[SY-B8] Symposium B-8

[SY-B8] Kinetic Monte Carlo study of tungsten fuzz formation under low energy helium irradiation

^○Zhangcan Yang, Yingzhao He, Quansong Peng (School of Energy and Power Engineering, Huazhong University of Science and Technology, China)

Tungsten has been considered as the primary candidate for the plasma-facing materials of fusion reactors. However, the formation of fuzz-like nanostructures on tungsten surfaces under low-energy helium plasma irradiation has raised big concerns since these fuzzy structures have been shown to be detrimental to the performance of the materials and the stability of plasma. Unfortunately, the mechanism of fuzz formation is still under debate. Here we present an Object Kinetic Monte Carlo study that links the nucleation and growth of helium bubbles with the evolution of surface morphology. The key difference of our model compared with a previous model by Lasa’s[1] is that the motion of the punched dislocation loops and the diffusion of surface ad-atoms are modeled in detailed in our model. As a result, our model is able to produce real fuzz-like structures rather than the glassy structures in Ref [1]. We first study the sub-surface helium clustering behavior in tungsten as a function of temperature, helium implantation rate, and concentration of pre-existing defects [2]. The key parameters that affect helium clustering behavior have been identified. We then investigate the possible processes that may contribute to the surface evolution and quantitatively analyze their relative contribution. We find that the motion of dislocation loops and the surface diffusion are the two key processes to the surface evolution. Bubble rupture only affects the initial surface roughness, but plays a negligible role in the growth of fuzz structures.
Reference:
[1] A. Lasa et al 2014, EPL, 105(2), 25002.
[2] Z. Yang et al 2017, Fusion Science and Technology, 71(1), 60.