Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport
Flux-surface variations of the electrostatic potential in stellarators: impact on the radial electric field and neoclassical impurity transport
复制标题
仿星器静电势的通量表面变化：对径向电场和新古典杂质输运的影响
DOI：
10.1088/1361-6587/aac700
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发表时间：
2018
影响因子：
2.2
通讯作者：
M. Nunami
中科院分区：
文献类型：
--
作者：
A. Mollén;M. Landreman;H. Smith;J. M. García;M. Nunami
在标准新古典理论中，静电势的通量面变化通常被忽略，但在3D器件中，它们可以大到足以影响杂质的径向粒子通量。径向局部漂移动力学方程求解器SFINCS（仿星器福克-普朗克迭代新古典保守求解器）（Landreman et al 2014 Phys. Plasmas 21 042503）已经更新，以考虑这些变化。在目前的工作中，我们使用SFINCS进行新古典粒子输运的仿星器，在那里我们同时占通量表面势的变化，几个动力学物种，包括非绝热电子和非痕量杂质，和完全线性化的Fokker-Planck-朗道碰撞算子的自我和物种间的碰撞（没有扩大的质量比）的一种新的研究。我们还对双极径向电场进行了自洽计算，分析了磁通面变化和非痕量杂质的存在对双极径向电场的影响。在一个模拟的温德尔斯坦7-X等离子体中，我们发现通量表面的变化对所有等离子体物种的径向粒子通量的影响很小。相比之下，对于实验中的大螺旋装置（LHD）的杂质空穴放电的碳通量可以强烈修改的磁通表面电位的变化，也可以改变计算的双极径向电场。然而，在中间半径附近的电位变化导致增强向内的新古典碳通量，而不是导致向外的通量，从而表明通量表面电位变化在新古典输运中的作用可能不是LHD等离子体中观察到的杂质空穴现象的解释。
Flux-surface variations of the electrostatic potential are typically neglected in standard neoclassical theory, but in 3D devices they can be large enough to affect the radial particle flux of impurities. The radially local drift-kinetic equation solver SFINCS (stellarator Fokker–Planck iterative neoclassical conservative solver) (Landreman et al 2014 Phys. Plasmas 21 042503) has been updated to account for these variations. In the present work we use SFINCS to perform a novel study of neoclassical particle transport in stellarators, where we simultaneously account for the flux-surface potential variations, several kinetic species including non-adiabatic electrons and non-trace impurities, and the full linearized Fokker–Planck–Landau collision operator for self- and inter-species collisions (with no expansion made in mass ratio). We also make a self-consistent calculation of the ambipolar radial electric field, to analyze how it is affected by the flux-surface variations and the presence of non-trace impurities. In a simulated Wendelstein 7-X plasma, we find that the impact of the flux-surface variations on the radial particle fluxes of all plasma species is small. In contrast, for an experimental impurity hole discharge in the Large Helical Device (LHD) the carbon flux can be strongly modified by the flux-surface potential variation and also the calculated ambipolar radial electric field can change. However, around mid radius the potential variations cause enhanced inward neoclassical carbon fluxes, rather than causing outward fluxes, thus suggesting that the role of flux-surface potential variations in neoclassical transport may not be the explanation for the impurity hole phenomenon observed in LHD plasmas.