Edge plasma control with a Local Island Divertor

本研究项目的目的是开展局部岛偏滤器（LED）的技术和设计研究，并将其应用于聚变实验装置，特别是大螺旋装置（LHD）中。LID是一种使用在边缘区域形成的m/n=1/1岛的偏滤器。穿过岛分界线的向外的热和粒子通量沿着场线流到岛的背面，在那里偏滤器板被放置在偏滤器头上以接收热和粒子负载。在那里回收的颗粒由泵送系统泵出。与传统的泵限制器不同，偏滤器头部的前缘位于标准LID配置的岛内部，从而受到保护，免受来自堆芯的向外热通量的影响。LID的原理已经在紧凑螺旋系统（CHS）的实验研究中得到了验证。在本研究项目中，首先利用CHS的实验测量结果和理论预测（例如，通过MonteCarlo中性粒子模拟程序）进行了理论和观测之间的比较。这为我们提供了关于Heliotron型设备中边缘等离子体行为的关键信息，并帮助我们优化LHD LID的设计。完成了偏滤器头部和抽气通道的几何设计，实现了一种具有30%以上抽气效率的闭式偏滤器结构。高效率的抽运是实现高温偏滤器运行的关键，在高温偏滤器中产生几keV的偏滤器等离子体，导致显著的能量约束改善。在完成技术研究之后，LID被制造出来，并于2002财政年度末安装在LHD上。2003年进行的初步实验表明，LID具有预期的基本偏滤器功能，因此，本研究项目的目标得以实现。

Aims of this research project are to develop technical and design studies of a local island divertor (LED) and to realize it in fusion-experiment devices, especially in the Large Helical Device (LHD).The LID is a divertor that uses an m/n=1/1 island formed at the edge region. The outward heat and particle fluxes crossing the island separatrix flow along the field lines to the back of the island, where divertor plates are placed on a divertor head to receive heat and particle loads. The particles recycled there are pumped out by a pumping system. Unlike conventional pump limiters, leading edges of the divertor head are located well inside the island for the standard LID configuration, thereby being protected from the outward heat flux from the core. The principle of the LID has been proved by the experimental study on the Compact Helical System (CHS).In this research project, a comparison between theory and observation was performed at first, using the experimental results measured in CHS and theoretical predictions obtained, for example, by a Monte Carlo neutral-particle simulation code. This provided us critical information on the edge plasma behavior in the heliotron-type device, and helped us to optimize the design of the LID for LHD. Especially, the geometrical design of the divertor head and pumping duct was completed, and a closed divertor configuration was demonstrated to be realized with high pumping efficiency of > 30%. Highly efficient pumping is the key to realizing the high temperature divertor operation, where a divertor plasma with a temperature of a few keV is produced, leading to a significant energy confinement improvement.After the technical studies were finished, the LID was fabricated, and installed in LHD at the end of 2002 fiscal year. Preliminary experiments performed in 2003 suggested the existence of fundamental divertor functions expected for the LID, so that the aims of this research project were achieved.