Molecular dynamics simulations were performed in order to investigate the effects of helium upon the displacement cascades in α-iron. Besides conventional analysis tools, a new graphical representation of the data, based upon ternary plots, was introduced. The results showed that the production of defects and their subsequent clustering appeared to be greatly influenced by the presence of helium. Calculations revealed that the location of helium atoms, substitutional or interstitial, played a major role. Compared to pure iron, interstitial helium atoms increased the amount of Frenkel pairs generated during the cascades. Conversely, substitutional helium atoms tend to decrease this production. However, in both cases, it was observed that helium atoms stabilize larger self-interstitial clusters, due to a strong binding energy. These simulations showed that helium atoms trap self-interstitial clusters and would thus slow down their subsequent migration. Some helium–vacancy clusters were generated in the core of the displacement cascades but also grew at the periphery of self-interstitial clusters. It was shown that results greatly depended upon the irradiation temperature. Helium Effects on Displacement Cascades in α-Iron. G.Lucas, R.Schäublin: Journal of Physics - Condensed Matter, 2008, 20[41], 415206 (12pp)