Molecular Dynamics Simulation of Diffusion and Aggregation Behavior of Helium in Tungsten Bulk Materials

Abstract

Controlled thermonuclear fusion is a promising project. If it can be realized, it will certainly replace fossil fuels and solve the problem of energy exhaustion facing humanity. The fusion reaction fuel is a light core, which can be extracted from sea water. The source is very rich, and the fusion reaction of hydrogen and its isotopes is not radioactive, so the fusion energy can be efficient, cheap and clean. At present, the realization of this technology still faces many difficult problems that have not been overcome. The Tokamak device is the most promising device for realizing the controlled thermonuclear fusion. It utilizes a toroidal magnetic field to confine the high temperature plasma. Among them, the choice of plasma-facing materials is the key factor that determines whether or not controlled nuclear fusion can be achieved. For the time being, tungsten is the preferred plasma-facing material. In the case of fusion, tungsten is exposed to extreme conditions such as high temperature and strong radiation, and a large number of defects are generated inside. In this thesis, the molecular dynamics software LAMMPS was used to study one of the defects, interstitial atoms, and the interaction of helium atoms to understand the diffusion and aggregation behavior of helium and the evolution of defects in tungsten. The following aspects are mainly studied: one is the calculation of the binding energy of an interstitial atom and helium atoms, the other is the study of the interstitial and helium atoms’ space configurations, and the third is comparing trap mutation in defective tungsten materials with trap mutation in tungsten materials without defects, and the fourth is the recording of the displacement of the helium atoms and the interstitial atom at temperature control. The study found that the presence of the interstitial atom will indeed affect the aggregation and diffusion of helium atoms, which will trap the movement of helium atoms and cause the helium atoms to gather near the interstitial atoms and form small clusters of helium. As the cluster grows larger, trap mutations occur like a defect-free tungsten block.