EAST边界和芯部杂质谱线的时间延迟研究

边界杂质注入是未来聚变装置ITER用于增强边界辐射，减少第一壁热负荷的一种重要方法。但部分注入的杂质会被输运到芯部，造成主等离子体辐射损失以及约束下降。光谱观测可以获取杂质种类、含量和分布等信息，在理解等离子体中杂质输运方面起着重要作用。在EAST（experimental advanced superconducting tokamak）偏滤器氩气（Ar）注入实验中，利用偏滤器可见光谱和芯部极紫外光谱监测边界的Ar1+离子谱线Ar Ⅱ(401.36 nm)和芯部的Ar15+离子谱线Ar ⅩⅥ(35.39 nm)，并获得两者强度随时间的变化。其中，Ar Ⅱ和Ar ⅩⅥ的电离能分别为27和918 eV，因此，Ar Ⅱ和Ar ⅩⅥ分别对应分布于等离子体边界和芯部Ar离子。为了分析二者谱线强度随时间变化的特征，发展了一种基于正则Pearson积矩相关系数的相关分析方法，计算得到两者谱线强度变化的相对延迟时间，以此表征杂质从边界向芯部输运的时间。结果显示，偏滤器注入Ar杂质后，芯部Ar ⅩⅥ辐射增长滞后于边界Ar Ⅱ辐射的增长，并且在具有较高的低杂波加热功率的放电中，两者的延迟时间较长，表明较高的低杂波加热功率可以延长杂质从边界向芯部输运的时间。

Study on Time Delay of Impurity Line Emissions Between in the Edge and Core Plasmas in EAST Tokamak

Impurity seeding is considered a promising method to enhance edge plasma radiation and mitigate the head load on the vessel surface in the future tokamak devices like ITER. However, part of the injected impurities would inevitably be transported to the plasma core, causing strong core radiation loss and degrading plasma confinement. Spectral observation is an important means to obtain the information on impurity species, concentration and distribution in tokamak which plays an important role in understanding the impurity transport in plasma. During the EAST (experimental advanced superconducting tokamak) diverter Ar seeding experiments, the diverter visible spectroscopy (Div-W) system and the fast-response extreme-ultraviolet (EUV) spectroscopy system is used to detect the line emission of Ar1+ (Ar Ⅱ at 401.36 nm) in the edge and monitor the line emission of Ar15+ (Ar ⅩⅥ at 35.39 nm）from plasma core, separately. Meanwhile, Ar Ⅱ and Ar ⅩⅥ intensities’ time evolution is obtained. The different ionization energies for Ar Ⅱ (27 eV) and Ar ⅩⅥ (918 eV) indicate that Ar Ⅱ and ArⅩⅥ are mainly distributed at the plasma boundary and the core plasma respectively. A correlation analysis method based on regular Pearson product moment has been developed to derive the time delay between the two line emissions from the edge and the core plasma. The relative delay time of Ar Ⅱ and Ar ⅩⅥ is calculated to characterize the transport time of Ar impurities from the boundary to the core. The results show that the rise of Ar ⅩⅥ line emission lags behind Ar Ⅱ line emission after Ar injection in the diverter. Moreover, the delay time is longer in the discharges with higher lower hybrid wave (LHW) heating power, indicating that higher LHW power can prolong the transport time of impurities from the boundary to the core.