Relationship between fuelling profile and structure and structure formation in boundary region of fusion plasmas

这项研究的目的是了解聚变等离子体边界区自形成的边缘基座的空间结构(即其宽度和梯度)与燃料分布之间的关系。JT-60U与法国CEA-Cadarache公司合作，在JT-60U上安装了一种新的加油装置燃气喷射器。气体射流可以向等离子体中注入超音速气体，它的加注剖面介于目前JT-60U上使用的充气注入器和弹丸注入器之间。JT-60U真空室烘烤温度过高(~300℃)，如何避免喷油器头部的真空密封损坏是装置的关键问题。通过采用高耐热材料和烘烤过程中较高的进气压力来降低密封应力，并将烘烤温度降低到~80℃，首次在大型托卡马克等离子体中成功地注入了气体射流。背景气压为4~6bar，频率为4~10 Hz时，可观察到密度跳跃。尽管气体喷流的光几乎发射到分界线外，但即使在归一化小半径为~0.8的情况下，也观察到离子温度的快速下降。在这一点上，气体喷射可能会对等离子体参数产生影响。在这个点内，冷脉冲传播到中心区域。由边缘基座结构决定的基座电子压力保持不变，因为温度随着密度的增加而降低。气体射流没有观察到边缘压力的增强，而高场侧球丸注入则观察到了边缘压力的增强。基座离子温度也随着气体喷射的增加而降低。随着气体射流密度的增加，束流密度降低。今后，在更宽的实验范围内研究底座结构对背景气体压力和频率的参数依赖性是很重要的。

The objective of this research is to understand relationship between fuelling profile and spatial structure of edge pedestal (i.e. its width and gradient) which is self-formed in the boundary region of fusion plasmas. A new fuelling device gas-jet has been installed on JT-60U in collaboration with CEA-Cadarache, France. Gas jet can inject supersonic gas into plasmas and it has intermediate fuelling profile between those of gas-puffing and pellet injector which are so far used in JT-60U. It was critical issue for the installation to avoid damage of the vacuum seal placed in the injector head owing to high baking temperature for the JT-60U vacuum vessel (〜300 degree C). By applying high heat resistant material, high feeding gas pressure during the baking to reduce the stresses on the seal and reduction of baking temperature to 〜80 degree C, gas jet was successfully injected in the large tokamak plasma for the first time. Density jumps were observed with the background gas pressure of 4-6 bar and the frequency of 4-10 Hz. Although light from the gas jet was almost emitted outside the separatrix, quick decreases in the ion temperature were observed even at a normalized minor radius of 〜0.8. The gas jet could directory affect the plasma parameters at this point. Inside this point, cold pulse propagated into the central region. The pedestal electron pressure determined by the edge pedestal structure was kept constant, because the temperature was decreased with increasing the density. Enhancement of the edge pressure was not observed with gas-jet, while it was observed with high-field-side pellet injections. The pedestal ion temperature was also decreased with the gas-jet. Confinement degraded when the density was increased with the gas-jet. In future, it is important to investigate parameter dependence of the pedestal structure in the wide experimental ranges for background gas pressure and frequency.