First-Principles Study on Various Point Defects Formed by Hydrogen and Helium Atoms in Tungsten

Qiang Zhao,Zheng Zhang,Xiaoping Ouyang,Yang Li

doi:10.1155/2017/6547939

Abstract

The different point defects formed by two hydrogen atoms or two helium atoms in tungsten were investigated through first-principles calculation. The energetically favorable site for a hydrogen atom is tetrahedral interstitial site while substitutional site is the most preferred site for a helium atom. The formation energies of two hydrogen or helium atoms are determined by their positions, and they are not simply 2 times the formation energy of a single hydrogen or helium atom’s defect. After relaxation, two adjacent hydrogen atoms are away from each other while helium atoms are close to each other. The reasons for the interaction between two hydrogen or helium atoms are also discussed.

Highlights

Tungsten (W) is widely considered as the most potential plasma facing material (PFM) [1] and the first wall material (FWM) in fusion reactor due to its excellent properties, such as high melting point, high mechanical strength at high temperatures, good thermal conductivity, low thermal expansion coefficient, and high sputtering threshold energy [2]
By using first-principles calculation method based on density functional theory (DFT), we have studied the behavior of hydrogen atoms and helium atoms in body centered cubic (BCC) tungsten
Using first-principles calculation, we studied the BCC W with single and two point defects formed by H or He atoms, respectively

Summary

Introduction

Tungsten (W) is widely considered as the most potential plasma facing material (PFM) [1] and the first wall material (FWM) in fusion reactor due to its excellent properties, such as high melting point, high mechanical strength at high temperatures, good thermal conductivity, low thermal expansion coefficient, and high sputtering threshold energy [2]. Because hydrogen (H) is one of the major plasma background ions, hydrogen irradiation may result in the change of the mechanical properties of tungsten. You presented the experimental results in a divertor plasma simulator NAGDIS-II and observed the formation of hydrogen bubbles on the surface of tungsten [4]. Wang et al studied the behavior of helium on tungsten surfaces and the hydrogen in tungsten by using first-principles calculation [7]. By using first-principles calculation method based on density functional theory (DFT), we have studied the behavior of hydrogen atoms and helium atoms in body centered cubic (BCC) tungsten. Cheng’s research group investigated the blistering behavior and deuterium retention in tungsten exposed to high-flux deuterium-neon mixed plasmas by experiment research [13]. (the temperature of target surface is 10 K) after a lot of first-principles calculations were completed; the results of Nguyen-Manh and Dudarev’s [14] first-principles calculation are in good agreement with experimental data derived from thermal desorption spectroscopy [15] (annealing temperature is about 2150 K)

Models and Computational Details

Results and Discussion

Conclusion