Effect of the internal pressure of helium bubbles on the morphology and mobility of beryllium

Abstract

Beryllium (Be) has been selected as the plasma-facing material and a neutron multiplier in ITER. Be is exposed to burning plasma, and helium (He) bubbles are formed and grow. Understanding bubble behavior is crucial because it affects material properties. In this study, the internal pressure and growth behaviors of He bubbles in Be were investigated using in situ transmission electron microscopy (in situ TEM) and scanning transmission electron microscopy combined with electron energy loss spectroscopy (STEM-EELS). It was experimentally examined that the bubble shape, the bubble thickness, and the internal pressure of He bubbles using STEM-EELS. The internal pressure of the spherical He bubbles was higher than that of faceted He bubbles. In situ TEM observation of bubble behaviors under annealing at approximately 973 K showed that the growth rates of spherical He bubbles were higher than those of faceted bubbles. In situ TEM observations indicated that the Brownian motion of the He bubbles depended on their shape. Consequently, the spherical He bubbles with high pressure in Be facilitated bubble growth owing to their high mobility.