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The linear properties of the 2/1 drift-tearing mode (DTM) are verified within the framework of the MAS global eigenvalue code Bao et al., Nucl. Fusion 63, 076021 (2023). This code provides a hierarchy of physics models with kinetic effects beyond magnetohydrodynamics (MHD) in toroidal geometry. To compare with theory, a concise drift-MHD model is adopted in the MAS global simulations of DTMs. In the regime of small electron diamagnetic drift (EDD) frequency |ω∗n,e|≤γc, where γc is the classical resistive tearing mode (RTM) growth rate, the DTM growth rate and real frequency obtained from global simulations agree well with local theory, and the mode structure resembles that of the RTM. However, when the EDD frequency exceeds a critical threshold (|ω∗n,e|≥|ω*n,ecrit|∼2γc), the DTM growth rate increases with increasing |ω∗n,e|, deviating qualitatively from local theory. Meanwhile, the δϕ perturbation becomes dominated by short-wavelength radial oscillations, whereas the δA|| perturbation retains the macroscopic structure characteristic of the RTM. This discrepancy in DTM destabilization is attributed to global effects and is consistent with the drift-tearing wave-packet solution from earlier slab geometry simulations. In contrast to the EDD effects, the ion diamagnetic drift effect only stabilizes the RTM, showing excellent agreement between global simulation and local theory.
Chen et al. (Mon,) studied this question.