磁漂移位形对TCV托卡马克边缘径向电场的影响

中文摘要 AI 辅助

在托卡马克à Configuration Variable (TCV)中，比较了匹配的L模放电中离子磁漂移方向相反（有利与不利的$B \! \ imes \! \ abla B$位形）情况下的边缘径向电场($E_r$)。正如先前在WEST和AUG托卡马克上报道的那样，通过多普勒背散射（DBS）测量的$E_r$剖面在有利漂移情形下于分界面内侧呈现一个“井”，而在不利情形下该“井”缺失或不太明显。这一观察在广泛的等离子体条件下成立，特别是在具有几乎相同边缘密度和温度剖面的欧姆放电中也是如此。从DBS推断的密度涨落特性没有显著差异：在欧姆加热下，有利位形中的边缘涨落水平往往更高，而径向相关长度相似。边缘$E_r$差异似乎与碳环向旋转行为无关。降低密度或增加辅助加热功率往往会加剧边缘$E_r$差异。等离子体电流对有利和不利$E_r$剖面影响很小——这与WEST的结果形成对比。通过辅助加热接近L-H转变时，有利位形中的边缘$E_r \ imes B$剪切和压力增长更快，且DBS涨落水平相对于不利情形有所降低。总体而言，我们的结果证实边缘$E_r$对磁漂移位形的敏感性是一个稳健的多机器现象，与约束水平和H模可及性有合理联系。

英文摘要

The edge radial electric ($E_r$) in the Tokamak à Configuration Variable (TCV) is compared in matched L-mode discharges with opposite ion magnetic drift directions (favorable versus unfavorable $B \! \times \! \nabla B$ configurations). As previously reported on the WEST and AUG tokamaks, the $E_r$ profile---measured by Doppler backscattering (DBS)---exhibits a "well" just inside the separatrix in the favorable drift case, which is absent or less pronounced in the unfavorable counterpart. This observation holds over a broad range of plasma conditions, notably also in Ohmic discharges with nearly identical edge density and temperature profiles. Density fluctuation characteristics inferred from DBS are not drastically different: Under Ohmic heating, edge fluctuation levels tend to be higher in the favorable configuration, while radial correlation lengths are similar. The edge $E_r$ difference appears uncorrelated with carbon toroidal rotation behavior. Reducing density, or increasing auxiliary heating power tends to accentuate the edge $E_r$ disparity. Plasma current has little impact on both favorable and unfavorable $E_r$ profiles---in contrast to results from WEST. Approaching the L-H transition via auxiliary heating, edge $E_r \times B$ shear and pressure grow more readily in the favorable configuration, and DBS fluctuation levels are reduced relative to the unfavorable case. Overall, our results confirm that the edge $E_r$ sensitivity to magnetic drift configuration is a robust, multi-machine phenomenon, with a plausible connection to confinement level and H-mode access.

发表机构

• Division of Fusion Plasma Physics, KTH Royal Institute of Technology（等离子体物理系，皇家理工学院）

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