Helium-Ion-Implantation in Tungsten: Progress towards a Coherent Understanding of the Damage Formed and its Effects on Properties

Tungsten is a likely material for divertor armour in fusion reactors. We describe recent progress combining multi-technique experiments with atomistic modelling to understand how injected helium interacts with displacement damage and modifies the physical properties of tungsten. Using X-ray micro-diffraction and laser-induced transient grating measurements, we observe both a lattice swelling and modulus change after helium implantation. Surprisingly, a fraction of a percent lattice expansion is associated with an order of magnitude larger reduction in elastic modulus. These observations are interpreted using a combined elasticity and density functional theory model. We also measure a large reduction of thermal diffusivity due to helium implantation. This can be explained in terms of the underlying damage microstructure using a new atomistic kinetic theory model. Together our observations and calculations allow us to begin to form a joined-up picture of helium-implantation-induced damage in tungsten and its diverse effects on microstructure and physical properties.