Molecular dynamics simulation of retention and bubble formation in tungsten with carbon impurities under high flux deuterium irradiation

Abstract

W is a critical plasma-facing material in fusion reactors. However, extreme conditions subject W to high-flux D plasma irradiation, resulting in D retention and bubble formation. Importantly, C impurities in the plasma can have a complex effect on D behavior in the W. Due to experimental limitations, the impact of C on the evolution of irradiated W and the underlying mechanisms remains poorly understood. In this study, we employ molecular dynamics simulations to investigate the effects of C on the retention of D in W. The introduction forms of C include irradiation and direct doping. First, Irradiation can cause C to be retained, at the same time, the structure of W is severely damaged. W atoms in the subsurface are bombarded and displaced to form interstitial atoms and even be sputtered out of the W matrix. Statistical results show that the sputtering of W is primarily determined by the energy of impact C, with temperature having relatively minor effects. C irradiation forms a W-C mixed layer on the W surface. This layer has a disordered structure and is mixed with self-interstitial atoms and C atoms. D atoms incident from above are easily intercepted and captured by this layer and are difficult to migrate deeper. Second, C randomly doped in W significantly promotes the retention of D. The higher the C content, the higher the retention rate. Furthermore, the supersaturated accumulation of retained D leads to the formation of D bubbles. D undergoes an evolutionary process of forming molecules, clusters, and finally D bubbles. This work provides new insights into the W-C-D interaction mechanisms in fusion reactors, offering important theoretical support for the selection of W as a plasma-facing material.