Microscopic mechanism of nucleation and growth of helium bubbles in monovacancy in tungsten: helium regulates the charged states of tungsten atoms

Abstract

In fusion reactor, tungsten (W) has been selected as a candidate for plasma-facing materials (PFMs) due to its excellent properties. However, W-PFMs suffer from helium (He) bubbles where He atoms are produced during deuterium tritium fusion in fusion reactors. To date, there have been few contributions to uncovering the formation of He bubbles from the perspective of the microscopic electronic structure of He-mediated tungsten. In this work, we develop a tight-binding potential model for the W-He interaction to study He atom aggregation and nucleation in the electronic ground state as well as in different electronic excited states. The most important finding of this paper is that caused by the He atoms in the vacancy, some d-orbital electrons of the W atoms at the inner wall of the vacancy are transferred to the W atoms farther away from the vacancy, leading to the feature of positively charged W ions at the inner wall of the vacancy. As the number of He atoms in the vacancy increases, these W ions become more cationic. Under the repulsion between these adjacent cationic ions, the volume of vacancies increases, and more He atoms tend to gather and nucleate there. At the same time, the enhancement of the electronic excitation can also promote the abovementioned electron transfer between W atoms and further increase the vacancy volume, which increases the self-aggregation of the He atoms in the vacancy. Our results shed new light on understanding He self-aggregation in many different metal materials.

Electronically Temperature-Dependent Interplay between He and Trivacancy in Tungsten Plasma-Facing Materials

“…In this paper, we utilized our developed W-He TB potential model, which has been presented in detail in our previously published work [28], to calculate our systems of interest. Here, we outline the basic spirit of our computational method as follows.…”

“…Here, we outline the basic spirit of our computational method as follows. In the TB model, the total energy of a system is expressed as the sum of two components [28][29][30]:…”

“…To gain deeper insights into the impact of electronic excitation on the ability of V3 to trap He, we decomposed the trapping energy into three components: band structure energy, repulsive energy, and the energy associated with electron entropy. These components correlate with the electronic structure, atomic structure, and degree of electron disorder distribution within the excited system [28,43]. As illustrated in Figure 3, in the specific scenario where the He atom approaches the V3 defect, the sum of the band structure energy and repulsive energy gradually decreases as the electronic temperature increases.…”

“…This suggests that the predominant factor driving the increase in trapping energy is the enhanced electron disorder distribution resulting from electronic excitation. We also decompose the trapping energy into three components: band structure energy, repulsion energy, and electron entropy [28,43]. As depicted in Figure 10, the sum of the band structure energy and the repulsive energy slightly decreases with increasing electronic temperature.…”

“…In this study, we conducted a thorough investigation into the interaction between He and the most stable V3 configuration in both the electronic ground state and electronically excited states, employing our developed W-He TB potential model [28]. Our TB calculations reveal that the electric dipole interaction between W and He results in the W atom nearest to the He atom on the inner wall of V3 becoming a cation, while the other W atoms on the wall become anions.…”