Effect of helium flux on near-surface helium accumulation in plasma-exposed tungsten.

We report results of object kinetic Monte Carlo (OKMC) simulations to understand the effect of helium flux on the near-surface helium accumulation in plasma-facing tungsten, which is initially pristine, defect-free, and has a (100) surface orientation. These OKMC simulations are performed at 933 K for fluxes ranging from 10to 4 × 10He/m s with 100 eV helium atoms impinging on a (100) surface up to a maximum fluence of 4 × 10He/m. In the near-surface region, helium clusters interact elastically with the free surface.

Cascade morphology transition in bcc metals.

Energetic atom collisions in solids induce shockwaves with complex morphologies. In this paper, we establish the existence of a morphological transition in such cascades. The order parameter of the morphology is defined as the exponent, b, in the defect production curve as a function of cascade energy (N(F) ~ E(MD)(b)).

Ab initio study of H, He, Li and Be impurity effect in tungsten Σ3{1 1 2} and Σ27{5 5 2} grain boundaries.

Density functional theory calculations were performed to investigate the effect of H, He, Li and Be impurities on the intergranular cohesion of W Σ3〈1 1 0〉{1 1 2} and Σ27〈1 1 0〉{5 5 2} grain boundaries (GBs). A rigorous search of unique interstices was performed to reveal a range of impurity behaviors. It was found that He exhibits the largest defect formation energy, however it is Li that shows the strongest tendency to segregate towards the GBs.

Multislice simulation of transmission electron microscopy imaging of helium bubbles in Fe.

Formation of nanoscale helium (He) bubbles in reduced activation ferritic/martensitic steels may lead to degradation of mechanical properties of materials. Transmission electron microscopy (TEM) has commonly been used to image the Fresnel contrast of He bubbles, using an underfocus of 0.5-1 µm.