Fluence Dependence of Surface Morphology and Deuterium Retention in W Bulks and Nanocrystalline W Films Exposed to Deuterium Plasma

Jing Yan,Kaigui Zhu,Xia Li

doi:10.3390/app11041619

Abstract

The surface morphology of pure W bulks and nanocrystalline tungsten films was investigated after exposure to a low-energy (100 eV/D), high-flux (1.8 × 1021 D·m−2s−1) deuterium plasma. Nanocrystalline tungsten films of 6 μm thickness were deposited on tungsten bulks and exposed to deuterium plasma at various fluences ranging from 1.30 × 1025 to 5.18 × 1025 D·m−2. Changes in surface morphology from before to after irradiation were studied with scanning electron microscopy (SEM). The W bulk exposed to low-fluence plasma (1.30 × 1025 D·m−2) shows blisters. The blisters on the W bulk irradiated to higher-fluence plasma are much larger (~2 µm). The blisters on the surface of W films are smaller in size and lower in density than those of the W bulks. In addition, the modifications exhibit the appearance of cracks below the surface after deuterium plasma irradiation. It is suggested that the blisters are caused by the diffusion and aggregation of the deuterium-vacancy clusters. The deuterium retention of the W bulks and nanocrystalline tungsten films was studied using thermal desorption spectroscopy (TDS). The retention of deuterium in W bulks and W films increases with increasing deuterium plasma fluence when irradiated at 500 K.

Highlights

Tungsten (W) is being considered for use as one of the plasma-facing materials (PFMs) in future nuclear fusion devices
The samples are immersed in the high-density deuterium plasma environment, and the deuterium atoms diffuse into W samples [13]
The stress caused by local supersaturation of deuterium causes more deuterium atoms to reach the trap sites and recombine, leading to the establishment of a stress field

Summary

Introduction

Tungsten (W) is being considered for use as one of the plasma-facing materials (PFMs) in future nuclear fusion devices. W is regarded as a favorable PFM due to its high melting point, low erosion rate, high thermal conductivity, etc. As a plasma-facing material, the W surface would be irradiated by magnetically confined plasma, such as helium and hydrogen isotope particles [2]. Hydrogen isotopes would be implanted and retained in the PFM, since this may affect the safe and stable operation of the fusion reactor devices. Changes in surface morphology may result in the degradation of material properties and increase erosion formation. Increased retention has a significant impact on tritium inventory in International Thermonuclear Experimental Reactor (ITER). To estimate the effect of hydrogen isotopes in future fusion reactors, it is necessary to understand the behavior of hydrogen isotopes in plasma-facing materials

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Conclusion