Tokamak discharge simulation for EAST by coupling METIS and free-boundary equilibrium code FBT

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Abstract Fast and reliable discharge modeling is an essential tool for tokamak scenario development, as extensive simulations are required to explore the feasible operational space and translate physical targets into implementable actuator waveforms. In this work, a fast discharge simulator for Experimental Advanced Superconducting Tokamak (EAST) was developed by coupling the fast integrated tokamak modeling tool METIS with the free-boundary equilibrium code FBT from the MEQ (Matlab EQuilibrium) suite. METIS provides the evolution of the plasma profiles by self-consistently solving heat and particle transport with source profiles. The generated outputs are then used directly in FBT to computes the poloidal field (PF) coils currents needed in order to obtain a given plasma shape. The coupling strategy is based either on matching the free functions ( p ′ ( ψ ) and F F ′ ( ψ ) ) on the right-hand side of the Grad–Shafranov equation, or on matching global quantities such as the plasma current I p and stored energy W MHD . Both approaches are effective in ensuring consistency of the pressure and current-density profiles between the two codes. The last closed flux surface (LCFS) curve computed by FBT is fed back into METIS to update the LCFS, and METIS is then run again. The METIS – FBT iteration is repeated until convergence is reached. The results obtained with the equilibrium code FBT are first benchmarked against experimental data and reconstruction results available on EAST. The coupled METIS-FBT workflow is then assessed through a post-shot simulation of an radio-frequency heated EAST discharge, showing its ability to reproduce the main plasma evolution and generate inverse free-boundary PF-coil current trajectories consistent with experimental references. Its predictive scenario-design capability is further demonstrated through the design of a synthetic discharge scenario.

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