Speaker
Description
A number of advanced tungsten (W) based and chromium (Cr) plasma-facing materials were exposed to reactor-relevant divertor plasmas in the DIII-D tokamak using the Divertor Materials Evaluation System (DiMES). The objective was to evaluate the surface response and thermo-mechanical performance of next-generation divertor materials under steady-state and transient heat loads typical of future power-plant operation.
The 5 cm diameter DiMES holder contained seven 6 mm diameter samples, some of them angled at 10º towards the incident heat and particle fluxes to reach more reactor-relevant conditions. The materials tested included micro-structured W (2 angled samples), long- and short- W fiber strengthened W (Wf/W, angled and flat, respectively), a flat W sample strengthened with W and silicon carbide (SiC) fibers (WfSiCf/W), and two flat Cr samples. The experiment was performed in H-mode deuterium discharges with Bₜ ≈ 2 T, Iₚ ≈ 1.1 MA, and up to 4.5 MW of neutral-beam heating, producing average incident heat fluxes of ~4.5 MW m⁻² on flat surfaces and ~15 MW m⁻² on 10° angled surfaces. A 5 cm outer strike point sweep over DiMES at ~2 Hz minimized spatial variation in the incident heat flux and provided near-uniform (within 15-20%) exposure conditions for all samples. Diagnostics included IR thermography, filtered visible imaging and spectroscopy to capture sample surface temperature and erosion during the plasma exposures.
Preliminary analysis of spectroscopic data and post-exposure microscopy indicates that both angled micro-structured tungsten and tungsten fiber-based composites maintained structural integrity, with minor edge melting and cracking, but no observable major crack propagation. The flat WfSiCf/W sample exhibited localized surface smoothing and minor fiber-interface restructuring but preserved bonding and toughness, demonstrating efficient energy dissipation through SiC interlayers. The chromium sample showed the least surface changes; only light surface erosion was observed and emission near Cr-I lines, enabling initial benchmarking of gross erosion and redeposition models.
These results confirm that micro-structuring and composite approaches to improving W properties exhibit superior resilience to transient and cyclic heat loads, while chromium’s radiative properties and controlled erosion behavior make it a viable candidate for passively mitigating divertor heat flux. The experiment provides crucial input toward down-selection and modeling validation for FPP plasma-facing material strategies.
Work supported by the Department of Energy under Award Numbers DE-FC02-04ER54698, Sandia National Laboratories: DE-NA0003525, Princeton Plasma Physics Laboratory: DE-AC02-09CH11466. This work/co-authors received funding from the EUROfusion Consortium via the Euratom Research and Training Programme (Grant No. 101052200)