National Institutes of Natural Science, National Institute for Fusion Science
Department of Helical Plasma Research, Fundamental Physics Simulation Research Division


The Best Presentation Award at the Joint Conference on Fusion Energy

Assistant Professor Atsushi M. Ito won the Best Presentation Award at the Joint Conference on Fusion Energy.
  • Date: Nov. 30, 2012
  • Title:
    Multi-scale Simulation for Tungsten Nano-structure

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  • Context:
    Helium irradiation onto tungsten surfaces brings about the growth of fuzzy tungsten fibers in the diameter of several ten nano-meter. This material, which is called "tungsten nano-structure", was found by the research on a plasma facing tungsten material in the inside walls of nuclear fusion reactors. Because the incident energy of the helium ions is less than that to sputter the tungsten atoms from the surface, the growth of the fuzzy fibers can be regards as self-organized growth. The formation process of the tungsten nano-structure is not classified into the deposition and processing/etching, which are two kinds of typical processes to create surface nano-structures. The formation mechanisms of tungsten nano-structure have been not well understood. We have grappled with the formation mechanisms of the tungsten-nano structure. The competition of penetration and sputterinf in penetration process was solved by using binary collision approximation. The He agglomeration in the diffusion process was revealed by using density functional theory with the 'OpenMX'[1], and the burst of He bubble in the surface is treated by molecular dynamics. As a result, we explained that He creates bubble but H, Ne, Ar cannot create it with the incident energy of less than 200 eV.