Particle Transport Study by Imaging Diagnostics with Tracer-Encapsulated Pellet

用示踪剂包裹固体颗粒(TESPEL)注入到美国国家核聚变科学研究所(NIFS)的大型螺旋装置(LHD)等离子体中，通过各种诊断方法观察到了示踪杂质离子的行为，并获得了良好的准确性。在高能(150~180keV)中性束(Nb)的电荷交换复合谱(CXRS)中，示踪离子与中性粒子的电荷交换截面通常很小。然而，在真空-紫外线(VUV)和超软X射线领域中的高能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，在铲运机上安装了一台低能量(40keV)Nb注入器。这种低能Nb与我们的研究成果相结合，可能会为高空间分辨率的示踪离子行为的测量开辟道路。用通常的真空紫外光谱和X射线光谱，观察到示踪离子在等离子体中的行为，其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AXUV光电二极管阵列信号的二维层析成像，从二维上观察了示踪离子的行为。AXUVD光电二极管阵列配以合适的滤光片将是一种有效的成像诊断方法。为了从TESPEL注入的实验数据中获得高精度的输运系数，开发了一个针对星体等离子体的杂质输运优化程序。基于我们的研究结果，TESPEL注入杂质输运的全尺度成像诊断即将准备就绪。

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.