Surface blistering and deuterium retention in chemical vapor deposition tungsten exposed to deuterium plasma

Abstract

Chemical vapor deposition tungsten (CVD-W) is a promising material for plasma-facing materials. This work evaluated CVD-W samples with a large grain size (CVD-L) and a small grain size (CVD-S) together with rolled W (ND-W) and recrystallized (Rec-W) samples for their performance under deuterium (D) plasma exposure with a flux of 1021 D m−2 s−1 and fluences up to 2 × 1025 D m−2 at a surface temperature of 500 K. Both CVD-L and CVD-S samples featured a columnar grain structure with a preferred orientation close to 〈001〉 || Z, with a more preferred orientation in CVD-L samples. Both CVD-L and CVD-S samples show good resistance to blistering and only few micron-diameter blisters were observed at fluences. In ND-W and Rec-W samples, the number and size of blisters increased with fluence. The D desorption spectra show two desorption peaks in both CVD-W samples at 520 K and 570–604 K. Whereas in ND-W and Rec-W samples, two peaks were at 520 K and 607–700 K. The total D retention in both CVD-L and CVD-S samples was less than 30 % of that in ND-W and Rec-W samples. The low D retention in CVD-W samples was attributed to the low desorption intensities with the peak at 570–604 K. It is suggested that the microstructure of the columnar grain and the 〈001〉 texture in CVD-W samples helps suppressing plasma-induced blistering, therefore reducing D retention. In terms of the stability of the surface integrity and hydrogen isotopes retention, CVD-W demonstrates a significant potential as a wall material for future fusion reactors.

Keywords

• Chemical vapor deposition tungsten
• Deuterium plasma
• Deuterium retention
• Blister