The study and prediction of velocities in the pedestal region of Alcator C-Mod are important for understanding plasma confinement and transport. In this study we examine the simplified neoclassical predictions for impurity flows using equations developed for plasmas with background ions in the Pfirsch–Schlüter (PS) (high collisionality) and banana (low collisionality) regimes. B5+ flow profiles for H-mode plasmas are acquired using the charge-exchange recombination spectroscopy diagnostic on Alcator C-Mod and are compared with calculated profiles for the region just inside the last closed flux surface. Reasonable agreement is found between the predictions from the PS regime formalism and the measured poloidal velocities for the steep gradient region of the H-mode pedestals, regardless of the collisionality of the plasma. The agreement is poorer between the neoclassical predictions and measured velocity profiles using the banana regime formalism. Additionally, comparisons of measured velocities from the low- and high-field sides (LFS and HFS) of the plasma lead us to infer the strong possibility of a poloidal asymmetry in the B5+ density. This asymmetry can be a factor of 2–3 for the region of the steepest gradients, with the density at the HFS being larger. The magnitude of the density asymmetry is found to be correlated with the magnitude of the poloidal velocity at the LFS of the plasma.
Alcator C-Mod台基区速度的预测与研究对于理解等离子体约束和输运具有重要意义。在本研究中，我们利用适用于背景离子处于Pfirsch–Schlüter（PS）区（高碰撞率）和香蕉区（低碰撞率）的等离子体方程，检验了杂质速度的简化预测。通过Alcator C-Mod上的电荷交换复合光谱诊断获得了H模台基区的B5+速度分布，并将其与最内闭合磁面以内区域的计算分布进行了比较。结果表明，在台基陡峭梯度区，无论等离子体碰撞率如何，PS区形式论的预测与实测极向速度均吻合良好。而采用香蕉区形式论的预测与实测速度分布的吻合度较差。此外，对等离子体低场侧（LFS）和高场侧（HFS）实测速度的比较表明，B5+密度很可能存在极向不对称性。在梯度最陡区域，该不对称性可达2–3倍，其中高场侧密度更大。研究发现，密度不对称性的幅度与等离子体低场侧极向速度的幅度相关。