In-situ TEM investigation of 30 keV he+ irradiated tungsten: Effects of temperature, fluence, and sample thickness on dislocation loop evolution

In-situ irradiations with 30 keV He+ were performed on tungsten in an investigation of the influences of irradiation temperature and fluence, pre-existing dislocation and sample thickness on dislocation loop evolution including interaction, density and size. Dislocation loops with b = 1/2<111> and b =<100> were found to form in tungsten during irradiation. The ratio of 〈100〉 loops was obviously affected by irradiation temperature, fluence, sample thickness and pre-existing dislocation lines. The interaction between high density helium clusters could stimulate the formation of 〈100〉 loops in irradiated W, which was verified by Molecular Dynamic (MD) simulations. In addition, the driving force for the 〈100〉 loop formation should also be attributed to the reaction of two 1/2<111> loop variants driven by long-time and elevated temperature irradiation. The pre-existing dislocation lines were found to have a profound effect on the size, density and Burgers vector of dislocation loops. Additionally, irradiation-induced defects were likely to be absorbed by the surface sinks of thin foil during ion irradiation, resulting in the formation of a denuded zone near the surface. The in-situ observation of irradiation defect evolution will lead to an improved fundamental understanding of irradiation damage process of tungsten serviced in fusion reactor.