Gyrokinetic global simulation of Alfvénic ion temperature gradient mode in reversed magnetic shear
Gengxian Li, Zhixin Lu, Philipp Lauber, Matthias Hoelzl, Guo Meng, Yong Xiao
Abstract
Abstract In this work, a systematic study of electromagnetic instabilities driven by the temperature gradient in magnetically confined fusion plasmas with reversed magnetic shear is conducted using gyrokinetic particle-in-cell simulations. An electromagnetic instability arising in the low- β regime is investigated, where β = 8 π n T / B 2 denotes the ratio of plasma pressure to magnetic pressure. Within a reversed shear safety factor ( q ) profile, when a mode rational surface coincides with the position of zero shear, an instability dominated by only one poloidal harmonic emerges, rather than the conventional ion-temperature-gradient (ITG) mode. Simulation results demonstrate that the instability exhibits pronounced electromagnetic polarization even in the low- β regime, with a real frequency significantly higher than that of ITG modes, and show that it is destabilized by the temperature gradient and not by the density gradient. This instability can be observed even for a monotonic q profile with weak magnetic shear. Based on a systematic comparison with other typical electrostatic and electromagnetic instabilities, this instability is identified as a weak shear Alfvénic-ITG (WSAITG) mode, which may provide an explanation for the low-frequency Alfvén modes (LFAM) observed in experiments. Wave–particle resonance analysis in phase space reveals that, in contrast to the ITG mode, well-passing particles provide an additional resonant population that drives the WSAITG mode.
BibTeX
@article{Li_2026,
title={Gyrokinetic global simulation of Alfvénic ion temperature gradient mode in reversed magnetic shear},
volume={66},
ISSN={1741-4326},
url={http://dx.doi.org/10.1088/1741-4326/ae9324},
DOI={10.1088/1741-4326/ae9324},
number={9},
journal={Nuclear Fusion},
publisher={IOP Publishing},
author={Li, Gengxian and Lu, Zhixin and Lauber, Philipp and Hoelzl, Matthias and Meng, Guo and Xiao, Yong},
year={2026},
month=Aug,
pages={096035} }