FreeMHD: experimental validation of a fully-3D-non inductive-MHD solver for liquid metal flows in fusion devices*

Liquid metals (LM) are an alternative to solid plasma-facing components in divertors of fusion reactors, where melting and erosion has been observed. LM flows could exhaust heat from the plasma through advection (fast-flow regime) or by conduction to a substrate (slow-flows regime). Free-surface-LM flows inside nuclear-fusion-reactor conditions have been considered for this purpose. However, the analysis of this type of flows under strong magnetic fields through simulations has been a challenge due as extremely thin Hartmann layers in the flow and ripples at the free surface could make numerical convergence unattainable. 

FreeMHD is a fully three-dimensional and transient numerical tool for the simulation of free surface, thermo-MHD phenomena is developed in the framework of the finite volume method and implemented using the OpenFOAM open-source toolkit. It provides a new simulation tool that has been recently developed. FreeMHD is the first simulation code validated against a series of experiments under different MHD conditions while varying: substrate conductivity and thickness, applied external currents and magnitude of external magnetic fields. These experiments were executed in the Liquid Metal eXperiment - Upgrade (LMX-U) and in the Liquid Metal FRee-surface EXperiment (LMFREX) at the Oroshhi-2 Superconducting Magnet Facility of the National Institute for Fusion Science (NIFS). Additionally, simulations at the reactor scale were executed, which evidences the code stability at strong magnetic fields.