Simulations of tungsten fuzz growth and erosion under He/Ar mixed plasma irradiation on LP-MIES

Extrinsic noble impurities seeding has been commonly used to reduce the heat flux on divertor target. However, the physical sputtering yield on the target could be obviously enhanced due to larger mass of noble impurities. On the other hand, it has been reported that tungsten fuzz can suppress the physical sputtering due to the trapping effect on sputtered particles. Hence, it is interesting to check the erosion behaviors of tungsten fuzz under the irradiation of noble impurities. Recently, experiments of He/Ar mixed plasma irradiation on W target were conducted on LP-MIES device. Dedicated simulations have been performed by SURO-FUZZ code to study the impact of Ar flux on fuzz growth and erosion, which can well reproduce the experimental measurements on LP-MIES. For the case of pure He incidence, the growth of porous nanostructure leads to an obvious reduction in the fraction of the implanted He particles, which stabilizes to 15 % when the fuzz layer thickness exceeds 1500 nm. For He/Ar mixed plasma irradiation, the dependence of the position of the net sputtering on the local porosity has been investigated in detail. It is found that the net physical sputtering mainly occurs in the regions with the local porosity larger than 0.6.