21 Holy Grail Materials Could Unleash Fusion Once and for All
One of the hardest engineering challenges in the world of fusion energy is developing materials that can withstand the inferno of a reactor’s plasma.
The International Thermonuclear Experimental Reactor (ITER) will be relying on tungsten as its plasma-facing material, but a new study explores whether other candidates could perform even better.
The research reveals a shortlist of 21 materials, which includes both some well-known candidates like tungsten and a few exotic examples that have yet to be studied.
The checkered flag at the end of humanity’s centuries-long energy race is fusion power, but bottling a star on Earth is about as difficult as it sounds. In recent years, scientists have successfully put theoretical physics to work by extracting more energy from a fusion reaction that they originally put in—an achievement known as “ignition”. But there’s a wide chasm between laboratory energy gains and real-world utility, and that chasm will need to be bridged by material breakthroughs.
As you can probably imagine, the environments inside these artificial stars are some of the most intense on Earth. Not only do the materials within have to withstand temperatures hovering around some 100 million degrees Celsius (seven times hotter than our Sun’s core), they also have to survive the strange atomic conditions that occur in a fusion environment.
Currently, scientists have landed on the element tungsten as the best candidate for the reactor’s divertor—a kind of exhaust port of heat and ash, and one of the few elements of a fusion reactor that interacts with the ultra-hot plasma directly. The International Thermonuclear Experimental Reactor (ITER), which is a fusion energy project in southern France that will be the most advanced reactor when its up and running, is using tungsten because of its ability to both withstand high temperatures and not retain fuel (i.e. tritium) as compared to other elements like carbon.
Although tungsten might be the element du jour, a new study from scientists at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland details the search for other plasma-facing materials that could perform even better than tungsten in future reactors. By analyzing the inorganic crystal structure found in the Pauling file database, the researchers crafted a shortlist of 71 materials and continued to eliminate elements based on past experiments or studies that ruled out certain candidates. They discovered that a viable candidate needed two important attributes: a high surface binding energy (it’s difficult for the material to lose atoms to the plasma) and formation energy of a hydrogen interstitial (the amount of energy it takes for tritium insertion into a lattice).
The results of the study were published in the journal PRX Energy.
“If a divertor material is excessively eroded during its operational lifetime, the released atoms disperse into the plasma, leading to a reduction in its temperature,” Andrea Fedrigucci, first author of the paper, said in a press statement. “In addition, if the material is chemically reactive with tritium, it can subtract the tritium available for fusion and cause an accumulation of tritium inventory that exceeds the safety limits imposed for this type of technology.”
The result of this winnowing of possible holy grail materials provided some expected results. Tungsten, for example, still made the list in both metallic and carbide forms. Diamond, graphite, boron nitride joined that list, as did transition metals like molybdenum, tantalum, and rhenium. However, there were a few surprises—particularly a phase of tantalum nitride, and certain ceramics based on boron and nitrogen.
Future studies can now investigate these materials as potential candidates for upcoming fusion reactors, and Fedrigucci hopes that neural networks can help simulate how they would hold up in the fiery bowels of a fusion reactor.
The race continues.
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