Phase-field modeling of thermomechanical damage in tungsten under severe plasma transients

Abstract

Tungsten is now a primary candidate for plasma facing components in fusion energy systems because of its numerous superior thermophysical properties. International efforts are currently focused on the development of tungsten surfaces that can intercept ionized plasma and pulsed high heat flux in magnetic fusion confinement devices. Thermal shock under transient operating conditions, such as edge localized modes, have experimentally been shown to lead to severe surface and sub-surface damage. We present here a computational multiphysics model to determine the relationship between the thermomechanical loading conditions and the onset of damage and failure of tungsten surfaces. The model is based on thermo-elasto-plasticity constitutive relations, and is developed within the framework of the phase-field method. A coupled set of partial differential equations is solved for the temperature, displacement, and a damage phase fields under severe plasma transient loads. The results clearly show the initiation and propagation of surface and sub-surface cracks as a result of the transient high heat flux. The severity of surface cracking is found to correlate primarily with the magnitude of the near-surface temperature gradient.