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arXiv · 2609.31424

Impact of magnetic drift configuration on the edge radial electric field in the TCV tokamak

S. Rienäcker·L. Vermare·P. Hennequin·C. Honoré·B. Labit·S. Coda·L. Frassinetti·B. Vincent·O. Panico·Y. Wang·K. Singh
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Abstract

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.

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S. Rienäcker, L. Vermare, P. Hennequin, C. Honoré, B. Labit, S. Coda, L. Frassinetti, B. Vincent, O. Panico, Y. Wang, K. Singh. 2026-09-25. Impact of magnetic drift configuration on the edge radial electric field in the TCV tokamak. https://arxiv.org/abs/2609.31424

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