Effect of carbon on helium trapping in tungsten: a first-principles investigation

We investigate the effect of carbon (C) on helium (He) trapping in tungsten (W) using a first-principles method. We show C can effectively reduce the solution energy of He in the bulk W originated from the charge density redistribution. This leads to a strong attraction between He and C in W. We demonstrate the C–vacancy (C–V) complex can serve as a trapping center by reducing charge density in its vicinity to induce He nucleation in comparison with the defect-free W. The maximal number of He atoms that can be trapped by such C–V complex is 5, and He diffusion into the C–V complex is kinetically feasible. Further, it is found the binding energy of He to a C–V complex is weaker than that to a C-free vacancy, suggesting C will decrease the He trapping capability of vacancy. We thus propose that C plays a key role in He trapping behavior.