用作国际热核聚变实验堆（ITER）的偏滤器面对等离子体材料，也是下一代聚变堆首选的第一壁材料。但作为高Z杂质，钨在高温等离子体中具有较高的辐射效率，会严重降低等离子体性能，甚至使放电无法持续。此外，到达偏滤器的强烈粒子流和热流对钨材料的溅射也会影响面对等离子体材料部件的寿命。EAST在2014年将上偏滤器升级成类似ITER的全钨偏滤器。本项目发展了偏滤器多道可见光谱诊断，系统地研究了EAST钨偏滤器的杂质溅射和燃料再循环行为，获得其基本特征，结合计算模拟揭示其主要机理，理解不同加热源引起钨溅射的主要机制；深入认识壁涂层、杂质注入、超声分子束（SMBI）充气、共振磁扰动（RMP）、低杂波（LHW）等抑制钨溅射方法的基本过程和存在的问题，发现LHW和RMP引起的三维场效应会导致偏滤器钨杂质源的分裂，可能影响偏滤器钨杂质的屏蔽效果；研究了影响钨靶板燃料再循环行为的主要因素，获得这种再循环对等离子体L-H模转换和边界局域模（ELM）频率的影响规律。这些成果为EAST发展偏滤器脱靶反馈控制，降低偏滤器电子温度，抑制偏滤器靶板钨溅射，控制芯部钨杂质浓度提供了重要的支持，也可以为ITER和中国聚变工程实验堆（CFETR）提供参考。