The effect of cascade and helium on microstructural evolution under fusion irradiations

Cascade damage and high helium production rate are major characteristic features of fusion neutron radiation effects. Experimental as well as computational studies of these two factors which have been performed by the authors are presented and discussed from the standpoint of microstructural evolution. The experimental work has been performed using a facility comprising two small ion accelerators and an electron microscope, capable of observing cascade damage during heavy ion bombardment, and of carrying out dual beam irradiations to study the effect of simultaneous injection of helium atoms with displacement cascades. It has been shown that the evolving microstructures depend strongly on the nature of the cascade, type of materials, irradiation temperature, and amount and mode of helium implantation. The implication of these microstructural studies to the radiation effects relevant to fusion reactor design is discussed.