2025 – Tungsten DiMES Experiment

Tungsten DiMES Experiment

2025 Research Campaign, Thrust: FPP Candidate Wall Materials

Purpose of Experiment

This experiment investigates the performance of various advanced tungsten materials under reactor-relevant particle and heat fluxes in the DIII-D divertor, focusing on enhancing tungsten as a plasma-facing material. The test matrix includes cold-sprayed W-Ta coatings, additively-manufactured pure W, Ta-Ti-V-W refractory high-entropy alloys, nanocrystalline W-Ti-Cr alloys, additively manufactured W-Ti-Fe alloys, and K-doped and Re-doped W materials. Our hypothesis posits that these innovative strategies will improve microstructural stability and reduce cracking compared to high-purity, coarse-grained tungsten, with minimal impacts on sputtering performance and hydrogen isotope retention. Post-test characterization will assess microstructural changes, cracking behavior, and surface modifications, while also measuring hydrogen isotope retention and redeposited material. The findings aim to address the challenges of developing materials for fusion environments, providing critical insights for further optimization and advancing techniques for on-site repair and fabrication of wall materials. Ultimately, this research will contribute to the validation of numerical modeling tools for particle erosion and retention, as well as evaluate high-performance alloys for future fusion reactors.

Experimental Approach

The experiment will employ the Divertor Material Exposure Station (DiMES) within the DIII-D tokamak to subject small samples of advanced tungsten materials L-mode and H-mode plasmas with ELMs. The materials selected for testing comprise: • Cold-sprayed W-Ta coatings on 316L stainless steel (University of Wisconsin-Madison) • Additively-manufactured pure W (University of Wisconsin-Madison) • Ta-Ti-V-W refractory high-entropy alloy (University of Wisconsin-Madison) • Nanocrystalline W-Ti-Cr alloys (Stony Brook University) • Additively manufactured W-Ti-Fe alloys (Northwestern University) • K-doped and Re-doped W materials (Allied Materials, ALMT) The rationale underlying the materials selection for this study focuses on several advanced tungsten-based options aimed at enhancing performance in fusion reactor environments. Cold-sprayed W-Ta films, produced using a cost-effective and well-understood method, demonstrate effective deposition on stainless steel substrates, with tantalum aiding in adhesion and acting as a hydrogen getter. Refractory high-entropy alloys (RHEAs) composed of equimolar Ta-Ti-V-W are designed to outperform traditional tungsten by exhibiting superior resistance to extreme conditions, with testing planned for deuterium retention and high ion fluxes. Additionally, self-ion irradiated bulk tungsten samples will be analyzed for their thermal transport properties after exposure to reactor-relevant conditions. Collaborations with Stony Brook University and Northwestern University focus on nanostructured W-Ti-Cr and W-Ti-Fe alloys, which leverage nanostructuring for enhanced thermal stability and radiation tolerance. Lastly, the incorporation of K and Re dopants in tungsten materials aims to suppress increases in ductile-to-brittle transition temperature (DBTT) following ion irradiation, contributing to the development of high-performance materials for plasma-facing components in future fusion reactors. The DiMES probe will allow for exposure of these materials to elevated heat and particle fluxes, replicating the conditions found in a fusion reactor divertor. The experimental configuration will incorporate a total of 4 DiMES heads featuring both flush and angled samples, which will be subjected to high-power H-mode discharges with ELMs conditions to allow for the evaluation of erosion, thermal stability, and alterations in surface morphology. In addition, lower power L-mode plasma discharges will be used to evaluate the materials for hydrogen retention and sputtering behavior. Post-exposure analyses will encompass scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), thermal desorption spectroscopy (TDS), and various spectroscopic techniques to assess surface damage, compositional changes, and deuterium retention. The findings from these evaluations will guide the optimization of tungsten-based materials for enhanced performance in the harsh conditions of a fusion reactor. By combining these different techniques, the experiment seeks to deliver a thorough understanding of the performance and optimization potential of advanced tungsten-based materials for future fusion reactors.

Interested in a behind-the-scenes look at DIII-D? Join us for a virtual OR in-person tour during Fusion Energy Week (May 5-9)! Sign up for a tour here.

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