Year: 2026
Type: article
Abstract: The turbulent transport of toroidal angular momentum helps determine the rotation profiles of tokamak plasmas, and thereby their confinement and stability. The electron contribution therein has an additional consequence: even a modest electron momentum flux can correspond to a substantial turbulent flux of toroidal current, whose divergence could in principle modify the safety-factor profile. Here, using nonlinear gyrokinetic simulations, we show that electromagnetic fluctuations qualitatively alter turbulent momentum transport. In microtearing-mode-driven turbulence, the total momentum transport is inefficient relative to that of heat, yet an electron contribution associated with the turbulent Maxwell stress dominates the momentum flux. We show that this contribution exceeds an estimated scale required for turbulent current redistribution to compete with the collisional processes maintaining the bootstrap current. In the case of kinetic-ballooning-mode-driven turbulence considered, the momentum transport is found to be stronger and remains dominated by the electrostatic ion contribution; nevertheless, retaining the Maxwell stress is essential for the electron momentum flux to exceed this bootstrap-based reference scale. To enable this study, we independently implemented complete electromagnetic momentum-flux diagnostics in the gyrokinetic codes GENE and CGYRO, and verified them through linear and nonlinear cross-code benchmarks. Taken together, these results suggest that electromagnetic momentum transport may potentially be important for the coupled evolution of the rotation, current, and safety-factor profiles in high-beta tokamak plasmas.
Source: Nuclear Fusion
Authors: Haomin Sun, Toby Adkins, Justin Ball, Yann Camenen
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $2,595
Funders: U.S. Department of Energy, EUROfusion, European Commission, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Centro Svizzero di Calcolo Scientifico, National Supercomputing Centre Singapore, nccr – on the move, Euratom Research and Training Programme, Engineering and Physical Sciences Research Council, Staatssekretariat für Bildung, Forschung und Innovation, Laboratory Directed Research and Development
Awards: G115085052, G157624241, Implementation of activities described in the Roadmap to Fusion during Horizon Europe through a joint programme of the members of the EUROfusion consortium, G2293481551, G3562821882, G4738563536, G4896746546, G5566182124, UKAEA / EPSRC Fusion Grant 2022/27, G6354847870, G663282964
OpenAlex ID: W7172495637