EAST高约束模式放电下金属杂质的行为和控制实验研究

The presence of impurities is inevitable in tokamak plasmas and plays an important role in plasma performance, the behavior of metallic impurity with high Z is a problem of major importance for fusion plasma research due to their severe radiation losses and great dilution of fuel. One basic requirement for present and future fusion devices is to achieve a steady-state operation of the high-performance plasma, which requires that the influx of the metallic impurities into the core plasma should be kept at a minimum level, thus the studies on the behavior and control of metallic impurities have been carried out in many tokamaks with great effort. The fully superconducting tokamak EAST is being able to achieve the steady-state operation of plasma and possesses the discharge configurations similar to ITER, the experiments on EAST have just supplied us with an opportunity to study the behavior of intrinsic and deliberately introduced metallic impurities in a machine with the same configuration of fully superconducting as possessed in ITER. Based on some key diagnostic systems such as soft X-ray emission measurement and EUV spectrometer which are well established on EAST, and combined with special code for simulating impurity transport, detailed experimental studies on the behavior and control of metallic impurities in H-mode discharges will be made in EAST experiments, with an attempt to explore an experimental method to effectively mitigate or control the core accumulation of metallic impurities, which can significantly help to achieve quasi-steady-state operation with high-performance plasma on EAST and steady-state operation on future fusion reactors such as ITER.

杂质不可避免地存在于托卡马克等离子体中，并对等离子体行为有重要影响，金属杂质因其较大的辐射损失和较强的稀释性而倍受关注。维持高参数稳态运行是当今和未来聚变装置如ITER所要实现的目标之一，这要求等离子体中的金属杂质含量非常低，因此国际上很多托卡马克均在深入研究金属杂质的行为和控制方法。EAST全超导托卡马克拥有类似于ITER的放电位形，具备稳态运行的能力，在EAST上开展金属杂质相关的物理研究将对ITER的稳态运行提供直接的参考和帮助。本项目将依托EAST实验平台，基于软X射线、EUV光谱、激光汤姆逊散射等关键诊断系统，结合杂质输运模拟代码，通过实验研究来揭示EAST高约束模式（H模）放电等离子体中的金属杂质行为规律，同时探索一种有效缓解或控制金属杂质聚芯的实验方法，为实现EAST高参数准稳态运行以及未来ITER稳态运行提供有意义的参考。

金属杂质因其较大的辐射损失和较强的稀释性而对托卡马克等离子体行为有重要影响，因此，国际上很多托卡马克均在深入研究金属杂质的行为和控制方法。本项目依托EAST托卡马克实验平台，基于一些关键诊断系统，结合杂质输运模拟程序，通过分析诊断实验数据研究了EAST高约束模式（H模）放电等离子体中的金属杂质行为规律。研究内容主要包括：①完善了项目所依赖的关键诊断系统的性能，包括软X射线能谱、可见和EUV光谱、辐射量热等诊断；②研究了EAST不同H模放电条件下金属杂质的辐射行为；③基于输运模拟程序和诊断数据，对部分金属杂质进行了输运分析和研究；④研究了金属杂质聚芯现象，并开展了金属杂质聚芯抑制的实验研究。研究发现：在EAST实验H模放电期间，在金属壁条件下，上偏滤器材料W杂质、射频波天线Cu、Fe等重金属杂质的不可控容易引起等离子体发生H-L转换，甚至破裂。在NBI中性束注入期间，束粒子的穿透和高能粒子与壁的相互作用，是引起杂质源的主要方式。通过电子回旋波（ECRH）和离子回旋波（ICRH）的在轴加热，可以有效避免金属杂质在等离子体芯部的累积，此外，MHD如锯齿、ELM等的出现也是一种有效的金属杂质排除途径。同时，也观察到边界RMP 扰动场的利用对金属杂质的输运影响。目前，在EAST装置上，通过控制ECRH的沉积位置是有效缓解或控制金属杂质聚芯较为可行且容易实现的实验方案。通过本项目研究工作探索出的这种缓解或控制金属杂质聚芯实验方法，为实现EAST高参数准稳态运行以及未来ITER稳态运行提供了有价值的参考。