Can theory and computational methods help find the best guiding material and thus make fusion power a reality?
The study of nuclear fusion as a clean energy source reveals the critical need for modern plasma materials. MARVEL laboratory researchers have identified materials that can withstand extreme fusion conditions and proposed alternatives to the current choice, tungsten.
Nuclear fusion and financial difficulty
Nuclear fusion offers a promising solution to our energy problems, with the potential to provide a virtually unlimited source of energy without greenhouse gas emissions. However, significant technological hurdles remain, especially regarding the materials required for fusion reactors. These reactors rely on materials that can withstand extreme conditions at the plasma interface.
The ITER project, an experimental European reactor under construction in southern France, includes a critical component called a diverter. This device extracts the heat and ash produced by the fusion reaction and directs an intense flow of heat and particles from the plasma to specific surfaces for cooling. The router’s plasma-coated materials must not only withstand extremely high temperatures, but also a constant bombardment of neutrons, electrons, charged ions and high-energy radiation.
Tungsten was chosen as the submersible for ITER due to its outstanding heat resistance. But other materials such as carbon fibers and ceramics have been considered before. Whether tungsten will continue to be the best choice for future reactors remains an open question, as researchers continue to explore alternatives that can better withstand the unique demands of fusion.
MARVEL laboratory’s computational approach
Can theory and computational methods help find the best guiding material and thus make fusion a reality? Scientists Nicola Marzari from the MARVEL Laboratory at EPFL set out to answer this question and published a new paper. PRX Energy They present a method for large-scale screening of potential plasma targeting materials and a short list of the most promising ones.
First of all, scientists needed to find a way to make informatics accessible for treatment. “To realistically simulate the dynamics at the plasma-material interface, you need to simulate the behavior of thousands of atoms for a few milliseconds, which would be impossible with conventional computing power,” says Andrea Fedrigucci, a PhD student in the THEOS laboratory and first author of the paper. “So we decided to pick a few key properties that a plasma coating material should have and use them as an indicator of how well this material could work in a router.”
First, the scientists looked at the Pauling File Database, a large collection of known inorganic crystal structures, and created a workflow to find ones with sufficient resistance to withstand the temperatures in the reactor. This can be understood by looking at their heat capacity, thermal conductivity, melting point and density. Since the surface temperature of a layer of material depends on its thickness, they also calculated the maximum thickness each material could have before melting and ranked the materials accordingly. They used the Pareto optimization method to classify materials for which maximum thickness information could not be calculated according to the previously mentioned properties.
The election process begins
The result was an initial shortlist of 71 candidates. At this stage, it was necessary to use a very inexpensive and old method.
“I patiently reviewed the literature on each to see if they had been tested and discarded before, or if there were properties that precluded their use in a fusion reactor that were not in the database, such as a tendency to corrode or deteriorate their thermal properties during bombardment with plasma and neutrons.”
Interestingly, this part of the research resulted in the rejection of some innovative materials proposed for use in fusion reactors, such as high-entropy alloys, as diverter materials.
Final selection of promising materials
In the end, we were left with 21 materials to which the DFT workflow was applied to calculate two key properties that a good plasma fusion material should have: surface binding energy, which is a measure of how easily an atom can be attracted from a surface. and hydrogen interstitial formation energy, which measures the solubility representation of tritium in the crystal structure.
“If the guiding material degrades excessively during its lifetime, the released atoms will disperse in the plasma, causing its temperature to drop,” says Fedrigucci. “Additionally, if the material reacts chemically with tritium, it could eliminate tritium available for fusion and cause tritium stocks to accumulate beyond the safety limits established for this type of technology.”
As a result, the final ranking based on all important properties includes some of the usual suspects that have been extensively tested: Tungsten itself in its metallic (W) and carbide forms (WC and W)2C), diamond and graphite, boron nitride and transition metals such as molybdenum, tantalum and rhenium. But there were a few surprises, too, such as a special tantalum nitride phase or other boron-nitrogen-based ceramics that have never been tested for this application.
In the future, the group hopes to use neural networks to better model what actually happens to materials in the reactor, including interactions with neutrons that cannot be modeled here, Fedrigucci said.
Source: Port Altele
