With the increasing world energy demands, nuclear fusion has attracted a lot of attraction as a potentially clean and sustainable source of energy. The most efficient
nuclear fusion based reactors are based on the magnetic confinement of the plasma in a toroidal shaped chamber called the tokamak. The life-cycle of such reactors is hugely governed by the life-cycle of its component known as the divertor which has the function of extracting heat and acts as an exhaust. The divertor essentially consists of tungsten monoblocks as the plasma facing components, with each monoblock being a tungsten tile bonded to a water-cooled copper alloy heat sink. These tungsten monoblocks are subjected to very high heat and particle (neutrons and ions) loads, where the neutrons result in the generation of point and clustered lattice defects, which further interact with the helium ions. These interactions in combination with high temperature influence the microstructural evolution and ultimately affect the mechanical properties. Thus, an in-depth understanding of the role of helium ions in conjunction with heat and neutron loads is crucial for predicting the microstructure evolution under fusion conditions accurately.
In the present work, a multi-scale model describing the simultaneous effect of the defect generation by neutron irradiation and helium implantation from the plasma is developed. At atomic length scales, the generation of defects such as the vacancies, self-interstitial atoms, their clustering and the trapping of helium at defects and their clusters are modelled using a kinetic rate theory approach. Additionally, these microstructural level interactions are linked to mesoscopic length scales (tungsten monoblock scale) by considering a spatial dependency by diffusion of defects. The spatially varying defect concentrations from the model are also used to obtain a measure of the spatially varying lattice stored energy, thereby allowing to link the effect of helium with mechanisms such as recovery, recrystallization, and grain growth.