Three-dimensional nonlinear modeling of ELM dynamics with biasing in HL-3 tokamak

The influence of a biased divertor target system on Edge Localized Mode (ELM) dynamics is investigated for the first time in the HL-3 tokamak, focusing on the impact of bias-driven scrape-off layer (SOL) helical currents on three-dimensional (3D) magnetohydrodynamic (MHD) equilibria and instabilities. In a designed 1.6 MA H-mode discharge scenario, the applied SOL currents are modelled as filamentary currents aligned with magnetic field lines near the separatrix, and the resulting 3D perturbed magnetic fields are computed using Biot–Savart law. Nonlinear resistive equilibrium simulations with the HINT code show that the bias-driven currents significantly alter the pressure distribution and magnetic topology near resonant rational surfaces and in the edge stochastic layers, particularly in the pedestal region. Subsequent 3D nonlinear MHD instability analysis using the MIPS code reveals that the growth rate of edge instabilities systematically decreases with increasing SOL current, with a marked reduction observed at 1 kA. Additionally, nonlinear interactions between the external perturbations and intrinsic ballooning modes lead to a redistribution of the mode energy. These results demonstrate the potential of divertor biasing as a viable technique for ELM control in HL-3, offering a promising strategy for controlling edge instabilities and managing heat flux distribution in mega-ampere plasma current H-mode scenarios.