Development of Nanostructured Black Metal by Self-Growing Helium Bubbles for Optical Application

2016

JASSE

It is necessary to evaluate the endurance of tungsten (W) under plasma irradiation to realize the nuclear fusion reactor. The tungsten that has flat surface and amorphous structure is often assumed in the experiment and the simulation in plasma-wall-interaction study. However, from experiments, it has been reported that the sputtering yield for the flat surface W under argon (Ar) irradiation is different from that for the rough (fuzz) surface W. In our previous work, using binary-collision-approximation (BCA) simulation, we calculated the sputtering yield under Ar irradiation onto W target which has "simplified rough surface." We could obtain the roughness dependence of the sputtering yield, which is coincident qualitatively with the experimental result. In this paper, we also calculated the physical quantities, i.e., sputtering yield, retention rate and mean penetration depth, under the noble (helium, neon, or argon) gas irradiation onto four types of the flat W targets: Amorphous W and BCC W lattices with the crystal orientation (110), (100) and (111). This simulation shows that the W surface structure affects noticeably the physical quantities. From these simulations, we propose that it is necessary to consider the surface form and the crystal structure to evaluate the sputtering phenomena though it has not been considered sufficiently.

Section: Introductionmentioning

confidence: 99%

Sputtering Yield of Noble Gas Irradiation onto Tungsten Surface

Nakamura

Saitô

2016

JASSE

“…The diffusion and aggregation of vacancies cause embrittlement. Moreover, the diffusion of vacancies in tungsten materials is effective against the formation of helium bubbles [1] and tungsten fuzzy nanostructures [2]. Fuzzy nano-structures cause embrittlement in the divertor materials, which subsequently embrittlement causes the release of impurities in the vessel.…”

Section: Introductionmentioning

confidence: 99%

First-Principles Study on Migration of Vacancy in Tungsten

Oda

Plasma and Fusion Research

Takayama

et al. 2014

We calculated the binding and migration energies of mono-vacancies and di-vacancies in tungsten material using density functional theory. Mono-vacancies diffuse in the [111] direction easier than in the [001] direction. The migration energies of mono-vacancies and di-vacancies are almost the same; moreover, the migration of mono-vacancies and di-vacancies is nearly similar. The di-vacancy binding energies are almost zero or negative. The interactions between two vacancies in tungsten material are repulsive from the second to the fifth nearest neighbors. The vacancies are difficult to aggregate because di-vacancies are less stable than mono-vacancies.

“…Tungsten nanostructure [1][2][3][4][5][6] is a phenomenon that has attracted attention in fusion science. Under helium plasma irradiation, a "bubble" structure is formed around the surface of tungsten [1,2].…”

Section: Introductionmentioning

confidence: 99%

“…Under helium plasma irradiation, a "bubble" structure is formed around the surface of tungsten [1,2]. For the special case when the tungsten temperature is 1000 -2000 K and the incident energy of the helium plasma is 20 -100 eV, a nanofilament structure, called a "fuzz" structure, is generated on the tungsten surface [3,4]. To explain these experimental results, theories [7][8][9] of the formation of the fuzz structure have been proposed.…”

Section: Introductionmentioning

confidence: 99%

Tungsten-Surface-Structure Dependence of Sputtering Yield for a Noble Gas

Nakamura

Saitô

Plasma and Fusion Research

et al. 2016

Using the binary-collision approximation simulation with atomic collision in any structured target code AC∀T, we calculated sputtering yield, range, and retention rate for tungsten with a rough surface under argon atom irradiation. The simulation revealed the sputtering yield decreases and the retention rate increases as the surface becomes rougher. Because these quantities strongly depend on the surface, we suggest that it is necessary to consider the surface structure of the tungsten target when estimating the effects of walls.