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Plasma facing components for future fusion applications will experience heliumand neutron-induced structural damage. Direct observation of the in-situ dynamic response of such components during particle beam exposure assists in fundamental understanding of the physical phenomena that give rise to their irradiation resistance. We investigated the response of ultrafine and nanocrystalline-grained tungsten to 3 MeV heavy ion irradiations (Si 2+ , Cu 3+ and W 4+) for the simulation of neutron-induced damage through transmutation reactions via in-situ ion irradiation-transmission electron microscopy experiments. Defect densities as a function of irradiation dose (displacement per atom) and fluence were studied. Four stages of defect densities evolution were observed, as a function of irradiation dose: 1) increase in defect density at lower doses 2) higher defect production rate at the intermediate doses (before saturation), 3) reaching the maximum value, and 4) drop of the defect density in the case of W 4+ , possibly due to defect coalescence and grain boundary absorption of small defect clusters. The effect of grain size on defect densities were investigated and found that defect densities were

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The present study reports on high-flux, low-energy He + ion irradiation as a novel method of enhancing the surface porosity and surface area of naturally oxidized niobium (Nb). Our study shows that ion-irradiation-induced Nb surface micro-and nano-structures are highly tunable by varying the target temperature during ion bombardment. Mirrorpolished Nb samples were irradiated with 100 eV He + ions at a flux of 1.2×10 21 ions m-2 s-1 to a total fluence of 4.3×10 24 ions m-2 with simultaneous sample annealing in the temperature range of 773-1223 K to demonstrate the influence of sample temperature on the resulting Nb surface morphology. This surface morphology was primarily characterized using field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Below 923 K, Nb surfaces form nano-scale tendrils and exhibit significant increases in surface porosity. Above 923 K, homogeneously populated nano-pores with an average diameter of ~60 nm are observed in addition to a smaller population of sub-micron sized pores (up to ~230 nm in diameter). Our analysis shows a significant reduction in surface pore number density and surface porosity with increasing sample temperature. High-resolution ex-situ X-ray photoelectron spectroscopy (XPS) shows Nb 2 O 5 phase in all of the ion-irradiated samples. To further demonstrate the length scales in which radiation-induced surface roughening occurs,

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