We investigate the dynamic evolution of edge-localized modes (ELMs) in the China Fusion Engineering Test Reactor (CFETR) under the influence of a biased divertor target plate system by using integrated numerical simulations. Combining magnetic field line tracing with the three-dimensional equilibrium code HINT and the nonlinear MHD instability code MIPS, we systematically evaluate the feasibility of employing a biasing system as an ELM control technique for CFETR. The results demonstrate that under an optimal bias configuration, a bias-driven scrape-off layer (SOL) current of 1000 A can significantly modify the pedestal pressure distribution and reduce the saturated kinetic energy of ELM-related instabilities by approximately 70%.

ELM control in H-mode operation is essential for future tokamak reactors such as CFETR, as uncontrolled Type-I ELMs can impose intolerable transient heat loads on plasma-facing components. Although resonant magnetic perturbation (RMP) is one of the most effective ELM control techniques, its implementation in reactor environments faces challenges of limited installation space and severe neutron irradiation. At the same time, the biased divertor approach provides a more reactor-compatible alternative by generating helical currents in the SOL without the need for in-vessel coils. In this work, a coupled HINT-MIPS modeling framework is used to evaluate the influence of bias-driven SOL currents on three-dimensional MHD equilibrium and edge instabilities in CFETR.

The simulations are based on a 13 MA hybrid H-mode equilibrium. A filament current model combined with magnetic field line tracing is used to calculate the spatial distribution of bias-driven SOL currents along magnetic field lines. The corresponding three-dimensional magnetic perturbations are then obtained by using the Biot-Savart law. Several representative bias configurations are examined, including “ ++\;++\;++\;++ ”, “ ++\;++\;++\;- ”, “ ++\;-\;++\;- ”, “ +-\;+-\;+-\;+- ”, and “ -+\;-+\;-+\;-+ ”. The analyses of the resonant magnetic spectra and magnetic topology reveal that the configuration with all electrodes biased positively exhibits the strongest resonant component at toroidal mode number n = 4, thereby maximizing the edge Chirikov parameter. Therefore, this configuration is identified as being optimal for further investigation.

Using the HINT code, we calculate three-dimensional nonlinear resistive equilibria for different SOL current amplitudes. These bias-driven magnetic perturbations lead to the formation of magnetic islands at rational surfaces and stochastic magnetic fields near the plasma edge, resulting in significant modifications of the pressure profile. The magnitude of pressure redistribution increases with SOL current amplitude increasing. These equilibrium changes directly affect the pedestal pressure gradient and thus the stability of edge MHD modes. After the initial 3D equilibrium is established, the MIPS code is used to simulate MHD instabilities. This code solves the full set of MHD equations in cylindrical coordinates.

Subsequently, based on the reconstructed three-dimensional equilibrium, the MIPS code is used to simulate the evolution of edge instability. As the SOL current increases from 0 to 1000 A, the linear growth rate and saturated kinetic energy of ELM-related instability decrease markedly, with the most pronounced stabilization occurring between 0 and 600 A. A further increase in SOL current yields diminishing return, suggesting a combined effect of nonlinear pedestal modification and the intrinsic nonlinear dependence of ballooning-type instabilities on pedestal structure. Pressure perturbation analyses confirm that the dominant modes are ballooning-like and that their amplitudes are strongly suppressed at higher SOL current levels.

These results clearly demonstrate the potential of biased divertor systems for effective ELM control in CFETR. The generation of SOL helical currents provides a promising and reactor-relevant pathway for mitigating edge instabilities and reducing transient heat loads in H-mode operation. In future work, we will extend this study by using the MARS-F code to incorporate detailed resistive plasma response effects.