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First-Principles Explanation of the Drift Configuration Dependence of the Radial Electric Field and High-Confinement
B J Frei1, R Bilato1, O Grover1
1Max-Planck Institute for Plasma Physics, Boltzmannstraße 2, Garching, D-85748, Germany.
Abstract:
The origin of the difference in the high-confinement (H-mode) power threshold between favorable and unfavorable drift configurations in tokamaks-experimentally linked to a deeper radial electric field (E_{r}) well in the former-remains unresolved. Using first-principles gyrokinetic simulations of edge and scrape-off-layer turbulence in the ASDEX Upgrade tokamak, we show that turbulence-driven poloidal flows generate this deeper E_{r} well in the favorable configuration through enhanced nonlinear turbulence-mean flow energy transfer. This transfer is significantly weaker in the unfavorable case, yielding a shallower E_{r} well, while turbulence intensity is simultaneously higher. Within the turbulence-flow shear suppression paradigm, the combination of stronger shear and reduced turbulence facilitates H-mode access in the favorable configuration. These results provide the first validated, self-consistent full-f gyrokinetic explanation of how drift configuration controls the nonlinear dynamics of profiles, E_{r}, flows, and turbulence, thereby setting the H-mode power threshold.
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