Molecular dynamics simulation of erosion and surface evolution of tungsten due to bombardment with deuterium and carbon in Tokamak fusion environments

The behavior of tungsten as plasma facing material in fusion environment is investigated using molecular dynamics simulation. Tungsten erosion and surface evolution is simulated during irradiation by carbon and deuterium ions. Non-cumulative pure carbon bombardment on crystal tungsten shows that substrate temperature does not affect carbon trapping rate, implantation depth, and tungsten sputtering yield. Carbon induced tungsten physical sputtering yield threshold is predicted to be around $25 eV. Cumulative carbon irradiation on crystal tungsten reveals that tungsten erosion is enhanced at high substrate temperatures. Cumulative carbon induced tungsten sputtering yield matches experimental data as well as Monte Carlo results. Carbon pre-irradiated tungsten tends to trap more hydrogen and facilitates gas bubble formation. Simultaneous deuterium and carbon bombardment on crystal tungsten indicates that carbon induced tungsten sputtering yield exhibits a maximum value when carbon ratio is around 20%. Higher carbon ratio reduces both the carbon and deuterium trapping rates. Tungsten and carbon fiber composites (CFCs) are plasma-facing components (PFCs) candidates in ITER where they are subjected to high hydrogen plasma fluxes. For carbon-based materials (CBM), chemical interactions with hydrogen isotopes lead to enhanced erosion yield [1], especially at elevated surface temperature ($0.1 at 600–800 K) [2]. Erosion rate of CBM during normal fusion reactor operation is several meters per year [1]. The eroded carbon atoms can migrate to other places and re-deposit on tungsten surface to form thin carbon film and remove tungsten atoms from the surface. The deposited carbon on tungsten surface increases hydrogen retention, which was mainly confined to the carbon-modified layer [3,4], and hydrogen concentration in the carbon deposited layer depends on the incident hydrogen energy: energetic ions lead to hard films with lower hydrogen concentration, while low energy hydrogen leads to soft films with higher hydrogen concentration [5,6]. Computer simulations reveal that hydrogen isotopes bubble could be formed in tungsten carbide, if sufficient high amount of D 2 accumulates in the substrate [7]. The consequences of these complicated processes will result in tungsten dust in the plasma [8]. The dust is formed either directly from erosion process causing ejection of particulates, or by delamination of re-deposited layers. Because tungsten impurities in fusion plasma need to be significantly minimized due to plasma power loss by line radiation from charge states [8], understanding detailed tungsten surface evolution during deuterium bombardment with carbon impurity is crucial for the usage of tungsten and CFCs in fusion reactors. One of the principal …