HL-2A/M壁表面杂质及燃料滞留皮秒激光诱导击穿光谱定量诊断研究

During tokamak discharge operation, the fuel retention and impurity deposition will be arisen on the first wall due to the Plasma Wall Interaction (PWI). This has become a key issue because the fuel retention and impurity transport will destroy the plasma confinement and lead to potential risk. Laser-Induced Breakdown Spectroscopy (LIBS) has been considered as the most potential diagnostic to in situ obtain safety-relevant nuclear inventory data in between and during plasma discharges. Currently, the nanosecond Laser-Induced Breakdown Spectroscopy (ns-LIBS) has been utilized to diagnose the first wall semi-quantitatively with the depth-resolution of ns-LIBS in the order of 1 μm and the mass removal per pulse in the order of 10 μg. In this project, a picosecond laser-induced breakdown spectroscopic diagnostic approach (ps-LIBS) is proposed and will be developed to improve significantly the diagnostic ability compare with the ns-LIBS. The experimental parameters, include laser wavelength, laser fluence and laser incidence angle will be investigated to achieve the measurement with depth-resolution of 10-100 nm and ablation mass removal less than 50 ng per pulse. Moreover, the spatial-temporal dynamics of ps-LIBS and picosecond laser produced plasma will be investigated to obtain the high ratio signal to noise ps-LIB spectra for the purpose of quantitative analysis. The adverse effects from laser energy jitter, change of surface reflectance and matrix effect will be calibrated to further improve the precision and accuracy on the quantitative ps-LIBS analysis. As the results, the surface composition on the plasma facing components (PFCs) of HL-2A/M tokamak will be diagnosed quantitatively in the depth-resolution of 10-100 nm and ablation mass removal less than 50 ng per pulse. These results can provide directly the detail information of the surface composition on the PFCs of HL-2A/M. The ps-LIBS approach significantly upgrades the current PWI-diagnostics and improve the understanding of the PWI processes as well as help one to design a powerful PWI diagnostic approach to monitor the fuel retention and impurity deposition on PFCs of the future tokamak devices, like ITER and CFETR.

托卡马克运行中，等离子体与壁相互作用（PWI）会导致壁表面发生燃料滞留、杂质沉积，破坏等离子体约束，引发严重安全隐患，是当前亟待研究的关键问题之一。激光诱导击穿光谱（LIBS）被公认为是最具潜力可在线诊断壁表面杂质和燃料滞留的方法。本项目提出皮秒LIBS（ps-LIBS）方法以克服常规纳秒LIBS（ns-LIBS）方法壁损伤大（10 μg/脉冲）、深度分辨率低（μm量级/脉冲）、定量精准度差（半定量）等缺点，通过优化ps-LIBS实验参数和研究其光谱时空动力学演化特性，进一步地校正由激光能量抖动、靶材表面反射率变化、基体效应对定量分析的影响，获得高信噪比优化光谱信号，在近无损伤（小于50 ng/脉冲）、高深度分辨（10-100 nm）条件下实现壁表面杂质与燃料滞留的定量诊断分析。本项目的顺利实施将极大地提升现有壁诊断研究的能力，为深入理解托卡马克PWI物理过程提供重要的实验支撑。

托卡马克运行中，等离子体与壁相互作用（PWI）会导致壁表面发生燃料滞留、杂质沉积，破坏等离子体约束，引发严重安全隐患，是当前亟待研究的关键问题之一。激光诱导击穿光谱（LIBS）被认为是最具潜力可在线诊断壁表面元素的方法。本项目建立了超短脉冲皮秒激光诱导击穿光谱诊断系统（ps-LIBS）以克服常规纳秒LIBS（ns-LIBS）技术壁损伤大（10 μg/脉冲）、深度分辨率低（μm量级/脉冲）、定量精准度差（半定量）等缺点。通过对皮秒激光与物质相互作用的研究，优化了ps-LIBS诸多实验参数和其光谱时空动力学演化特性，并对HL-2A/M拟使用的钨进行了研究，国际上首次在近无损伤（~50 ng/脉冲）、高深度分辨（~40 nm）条件下实现钨壁的高分辨率诊断，同时给出了一种在不改变深度分辨率条件下优化ps-LIBS信号的方法。进一步地提出了一种适用于等离子体面壁部件（PFCs）腐蚀与沉积诊断的ps-LIBS定量分析方法，并建立模型校正由激光光斑引起的定量误差，提升了ps-LIBS定量的能力。同时项目负责人与德国的W7-X合作，采用这一方法定量描绘出了PFCs的刻蚀与沉积图样，ps-LIBS结果与原位红外热成像仪热导结果图样符合。项目执行期间，发表标注SCI论文6篇（第一/通讯作者5篇、合著1篇），受理专利4项（授权1项），在国内外会议上做口头邀请报告3次，获得LIBS领域重要学术会议“第八届全国LIBS会议优秀青年科学家报告奖”，对提升我国PWI研究领域的国际地位具有积极意义。同时项目的研究成果，一方面极大地提升现有LIBS技术的诊断能力；另一方面也为LIBS技术高分辨定量诊断PFCs，并进一步深入理解PWI物理过程提供重要技术手段与数据支撑。