基于小波变换的Stark展宽算法的优化研究

为了提升Stark展宽计算等离子体电子密度的准确性,基于小波阈值去噪处理方法,对EAST氘原子光谱信号进行了处理,以信噪比(SNR)和均方根误差(RMSE)作为滤波效果的评价依据,通过对比确定了最优小波基db4,最优小波分解4层。根据噪声估计值计算适合的阈值参数进行信号重构,并将经过去噪处理后的数据应用到后期Stark展宽算法计算等离子体密度的分析过程中。结果表明,小波硬阈值去噪能够有效提高光谱信号信噪比、降低均方根误差,在消除光谱信号中噪声的同时,最大程度保留了有用的光谱细节特征信息,进而有利于光谱数据的建模效果,获得更为准确的等离子体电子密度。     

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。     

Experimental investigation on divertor tungsten sputtering with neon seeding in ELMy H-mode plasma in EAST tokamak

Neon (Ne) seeding is used to cool the edge plasma by radiation to protect the divertor tungsten (W) target in the Experimental Advanced Superconducting Tokamak (EAST). The W sputtering in the outer divertor target with Ne seeding is assessed by the divertor visible spectroscopy system. It is observed that the W sputtering flux initially increases with Ne concentration in the divertor despite the decreasing plasma temperature. After reaching a maximum around 25 eV, the W sputtering rate starts to decrease, presenting a suppression effect. The effect on the divertor W sputtering flux and yield due to the competition between the increase of the Ne concentration and the decrease of the plasma temperature is discussed. The results show that enough Ne seeding is essential to effectively reduce the electron temperature and thus to suppress W sputtering. Moreover, ELM suppression is observed when Ne and W impurities enter the core plasma, which could be correlated to the enhanced turbulence transport in the pedestal.