First-Principles Explanation of the Drift Configuration Dependence of the Radial Electric Field and High-Confinement Access in Tokamaks
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| Main Authors: | , , , , , , , , |
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| Format: | Preprint |
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2026
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| _version_ | 1866918517654159360 |
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| author | Frei, B. J. Bilato, R. Grover, O. Zholobenko, W. Angioni, C. Bergmann, M. Ulbl, P. Jenko, F. Team, the ASDEX Upgrade |
| author_facet | Frei, B. J. Bilato, R. Grover, O. Zholobenko, W. Angioni, C. Bergmann, M. Ulbl, P. Jenko, F. Team, the ASDEX Upgrade |
| contents | 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 (Er) well in the former, remains unresolved. Using first-principles gyrokinetic simulations of edge and scrape-off-layer turbulence in ASDEX Upgrade, we show that turbulence-driven poloidal flows generate this deeper Er 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 Er 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, Er, flows, and turbulence, thereby setting the H-mode power threshold. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2605_23002 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | First-Principles Explanation of the Drift Configuration Dependence of the Radial Electric Field and High-Confinement Access in Tokamaks Frei, B. J. Bilato, R. Grover, O. Zholobenko, W. Angioni, C. Bergmann, M. Ulbl, P. Jenko, F. Team, the ASDEX Upgrade Plasma Physics 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 (Er) well in the former, remains unresolved. Using first-principles gyrokinetic simulations of edge and scrape-off-layer turbulence in ASDEX Upgrade, we show that turbulence-driven poloidal flows generate this deeper Er 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 Er 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, Er, flows, and turbulence, thereby setting the H-mode power threshold. |
| title | First-Principles Explanation of the Drift Configuration Dependence of the Radial Electric Field and High-Confinement Access in Tokamaks |
| topic | Plasma Physics |
| url | https://arxiv.org/abs/2605.23002 |