Coupled transport and turbulence simulation of grassy ELM cycles within the edge plasma coupling simulation (EPCS) framework

Abstract Small edge-localized mode (ELM) regimes, such as grassy ELMs, provide an operational solution for mitigating large transient heat fluxes on the divertor and first wall in future tokamak fusion reactors. Utilizing the recently developed edge plasma coupling simulation framework (Liu et al 2025 Plasma Phys. Control. Fusion 67 055004), a time-dependent coupled transport and turbulence simulation workflow is established and applied to simulate the grassy ELM observed in EAST discharge (Yang et al 2020 Nucl. Fusion 60 076012). The simulation result shows the periodical cycle of the plasma pressure with a frequency of ∼1.6 kHz, which is consistent with the experimental ELM frequency of ∼2 kHz. On the peeling–ballooning diagram, the counterclockwise rotating trajectory of the plasma evolution indicates that the grassy ELM regime is near the peeling boundary, which is consistent with the findings from linear stability analysis (Xu et al 2019 Phys. Rev. Lett. 122 255001). It is also found that the nonlinear evolution is primarily driven by low- n (where n means the toroidal mode number) modes concentrated at the pedestal foot. The strong particle transport at the pedestal foot in the simulation can be related to the positive phase difference between the density and electric potential fluctuations.