Pedestal structure in H-mode plasmas
Pedestal structure in H-mode plasmas
复制标题
DOI：
10.1088/0029-5515/54/11/116001
复制
发表时间：
2014-11
期刊：
影响因子：
3.3
通讯作者：
Hajime Urano
中科院分区：
文献类型：
--
作者：
Hajime Urano
综述了目前对边座结构的认识。基座等离子体强烈影响聚变功率和分流器热负荷，因此，基座结构的表征取得了重大进展。在高约束模式（h模）等离子体中，基座组件在通过剖面刚度确定核心热输运时起边界条件的作用。另一方面，较高的全局极向β或沙弗拉诺夫位移提高了等离子体边缘在低磁场侧的稳定性，特别是在高三角形处。环面旋转也影响边缘稳定边界。虽然环面流稳定了高n的气胀模式，但它破坏了低n的扭结/剥离模式。在此背景下，从宽度、梯度和高度的几何角度对基座压力剖面进行了表征。虽然压力梯度主要由剥离-气球稳定性极限给出，但许多实验结果表明，基座宽度的尺度近似为基座极坐标β的平方根。观察到一些支持性的实验结果，其中动能气球模式（KBM）被视为存在于基座区域的湍流输运，并解释了基座宽度的经验标度。基于边缘磁流体动力学（MHD）在压力梯度上的稳定性和表征基板宽度的KBM输运，建立了基板高度的预测模型（EPED1），从而可以估计基板高度。根据在ITER中安装全铍第一壁和全钨导流器的决定，对金属壁对基座和约束的影响进行了深入研究。现有金属壁托卡马克的一个共同模式是，基座和整体限制受到增加气体加注（以筛选高z杂质流入）的要求的影响，以及由于基座区域低z杂质浓度的减少而导致基座特性的变化。通过注入低z外部杂质，可以提高基座压力或温度，从而提高能量限制。
The present understanding of edge pedestal structure is reviewed. Pedestal plasma strongly affects fusion power and divertor heat load, and as such, characterization of the pedestal structure has significantly progressed. In high-confinement mode (H-mode) plasmas, the pedestal component plays the role of a boundary condition in determining the core heat transport through profile stiffness. On the other hand, a higher global poloidal beta or Shafranov shift improves the stability of the plasma edge in the low magnetic field side particularly at high triangularity. Toroidal rotation also influences the edge stability boundary. While toroidal flow stabilizes high-n ballooning modes, it destabilizes low-n kink/peeling modes. On the basis of this background, characterization of the pedestal pressure profile has been attempted from a geometrical viewpoint of width, gradient and height. While the pressure gradient is given mainly by the peeling–ballooning stability limit, many experimental results indicate the pedestal width scales approximately as the square root of the poloidal beta at the pedestal. Some supportive experimental results were observed where the kinetic ballooning mode (KBM) was seen as a turbulent transport that exists in the pedestal region and explained the empirical scaling of the pedestal width. A predictive model of the pedestal height (EPED1) has been developed, in which the pedestal height can be consequently estimated by knowledge of the edge magneto-hydrodynamic (MHD) stability on the pressure gradient and the KBM transport characterizing the pedestal width. The influence of the metal wall on the pedestal and confinement has intensively been studied in accordance with the decision of the installation of a full beryllium first wall and a full tungsten divertor in ITER. A common pattern among the existing metal wall tokamaks has been found that the pedestal and global confinement are affected by a requirement for increased gas fuelling (to screen high-Z impurity influxes) as well as a change in pedestal characteristics due to a decrease of the low-Z impurity concentration in the pedestal region. The pedestal pressure or temperature, and thus the energy confinement, can be raised by seeding low-Z extrinsic impurities.