Particle Transport Study by Imaging Diagnostics with Tracer-Encapsulated Pellet

用示踪剂封装固体微球（TESPEL）注入到国家聚变科学研究所（NIFS）大螺旋装置（LHD）等离子体中的示踪剂杂质离子，通过各种诊断方法对其行为进行了高精度观察。使用高能（150~ 180kev）中性束（NB）的电荷交换复合光谱（CXRS），示踪离子与中性粒子之间的电荷交换截面通常很低。然而，在真空紫外（VUV）和超软x射线域中具有高能NB的CXRS使我们能够测量示踪离子的发射。基于这一结果对CXRS系统的进一步改进将使我们能够以更高的精度测量示踪离子的行为。最近，LHD安装了一个低能量（40 keV） NB注入器。这种低能NB与我们研究中获得的知识相结合，可能为高空间分辨率测量示踪离子的行为开辟了道路。利用常规的紫外光谱和x射线光谱，观察到示踪离子在等离子体中的电子密度和电子温度几乎没有变化。这一结果将为进一步改进光谱系统提供重要依据。通过对来自AXUV光电二极管阵列的信号进行二维断层扫描，可以二维地观察到示踪离子的行为。AXUVD光电二极管阵列与适当的光学滤波器将是一个有效的成像诊断。为了从TESPEL注入得到的实验数据中获得精度较高的输运系数，开发了一种优化的仿星等离子体杂质输运代码。根据我们的研究结果，用TESPEL注射进行杂质输运的全面成像诊断将很快准备好。

Behaviors of tracer impurity ions, which are deposited into plasmas of the Large Helical Device (LHD) in National Institute for Fusion Science (NIFS) with a tracer-encapsulated solid pellet (TESPEL) injection, have been observed with a good accuracy by various diagnostics. A charge exchange recombination spectroscopy (CXRS) with a high-energy (150~180 keV) neutral beam (NB) usually suffers from a very low charge-exchange cross section between tracer ions and neutral particles. However, the CXRS with the high-energy NB in a vacuum-ultraviolet (VUV) and ultra soft x-ray domain enables us to measure emissions from the tracer ions. Further improvements on the CXRS system based on this result will allow us to measure the behavior of the tracer ions with a higher accuracy. Recently, a low-energy (40 keV) NB injector has been installed in LHD. A combination of this low-energy NB and knowledge obtained from our research may open the way for the measurement of the behavior of tracer ions with a high spatial resolution. With usual VUV and X-ray spectroscopy, the property of the behavior of the tracer ions in the plasma, which shows almost no change in the electron density and the electron temperature, has been observed. This result will be an important basis for the further improvements on the spectroscopic system. By using 2D tomography of signals from AXUV photodiode arrays, the behavior of the tracer ions has been observed two-dimensionally. The AXUVD photodiode arrays with an appropriate optical filter will be an effective imaging diagnostics. In order to obtain transport coefficients with a good accuracy from experimental data obtained by the TESPEL injection, an impurity transport code optimized for stellarator plasmas has been developed. Based on the results obtained from our research, full-scale imaging diagnostics for the impurity transport with the TESPEL injection will be ready soon.