ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2025 1 7 Fig. 1 — Schematic of the CHADWICK Materials Discovery Process. encountered under fusion conditions. Deuterium tritium fusion reactions will generate up to 3.4 MeV alpha particles that can implant themselves into the first wall as well as 14 MeV neutrons that can cause n-α reactions to generate additional helium[11]. At high temperatures, helium will migrate to the grain boundaries and stabilize bubble formation and growth. The bubbles will weaken the grain boundary and cause premature failure. In a fusion environment, helium concentration is expected to be orders of magnitude higher than fission environments[12]. Any new material to be used as a fusion first wall must be exposed to a high helium concentration in addition to neutrons and high temperature to validate its performance. Plasma Erosion. Existing test tokamaks have seen a variety of erosion rates for vessel walls made from Be, C, Fe, Mo, and W, ranging from 1021 – 1022 atoms/s for low Z materials and 1022 – 1023 atoms/s for high Z materials. Assuming the plasma erodes the entire inside of a tokamak evenly, that converts to a 0.1 – 3.5 mm/yr erosion rate[13]. Plasma erosion has two major detrimental effects: it thins the plasma- facing materials, thereby reducing their performance, and it increases plasma impurity while decreasing plasma stability through eroded or vaporized material[14,15]. Understanding and managing the erosion rates of plasma- facing material is necessary to achieve sustained fusion reactions to generate electric power. TECHNOLOGY APPROACH TO DISCOVER FUSION FIRSTWALL MATERIALS The goal of the CHADWICK program is the discovery, development, and production of new materials that can achieve the following metrics in a fusion first-wall environment: • Room temperature ductility after 50 dpa of irradiation damage and helium generation • Sufficiently high thermal conductivity to remove up to 10 MW/m2 of heat • Activation below 10,000 Sv/hr to enable remote handling • Swelling below 1% to maintain dimensional stability • Tritium retention and plasma erosion lower than current state-of-the-art materials The CHADWICK program comprises three technical categories. Category A projects target the development of novel plasma-facing component materials; Category B teams focus on novel structural materials; and Category C projects support analysis and facilitate communication with end users for both Category A and B teams. A summary of 13 projects selected under CHADWICK is available on the ARPA-E site[16]. High Entropy Alloys (HEAs). High entropy alloys are a relatively new class of materials created by combining near-equal atomic percentages of more than three elements that maintain phase stability. The presence of different elements increases the entropy of mixing of the resulting alloy and can lead to improved properties not attainable in traditional alloys. The increased lattice distortion of the crystalline structure slows down diffusion and inhibits the nucleation and growth of irradiation defects. The strong solid solution strengthening of these alloys also makes them especially stable at higher temperatures and resistant to phase transformations. These theoretical advantages make HEAs ideal candidates for discovery and testing as fusion first-wall materials. Accelerated high-throughput screening
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