Speaker
Description
High-energy plasma interacting with plasma-facing components (PFCs) causes surface damage (e.g., vaporization, sputtering) via intense heat and particle fluxes, compromising reactor lifetime, performance, and safety. Effective PFCs require properties like low sputter yield, high melting point, thermal conductivity, moderate activation, and low gas permeation. Meeting diverse, location-specific requirements (e.g., first wall demands versus divertor's need for high heat load resistance) is a major material challenge.Tungsten (W) is a primary candidate for PFCs, offering high thermal conductivity, sputtering threshold, and melting temperature, but its embrittlement, particularly from overheating, is a significant drawback. As fusion technology advances, demands for power exhaust and lifetime continue to rise. In light of these challenges, this study aims to qualify W components for the COMPASS-U device, specifically focusing on its inertial W components in the divertor region. These components employ W high thermal inertia to resist and manage intense, rapid thermal loads from the plasma. Therefore, evaluating their performance under steady-state and transient heat loads, understanding material evolution, microstructure, surface condition, and D2 retention characteristics is critical. W samples (Plansee) were exposed to plasma in the PSI-2 facility and characterized post-exposure by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), and fuel retention measurements via Thermal Desorption Spectroscopy (TDS) in a high vacuum system up to 1700 °C. A Pfeiffer mass spectrometer monitored gas release, with simultaneous temperature tracking (pyrometer, type-C thermocouple). Samples underwent 100,000 laser pulses (0.5 ms, 0.4 GW/m²) while exposed to D2/He (6%) plasma (flux 3.2 × 10²¹ m⁻² s⁻¹), with a total fluence of 3.4 × 10²⁵ m⁻² at 700 °C. After initial exposure, samples were heated to 1000 °C (1 hour) to outgas, then exposed to D2 plasma (flux 3.7 × 10²¹ m⁻² s⁻¹, 1 hour), accumulating a total fluence of 1.4 × 10²⁵ m⁻² at ~300 °C. AFM and SEM characterization revealed significant cracking and surface roughening on laser-damaged samples, contrasting with smoother surfaces after only D2 plasma exposure. Despite these severe microstructural changes, total desorbed deuterium for laser-damaged samples was approximately 9.8 × 10¹¹ atm/cm² (peak desorption at 896 K). This retention level showed no increase compared to plasma-only exposed samples (1.276 × 10¹² atm/cm²). This comparative analysis comprehensively evaluates combined laser and plasma damage effects on W microstructure and fuel retention, offering key insights for COMPASS-U W divertor components.