托卡马克第一壁H/D滞留及再循环激光诱导击穿光谱原位诊断研究

During tokamak discharge operation, the fuel retention (hydrogen isotope H/D) will be arisen on the first wall because of the plasma wall interaction (PWI). The fuel retention has become a key issue due to that the retention will affect the particles recycling, reduce the efficiency of plasma heating, destroy the plasma confinement and lead to potential risk. In this framework, in-situ and real-time diagnosis of H/D retention and recycling is very significant for understanding of mechanism of fuel retention, to optimize wall conditioning and to improve plasma performance. In this project, a laser-induced breakdown spectroscopy (LIBS) technique, which has been developed by our team with cooperation with EAST team, will be real-time used to investigate H/D retention on the first wall of EAST in the variant wall conditioning, wall cleaning and discharging parameters. The dynamic evolution of H/D retention processes on several tile materials will be characterized during long-pulse discharge operation of EAST. The influence relationship between the H/D retention and plasma performance will be investigated. A deepening understanding about mechanism of the retention and recycling processes could be obtained. The results would provide the direct reference data and improve first wall diagnosis in advanced tokamak devices.

托卡马克装置放电过程中，等离子体与第一壁相互作用（PWI）将导致壁表面发生燃料（氢同位素H/D）滞留，并影响长脉冲托卡马克的粒子再循环和等离子体加热性能，破坏等离子体约束，导致严重安全隐患，成为当前亟待研究的关键问题之一。因此实时原位研究托卡马克第一壁的H/D滞留及再循环过程，对理解燃料滞留机制、优化壁处理方法、提升等离子体参数等具有重要意义。本项目拟依托与中科院等离子体所合作建立的EAST激光诱导击穿光谱（LIBS）壁原位诊断系统，开展H/D滞留原位测量工作，实时分析第一壁表面H/D滞留特性，探索壁处理、壁清洗、放电等不同实验条件对滞留规律的影响。结合不同加料过程细致研究EAST长脉冲运行中壁H/D 滞留动态演化过程，揭示第一壁燃料滞留对再循环和等离子体性能的影响。本项目的研究结果将深化对长脉冲托卡马克燃料滞留及再循环过程的理解，为先进托卡马克（ITER）壁诊断提供参考数据和实验支撑。

等离子体与壁材料相互作用中的燃料滞留问题是制约磁约束核聚变发展的重要因素之一，本项目通过EAST托卡马克的原位LIBS系统，开展EAST第一壁燃料滞留元素原位诊断实验，进一步研究对长脉冲托卡马克燃料滞留及再循环过程。项目期内发表标注SCI论文16篇、授权专利3项、申请专利2项，本人在首届中国磁约束聚变能大会上做邀请报告1次、做国际会议口头报告4次。主要研究成果如下：通过对EAST原位LIBS系统升级，满足在EAST托卡马克放电间隔开展第一壁燃料元素和杂质元素的实时分析测量需要，在有锂化壁处理条件和D放电的情况下，D燃料滞留深度约为几百nm，D/(D+H)滞留比例约为60%，显著低于芯部等离子体中的D比例；在EAST长脉冲高约束运行模式下，利用LIBS系统结合边界OES光谱获得该边界D粒子通量和剂量，将每炮离子通量和剂量与该炮之后的壁表面滞留比例建立关联，发现高场第一壁的D滞留量与边界D等离子体剂量呈正相关、而与边界D等离子体的通量关联度低；在锂化过程中高场侧第一壁Li沉积层厚度逐渐增加，测定了45 g Li在高场中平面处的沉积厚度为1.3 μm，平均沉积率为0.52 μm/h。每天的Li沉积层厚度增加量与当天的锂化用量呈正相关；在离子回旋清洗过程中，发现在EAST高场侧中平面处第一壁W中的D滞留比例低于Mo的滞留比例。对EAST下偏滤器石墨瓦的离线LIBS分析结果表明各杂质主要分布在共沉积层中，沉积层厚度在~10 μm量级。W7-X仿星器限制器石墨瓦和偏滤器螺栓表面H滞留量分别为~10^22 m^-2和~10^21 m^-2。实验室的CF-LIBS定量分析结果对部分W/Cu元素的测量精度误差在20%以内，可实现LIBS结果的半定量化。相关研究技术已应用于EAST上偏滤器原位LIBS诊断系统研制、德国W7-X仿星器偏滤器原位LIBS系统研制和HL-2M托卡马克原位LIBS系统设计研发中，并为LIBS技术应用于未来大型托卡马克装置（ITER、CFETR等）PWI诊断提供直接相关数据和实验支撑。