Coupled Modeling for Self Consistent Equilibrium Evolution Using the IPS Framework

Changes in magnetic fields resulting from plasma perturbations, induce currents in structures of magnetic confinement devices. These eddy currents in turn, affect the equilibrium. Modeling the plasma evolution under such conditions, requires calculating the resulting equilibrium in a self consistent manner. Since port openings, heating antenna, diagnostics, etc., break the axisymmetry induced eddy currents will cause 3D effects on the equilibrium. To model this self consistently a workflow using the Integrated Plasma Simulation (IPS)[1] framework was developed to couple VMEC[2] with eddy current response functions calculated from CARIDDI[3]. IPS is a python framework for creating coupled workflows that can be run on high performance computing (HPC) systems. IPS provides functionality to coordinate input and output states, manage compute resources, and define dependencies between components. Wrapping physics codes as IPS components simplifies the task of integrated modeling. Using IPS self consistent 3D equilibria are computed using an iterative approach. VMEC is a fully 3D equilibrium solver that minimizes MHD energy by enforcing force balance. VMEC can find an equilibrium consistent with external field coils by enforcing an edge force balance with vacuum field contributions. Eddy current contributions, computed by CARIDDI on a 3D volumetric finite elements mesh, are added by including the vacuum contribution in the edge force balance. Starting from no eddy contribution, an equilibrium is computed. Using a fixed coupling surface, a virtual surface current is computed onto it. Then through a series of precomputed response matrices that only depend on the static geometry, a vacuum contribution is computed. A new equilibrium is calculated using this new vacuum fields. This procedure is repeated until the system converges to a stationary self consistent equilibrium and eddy current.