Transmission electron microscopy was performed in situ in order to investigate microstructural changes during low-energy He+ ion bombardment in an electron microscope which was linked to an ion accelerator. The bombardment was carried out using 8 or 0.25keV He+ ions at 293, 873 or 1073K. In the case of 8keV bombardment, irradiation-induced vacancies acted as nucleation sites for dislocation loops and He bubbles. Such defects were formed even at higher temperatures. With increasing bombardment temperature, the growth rates of dislocation loops and He bubbles increased markedly. Although no vacancies were produced during 0.25keV bombardment, He platelets, interstitial loops and He bubbles were formed. Impurity atoms could act as trapping centers for He atoms, which formed bubbles by ejecting W atoms from their lattice sites.

Microstructure Evolution in Tungsten during Low-Energy Helium Ion Irradiation. H.Iwakiri, K.Yasunaga, K.Morishita, N.Yoshida: Journal of Nuclear Materials, 2000, 283-287, 1134-8