Speaker
Description
Fabricating fusion pilot plant (FPP) first-wall components through additive manufacturing (AM) could enable cost-effective, scalable production of complex, functionally graded components. In addition, optimized AM processes can produce materials that retain, and in some cases improve, the key thermo-mechanical properties needed in an FPP, relative to conventionally processed tungsten.
To evaluate whether additively manufactured tungsten (AM-W) can match or exceed bulk-W performance, AM-W, produced by laser powder bed fusion (LPBF; ~95% theoretical density, increased porosity relative to bulk W), was exposed to L- and H-mode plasmas using the Divertor Materials Evaluation System (DiMES) in the lower divertor of the DIII-D tokamak. The specimens were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), laser confocal microscopy, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) before and after exposure. Plasma conditions consisted of steady-state inter-ELM heat fluxes of 1.1-1.3 MW/m2 in L-mode and 1.4-1.6 MW/m2 in H-mode, with ELMs reaching 3.5-4.0 MW/m2. Results were benchmarked against conventionally manufactured pure tungsten reference samples irradiated under identical conditions.
Initial laser confocal microscopy surface analysis using the arithmetic mean height (Sa) showed AM-W experienced a greater increase in surface roughness after L-mode exposure than bulk-W, which exhibited minimal change. AM-W and bulk-W saw similar increases in surface roughness post H-mode plasma exposure, exceeding those from L-mode. XRD analysis shows no observable changes in both bulk-W and AM-W pre- and post-exposure, in L-mode and H-mode. XPS analysis indicates metallic W and stable WO3 pre-exposure, and similar trends post-exposure, with changes in oxide composition due to sputtering and contamination, observed in both L- and H-mode. EDS shows carbon deposition on both bulk-W and AM-W specimen features, expected from DIII-D operations. SEM indicates no surface crack evolution in AM-W samples post-L-mode exposure, some surface crack evolution in AM-W post-H-mode exposure. Surface analysis showed general robustness of the additively manufactured tungsten across experimental conditions at DIII-D.
Deuterium retention in the AM-W will be further determined through thermal desorption spectroscopy (TDS), using a custom-built facility being developed at UW-Madison. These findings represent a key step towards validating AM-W as a potential next-generation material for FPP first-wall applications.
This work was supported by US DOE under DE-NA0003525, DE-AC02-09CH11466, DE-FC02-04ER54698, DE-AC05-00OR22725, DE-AC52-07NA27344 and DE-SC00020428.