Mohamed Abdallah Reza¹, Hongbing Yu¹, Kenichiro Mizohata², Felix Hofmann¹; ¹Department of Engineering Science, University of Oxford, ²Materials Physics, University of Helsinki

Irradiation damage significantly changes the properties of tungsten, the main candidate material for fusion reactor armor. Using transient grating spectroscopy (TGS) we study the reduction of thermal diffusivity in self-ion implanted tungsten from 0.0001 to 10 dpa. Room temperature thermal diffusivity decreases by up to ~55% at 0.1 dpa and saturates thereafter. A kinetic theory model is used to estimate the irradiation-induced point defect density from the measured thermal diffusivity data. This is compared to prior molecular dynamics (MD) simulations and TEM observations of ion-irradiation-induced defects in tungsten. Defects visible in TEM alone cannot account for the measured reduction in thermal diffusivity. However, when point defects predicted by MD but too small to be seen by TEM are accounted for, the defect densities agree well with those estimated from TGS measurements spanning 3 orders of magnitude in dose. This highlights the importance of TEM “invisible” defects for material property evolution.