Fast-ion effects on E× B staircase organization and the heat-flux response to the ion-temperature gradient
Abstract
Zonal-flow organization can modify the relation between heat flux and temperature gradient, but how fast ions affect this organization and the accompanying transport response remains less well characterized. We use nonlinear, global gyrokinetic simulations based on KSTAR fast-ion-regulated enhancement (FIRE) mode to compare cases with and without fast ions during profile relaxation across five initial main-ion temperature gradients. We observe that fast ions induce larger zonal-flow and shearing-rate amplitudes, together with persistent shear layers. At the reference profile based on the experiment, these shear layers coexist with temperature-gradient corrugations qualitatively consistent with E× B staircases. When fast ions are present, inward and outward ion heat fluxes coexist at different radii, which causes the average heat flux to be smaller than when fast ions are absent. This redistribution of ion heat transport may be relevant to understanding the improved ion confinement observed in FIRE mode. In particular, we note a transition-like response in the presence of fast ions, whereby the heat flux decreases as the ion-temperature gradient increases, in contrast to the conventional Fick's law trend without fast ions. This behavior that deviates from Fick's law suggests that FIRE mode may represent a bifurcation to a distinct transport regime rather than a continuous high-performance extension of L-mode. These findings highlight the importance of the initial temperature gradient and global zonal-flow organization when assessing fast-ion effects on ion heat transport.
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BibTeX
@misc{kim2026fastion,
title = {{Fast-ion effects on $E\times B$ staircase organization and the heat-flux response to the ion-temperature gradient}},
author = {Il-Hwan Kim and Jaemin Seo},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.08180},
eprint = {2610.08180},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.08180},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Fast-ion effects on E× B staircase organization and the heat-flux response to the ion-temperature gradient
AU - Il-Hwan Kim
AU - Jaemin Seo
PY - 2026
DA - 2026/10/06
PB - arXiv
DO - 10.48550/arxiv.2610.08180
UR - https://arxiv.org/abs/2610.08180
AB - Zonal-flow organization can modify the relation between heat flux and temperature gradient, but how fast ions affect this organization and the accompanying transport response remains less well characterized. We use nonlinear, global gyrokinetic simulations based on KSTAR fast-ion-regulated enhancement (FIRE) mode to compare cases with and without fast ions during profile relaxation across five initial main-ion temperature gradients. We observe that fast ions induce larger zonal-flow and shearing-rate amplitudes, together with persistent shear layers. At the reference profile based on the experiment, these shear layers coexist with temperature-gradient corrugations qualitatively consistent with E× B staircases. When fast ions are present, inward and outward ion heat fluxes coexist at different radii, which causes the average heat flux to be smaller than when fast ions are absent. This redistribution of ion heat transport may be relevant to understanding the improved ion confinement observed in FIRE mode. In particular, we note a transition-like response in the presence of fast ions, whereby the heat flux decreases as the ion-temperature gradient increases, in contrast to the conventional Fick's law trend without fast ions. This behavior that deviates from Fick's law suggests that FIRE mode may represent a bifurcation to a distinct transport regime rather than a continuous high-performance extension of L-mode. These findings highlight the importance of the initial temperature gradient and global zonal-flow organization when assessing fast-ion effects on ion heat transport.
ER -