Impact of electron inertia on edge-localized mode simulation using the BOUT++ six-field two-fluid model

The impact of electron inertia on edge-localized mode (ELM) simulations using the BOUT++ six-field two-fluid model is investigated in this work. Electron inertia is found to have a negligible effect on the simulated linear growth rates under typical tokamak edge plasma conditions. Further analysis based on the ideal magnetohydrodynamic model indicates that the destabilizing effect of electron inertia (as a high-order term) could be overestimated unless the related low-order terms, such as the electron pressure gradient term, are considered as priors. For nonlinear simulations with toroidally axisymmetric parallel current evolution, the ELM burst can be successfully simulated without additional hyper-resistivity by including electron inertia. The size of the simulated ELM lies between those simulated with a constant hyper-resistivity of 10−14 and 10−13. Radial spectrum analysis demonstrates that during the nonlinear phase, when the high-wavenumber components regarding the formation of narrow current sheets become considerable, the effect of electron inertia is non-negligible. It is found that the dominant dissipation mechanism is electron momentum convection and the effect can be represented by spatiotemporally varying effective hyper-resistivity, with the highest value in the range between 10−14 and 10−13. Furthermore, it is also found that computational efficiency during the nonlinear phase can be improved when electron inertia is included.