Simulation Of Tungsten Fuzz Formation And Its Impacts On The Angular Distribution Of Eroded Impurities

Tungsten(W)has been widely considered as a major material for the divertor and the first wall in the next-step fusion devices due to is high thermal conductivity and melting point,low sputtering yield and tritium retention.However,the fiber form nanostructure of tungsten surface called “fuzz”,which degrades the performance of tungsten material,has been observed on linear devices,tokamak and stellarator.We developed a three-dimensional(3D)kinetic Monte Carlo(KMC)code SURO-FUZZ to investigate the formation of fuzzy nanostructure in the micro-and seconed-scales.The time evolution of fuzz morphology under helium bombardment is studied by SURO-FUZZ.The growth rate of tungsten fuzz shows a good agreement with the experimental results.Considering this fuzzy surface is rough,in this paper,the impact of surface morphology on the angular distribution of eroded impurity has been investigated with the three-dimensional(3D)rough surface code SURO and a newly developed analytic model.The property of the rough surface structure can be described by the shadow angle of the rough surface in SURO,which is defined as the ratio of the horizontal characteristic length to the initial surface roughness.The SURO simulation results show that the influence of rough surface on the angular distribution of eroded impurity comes into play when the shadow angle is larger than a threshold value.The larger shadow angle of rough surface leads to a stronger shift of the angular distribution of eroded impurity.Different rough surface topographies have been used in the SURO code to check the angular distribution of eroded impurity.It is found that the shift tendency of the angular distribution is similar for different structures of rough surface.Based on the numerical modelling results,an analytical model has been developed to investigate the impact of the shadow angle on the angular distribution of eroded impurity,which shows in the consistent result as the SURO simulations.