This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Fusion reactors, devices that generate energy by fusing light atomic nuclei at extremely high temperatures, could contribute to ongoing efforts aimed at producing electricity more sustainably. The extreme environment inside these devices, however, can damage materials that surround the superheated, electrically charged plasma where the nuclear fusion reaction takes place.
One possible source of damage stems from the production of neutrons, electrically neutral particles released during fusion reactions. When a high-energy neutron strikes an atom, it can knock it out of its typical position. The displaced atom can then collide with other atoms and prompt them to also leave their original positions, resulting in what is known as primary radiation damage.
Researchers at the University of Helsinki recently ran a series of molecular dynamics simulations to better understand how atoms move and interact during these collisions, particularly focusing on tungsten. Their paper, published in Physical Review Letters, offers new insight into what might happen to tungsten at the extreme energies inside fusion reactors. "The project began as a part of our effort to adapt our machine-learning simulation model to run efficiently on graphics processing units (GPUs)," Jesper Byggmästar, first author of the paper, told Phys.org.
"After that we realized we can run much larger and more accurate simulations than ever before. We decided to find out what kind of damage is created if one irradiates tungsten with extremely high-energy ions." The main goal of this recent study was to better understand how extreme radiation affects tungsten, one of the most promising materials for the fabrication of reactor components. One way of measuring primary radiation damage involves counting the number of atoms knocked out of their normal positions after one atom is hit by a high-energy neutron.
"In metals, current models assume that the number of defects first increases sublinearly with increasing recoil energy, and then linearly," explained Byggmästar. "We found that in tungsten, the trend goes from sublinear to superlinear and finally to linear. Observing and quantifying all these transitions required atomistic simulations (molecular dynamics) at unprecedented scales in this field, reaching the milestone of simulating one billion atoms at once." Byggmästar and his colleagues ran extremely large simulations, using a machine-learning model to reliably reproduce the molecular dynamics of tungsten and the physical processes unfolding in the material.
Their simulations suggest that when approaching the extremely high energies that would be found inside fusion reactors, tungsten components would deteriorate more than originally anticipated. "There are two major achievements in our paper, one with technical implications and the other with scientific implications," said Byggmästar. "We demonstrated that accurate billion-atom simulations not only are technically possible but also useful for exploring and revealing new physics.
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