Vertical displacement events: A serious concern in future ITER operation

Material damage to plasma-facing components due to the frequent loss of plasma confinement remains a serious problem for tokamak reactors and in particular for ITER-like design. The deposited plasma energy during major disruptions, edge-localized modes (ELM), and vertical displacement events (VDE) causes significant surface erosion, possible structural failure, and frequent plasma contamination. Surface erosion damage consists of vaporization, spallation, and liquid splatter of metallic materials. Structural damage includes large temperature increases and high thermal stresses in structural materials and at the interfaces between surface coatings and structural components. A comprehensive fully 3D model (contained in the HEIGHTS computer simulation package) is developed to specifically study the longer plasma instabilities that cause VDE. The model includes detail deposition processes, surface vaporization, phase change and melting, heat conduction to coolant channels, and critical heat flux criteria at the coolant channels. The design requirements and implications of plasma-facing components are discussed along with recommendations to mitigate and reduce the effects of plasma instabilities on reactor components.