Speaker
Description
A coordinated campaign of experiments in the DIII-D tokamak has advanced the qualification of plasma-facing materials (PFMs) through national laboratory and university efforts together with public–private partnerships. Candidate materials included W alloys, additively manufactured (AM) W, K-doped W, neutron-irradiated W and ceramics, high-entropy and multi-principal-element alloys, ultra-high-temperature ceramics, SiC-based composites, and boron-based concepts. These were exposed to reactor-relevant heat and particle fluxes using the Divertor Materials Evaluation System (DiMES), providing a bridge between bench-scale testing and integrated plasma–material interaction conditions expected in ITER and future pilot plants (FPPs). The campaign establishes a rapid, repeatable pathway for qualifying industry-developed materials directly under reactor-relevant tokamak conditions.
Bulk W, cold-sprayed Ta and Ta–W alloys, AM W with varied grain structures, and K-doped W were tested under H-mode plasmas. Inter-ELM heat fluxes of 2.2–2.4 MW/m² and transient ELM loads up to ~6 MW/m² were achieved, with angled samples intercepting >10 MW/m². Surface temperatures near 800 °C were recorded. Large-grain AM W exhibited reduced cracking vs ITER-grade references, while K-doped W maintained structural integrity at 750–780 °C. Alloying constituents showed selective erosion, providing new benchmarks for erosion modeling. W samples with controlled orientations (001 vs 111) reached >1500 °C in angled exposures, crossing the recrystallization threshold and enabling comparison of texture-dependent cracking and erosion. Orientation strongly influenced recrystallization onset and erosion rates, offering guidance for optimizing AM processing routes. Neutron-irradiated W and ceramic samples were also tested, probing coupled effects of irradiation damage and plasma loading.
Advanced W alloys, refractory multi-principal-element alloys, and renewable boron pebble–rod components were also qualified under integrated plasma conditions. Exposures reached inter-ELM heat fluxes of 2.2–2.5 MW/m² with surface temperatures of 600–700 °C and extended up to 15 MW/m² for angled geometries. In-situ spectroscopy identified selective erosion of alloying constituents, while boron pebble–rod prototypes demonstrated controlled boron release without plasma termination. SiC fiber composites withstood ~2.0 MW/m² in ELMy H-mode with moderate microstructural modification, while monolithic ceramics such as Si₃N₄ and B₄C proved more fragile, showing partial ejection during ELMs without major plasma impact.
These experiments, together with those from the first DIII-D materials campaign, constitute one of the most comprehensive qualifications of advanced PFMs in a tokamak environment to date. They provide mechanistic insights into cracking, recrystallization, selective erosion, and controlled material release under transient H-mode conditions, and they establish new benchmarks for modeling, accelerate materials down-selection, and inform the design of plasma-facing components for ITER and FPPs.