非轴对称等离子体中的杂质：输运及其对自举电流的影响
Impurities in a non-axisymmetric plasma: transport and effect on bootstrap current
摘要：
杂质引起辐射损失和等离子体稀释，在仿星器等离子体中，新经典双极径向电场通常不利于避免强杂质峰。在这项工作中，我们使用了一个新的连续漂移动力学求解器，SFINCS代码（Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver）[M。Landreman等人，Plasmas 21（2014）042503]，其采用完全线性化的Fokker-Planck-Landau算子来计算Wendelstein 7-X（W7-X）磁配置的新经典杂质输运系数。我们比较SFINCS计算与理论渐近线在高碰撞极限。我们观察并解释了1/nu标度的物种间的径向输运系数在低碰撞性，由于在物种间的碰撞运营商，这是没有发现与简化的碰撞模型，即使当动量修正。然而，如果存在径向电场，则这种类型的缩放消失。我们还利用SFINCS分析了杂质含量对新经典杂质动力学和自举电流的影响。我们表明，为了统一的等离子体有效电荷Zeff的变化可以影响自举电流足以导致偏滤器撞击点位置的偏差。
英文摘要：
Impurities cause radiation losses and plasma dilution, and in stellarator plasmas the neoclassical ambipolar radial electric field is often unfavorable for avoiding strong impurity peaking. In this work we use a new continuum drift-kinetic solver, the SFINCS code (the Stellarator Fokker-Planck Iterative Neoclassical Conservative Solver) [M. Landreman et al., Phys. Plasmas 21 (2014) 042503] which employs the full linearized Fokker-Planck-Landau operator, to calculate neoclassical impurity transport coefficients for a Wendelstein 7-X (W7-X) magnetic configuration. We compare SFINCS calculations with theoretical asymptotes in the high collisionality limit. We observe and explain a 1/nu-scaling of the inter-species radial transport coefficient at low collisionality, arising due to the field term in the inter-species collision operator, and which is not found with simplified collision models even when momentum correction is applied. However, this type of scaling disappears if a radial electric field is present. We also use SFINCS to analyze how the impurity content affects the neoclassical impurity dynamics and the bootstrap current. We show that a change in plasma effective charge Zeff of order unity can affect the bootstrap current enough to cause a deviation in the divertor strike point locations.
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