Disruption damage to plasma-facing components from various plasma instabilities

Damage to plasma-facing components and structural materials of fusion reactors during abnormal plasma instabilities such as hard disruptions, edge-localized modes (ELMs), and vertical displacement events (VDEs) is considered a serious life-limiting concern for these components and materials. Plasma-facing components (PFCs) such as the divertor, limiter, and first wall will be subjected to intense energy deposition during these plasma instabilities. High erosion losses of material surfaces, large temperature increases in structural materials, and high heat flux levels and possible burnout of coolant tubes are critical issues that severely limit component lifetime and therefore diminish reactor safety and economics. A comprehensive model that integrates various stages of plasma interaction with plasma-facing materials (PFMs) is extended to analyze and evaluate the damage that results from various plasma instabilities. Models for thermal evolution and phase change of a multilayer structural material, for the developed vapor cloud magnetohydrodynamics above the surface of the material, and for calculating the resulting radiation and its transport through this vapor cloud due to plasma/vapor interaction are dynamically coupled in a self-consistent way to evaluate various aspects of detailed time-dependent responses of PFMs. The extent of the damage to PFMs, structural materials, and coolant channels depends mainly on the total deposited plasma energy, deposition time, and the coating or surface material. During short disruption events (tau(c) less than or equal to 1 ms), the initially intense evaporated material can significantly shield the PFM and reduce its further erosion. When plasma instabilities occur at longer durations, however, such as in VDEs (tau(d) approximate to 100-300 ms), no significant self-shielding is expected; therefore, serious erosion and melting can occur. In addition, hydrodynamic instabilities and other mechanisms will further erode melt layers of metallic PFMs. Plasma instabilities of longer duration may also allow more time for conduction of deposited plasma energy from the surface to the structural material and finally to the coolant channels, where it can cause burnout. These events are analyzed parametrically for the expected range of plasma parameters for various surface materials such as beryllium, carbon, and tungsten, and for structural materials such as copper.