Molecular dynamics simulations reveal sub-surface mechanisms likely involved in the initial formation of nanometre-sized ‘fuzz’ in tungsten exposed to low-energy helium plasmas. Helium clusters grow to over-pressurized bubbles as a result of repeated cycles of helium absorption and Frenkel pair formation. The self-interstitials either reach the surface as isolated adatoms or trap at the bubble periphery before organizing into prismatic 〈1 1 1〉 dislocation loops. Surface roughening occurs as single adatoms migrate to the surface, prismatic loops glide to the surface to form adatom islands, and ultimately as over-pressurized gas bubbles burst.

A reactive interatomic potential based on an analytic bond-order scheme is developed for the ternary system W-C-H. The model combines Brenner's hydrocarbon potential with parameter sets for W-W, W-C and W-H interactions and is adjusted to materials properties of reference structures with different local atomic coordinations including tungsten carbide, W-H molecules as well as H dissolved in bulk W. The potential has been tested in various scenarios, like surface, defect, and melting properties, none of which were considered in the fitting. The intended area of application is simulations of hydrogen and hydrocarbon interactions with tungsten, that have a crucial role in fusion reactor plasma-walls. Furthermore, this study shows that the angular dependent bond-order scheme can be extended to second-nearest neighbor interactions, which are relevant in body-centered cubic metals. Moreover, it provides a possibly general route for modeling metal carbides.

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A reactive interatomic bond-order potential for bcc tungsten is presented. Special attention in the potential development was given for obtaining accurate formation and migration energies for point defects, making the potential useful in atomic scale simulations of point and extended defects. The potential was used to calculate binding energies and trapping distances for vacancies in vacancy clusters and the recombination radius for self-interstitial atom and monovacancy.