Evolution of irradiation damage in tungsten matrix and Y2O3 phase after low energy helium plasma exposure

Abstract

Tungsten is the preferred material for the first wall. In this paper, W-0.5 %wt Y2O3 was selected for the exposure test of helium plasma, so that fuzz tendrils of considerable thickness were formed on its surface. By using ultrasonic dispersion, the tendril dispersion was obtained and observed through TEM. The fuzz tendrils on the W matrix surface were seen to have a complete tungsten crystal structure, along with bubbles of different sizes. The outer layer of the tendril is composed of an amorphous material, which is visible on the surface of the fuzz tendril. This is likely due to the subsequent of helium plasma exposure damage. Fuzz tendrils only appeared on the W matrix, whereas Y2O3 particles created nano-protrusions and samll cracks on the surface. The nano-protrusion morphology and EDS analysis, including the lack of Y in fuzz tendrils, indicate that Y2O3 particles were unable to form a fuzzy structure. It is evident that the defects distribution of W matrix and Y2O3 particles is altered due to helium plasma exposure. Near the surface of Y2O3 particles, fewer but larger bubbles were observed, whereas further away, smaller but denser bubbles were seen. In W matrix, bubbles were formed at a deeper level and were larger than the deepest bubbles in Y2O3 particles, likely caused by the lower migration energy. The different responses of W matrix and Y2O3 particles to helium plasma exposure have combined to further reveal the potential of increasing the plasma exposure resistance of plasma-oriented tungsten based materials.