Simulation of edge-localized mode using BOUT ++ six-field two-fluid model including toroidal axisymmetric electric field and parallel current evolution

During BOUT++ simulations for edge-localized modes (ELMs), the electric potential is generally calculated using the flute-ordering one-dimensional Laplace solver. However, it is not valid for the toroidal axisymmetric (i.e., toroidal mode number n = 0) component, leading to the limitation on evolving n = 0 electric field and parallel current. Recently, to evolve the n = 0 electric field and plasma current, Seto et al. [Phys. Plasmas 26, 052507 (2019)] have adopted the two-dimensional Laplace solver to calculate the n = 0 electric potential and indicate the ELM evolution can be significantly affected. In this work, based on the EAST upper single null equilibrium, ELM simulation using BOUT++ six-field two-fluid model with n = 0 electric field and parallel current evolution is performed. Compared to the case with fixed n = 0 parallel current (∼5%) and net-drift-flow-free n = 0 electric field (∼7%), the simulated ELM size is significantly reduced (∼2%) and more consistent with the small ELM observed in experiment. Further analysis indicates that the reduction of simulated ELM size is mainly because: (1) the decrease in the n = 0 parallel current density during the nonlinear phase leads to the reduction of instability drive, causing smaller initial crash; (2) the relatively strong radial electric field shear suppresses the turbulence transport.