Discipline: Technology and Engineering
Subcategory: Materials Science
Room: Exhibit Hall A
Kenneth Distefano - Missouri University of Science and Technology
Co-Author(s): Brandon S. Laufer, University of Missouri, MO; Karl D. Hammond, University of Missouri, MO
Nuclear fusion has the potential to provide sustainable energy without significant harmful emissions into the environment and without the highly-radioactive spent fuel associated with nuclear fission. During a deuterium tritium fusion reaction, two hydrogen isotopes fuse together to produce helium (4He) and a free neutron. Magnetic-confinement fusion reactors, such as the ITER reactor currently under construction in France, seek to confine hot plasma in the core using magnetic fields. The neutrons produced by the reaction, which are not affected by the magnetic field, carry most of the energy into the first wall. The helium products, which respond to the magnetic field, are primarily directed at the divertor near the bottom of the reactor, though some neutrons interact with the divertor as well. When helium from the plasma impinges on the divertor – which will be made of tungsten because of its high melting point and favorable heat transfer properties – it becomes trapped under the surface and forms bubbles. We expect that these bubbles will burst, or at least change shape, when neutrons from the plasma interact with tungsten atoms near the bubble and/or with helium atoms in the bubble itself. We simulate neutron collisions with tungsten atoms by imparting high velocity in a random direction to one tungsten atom in a molecular dynamics simulation, then observe the resulting trajectory and changes in bubble shape and content. The result is a displacement cascade, in which a high-momentum atom collides repeatedly with other atoms, transferring energy to them and producing damage in the crystal. We focus on trajectories that interact with a particular bubble for initial kinetic energies of 10?30 keV. We find that the size and shape of helium bubbles after a cascade can change substantially, depending on how much energy the high-momentum atom imparts to a particular bubble and the tungsten atoms surrounding it. Displacement cascades also locally increase the pressure and change the shapes of bubbles near the surface, causing those bubbles to vent their helium back to the plasma. Future research will sample helium bubbles with different shapes, sizes, and distances from the surface, with the ultimate goal of generating a model of helium transport and dynamics in the divertor that takes neutron effects into account.
Funder Acknowledgement(s): Financial support was provided by the NSF REU program (DMR-1757936).
Faculty Advisor: Karl D. Hammond, firstname.lastname@example.org
Role: For this research project, I utilized a molecular dynamics software called LAMMPS (Large-scale Atomic/Molecular Massively Parallel Simulator), to simulate what would happen to a self-nucleated helium bubble within a tungsten crystal, if a free neutron produced from a deuterium-tritium fusion reaction would collide with a tungsten atom near said helium bubble. My simulation is a continuation from a previous study performed by my adviser and other collaborators, in which the initial configuration of tungsten atoms and helium bubbles in my simulation is a result from the study.