Dynamics of pellet ablation clouds observed in LHD by a fast-framing tangentially viewing soft X-ray camera
Dynamics of pellet ablation clouds observed in LHD by a fast-framing tangentially viewing soft X-ray camera
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通过快速成帧切向观察软 X 射线相机在 LHD 中观察到的颗粒烧蚀云动态
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发表时间：
1990
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通讯作者：
S. Yamamoto
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作者：
S. Ohdachi;K. Toi;R. Sakamoto;H. Yamada;G. Fuchs;S. Yamamoto
氢冰球注入是一种很有前途的大规模磁约束等离子体燃料。在目前的反应堆相关实验场景中，例如ITER，需要电子密度接近格林沃尔德极限的操作。需要进一步了解颗粒-等离子体相互作用以提高堆芯燃料效率；为此，人们对烧蚀云的运动进行了广泛的研究。例如，为了提高换料效率，在ASDEX升级[1]中尝试了从托卡马克高场侧进行注入。由于烧蚀材料向低磁场侧漂移，颗粒沉积在等离子体中更深，从而显着提高了燃料效率。与径向位移相比，沿磁力线的烧蚀云的扩张并没有引起那么多的关注。在大螺旋装置（LHD）中，颗粒注入已经成功地用于加注以及[3]。通过连续注射微球——通常是五个连续注射——我们可以达到电子密度超过1×10m的操作状态。虽然颗粒确实穿透得更深，但密度增加仅限于边缘区域附近。最近，在LHD[4]上进行了从船内侧（平均高场侧）和螺旋线圈侧（局部高场侧）的注入。结果表明，密度向外再分布减少，但烧蚀材料的动力学不能完全理解。在这里，我们报告了通过软x射线（SX）测量看到的从颗粒中烧蚀的物质的运动，该测量确实具有良好的空间和时间分辨率。除了标准的SX阵列测量外，还使用了切向观察SX相机[5]（参见图1）。这种相机是基于针孔相机设计的。它利用荧光粉板将SX图像（通过切向观看端口看到）转换成可见图像，并用快速分幅摄像机记录下来。帧率分别为4.5kHz（全帧）和13.5kHz（减帧宽度）。这个速度足以研究瞬态颗粒诱导密度不对称的空间结构。
Hydrogen ice pellet injection is a very promising candidate to fuel large-scale magnetically confined plasmas. In the present scenario of reactor relevant experiments, e.g. ITER, operations with an electron density close to the Greenwald limit are required. Further understanding of pellet–plasma interaction towards improvement of the core fuelling efficiency is needed; to this end the motion of ablated clouds has been extensively studied. E.g., in order to increase the refuelling efficiency, injections from the high field side of the tokamak have been tried in ASDEX upgrade [1]. Due to the drift of the ablated material toward the low magnetic field side, the pellets get deposited deeper into the plasma, thereby significantly improving the fuelling efficiency. In contrast to radial displacements, expansion of ablation clouds along magnetic field lines has not attracted so much attention[2]. In the Large Helical Device(LHD) pellet injection has been successfully used for fuelling as well [3]. By sequential injection of pellets – typically five in sequence – we can reach an operational regime with an electron density in excess of 1×10m. Although the pellets do penetrate deeper, the density increase is localized near the edge region. Recently injections from the inboard side (averaged high field side) and from the helical coil side (local high field side) have been carried out on LHD [4]. It turned out, that the outward density re– distribution is thereby reduced, however, the dynamics of the ablated materials could not fully be understood. Here, we report on movements of the material ablated from the pellet seen by soft Xray (SX) measurements that do have good space and time resolution. In addition to the standard SX array measurements, a tangentially viewing SX camera[5] has been used (cf., Fig, 1). This camera is based on a pinhole camera. It converts SX images – seen through a tangentially viewing port – into visible ones by use of a phosphor plate and records them with a fast framing video camera. The framing rates are respectively 4.5kHz (full frame) and 13.5kHz (reduced frame width). This speed is sufficient to investigate the structure in space of transient pellet–induced density asymmetries.