Effect Of The Accumulated Vacancies And Interstitials On The Tungsten Surface On The Surface's Role As Defect Sinks

Neutrons induced displacement damage to the plasma facing material of tungsten will create a large number of point defects,such as self-interstitials atoms(SIAs)and vacancies(Vs).These defects will segregate to the surface and modify the surface morphology in addition to forming immobile defect clusters(Vn/SIAn)in the bulk,such as voids,bubbles and dislocation loops.The defects on the surface not only modify the interaction of the surface with the defects from the bulk,but also inevitably affect the hydrogen/helium behavior near W surfaces.In addition,the displacement damage will further change the surface role as defect sinks of SIAs and Vs.In this work,by combining molecular statics(MS),molecular dynamics(MD)and object kinetic Monte Carlo(OKMC)methods,we study the modification of the tungsten surface morphology and role as defect sinks by clustered vacancies and interstitials on the surface.The thesis is mainly divided into two parts.1.Modification of the tungsten surface morphology by clustered vacancies and interstitials on the surface.By combining molecular statics(MS),molecular dynamics(MD)and object kinetic Monte Carlo(OKMC)methods,we study the clustering of the V/SIA on the two typical low-index W surfaces(1 0 0)and(1 1 0)to uncover the effect of the agglomerated surface V/SIA on the segregation and annihilation of the V and SIA nearby.The study found:(1)MS and MD calculation results show that,Vn/SIAn could form on surfaces(1 0 0)and(110)via the agglomeration of the V/SIA on the two surfaces with the energy release and the reduced energy barrier for the V/SIA diffusion near the Vn/SIAn as respective energetic and kinetic driving force.Yet,the Vn/SIAn is more easily formed on surface(110)compared to surface(1 0 0)due to the much larger binding energy of a V with a Vn(or a SIA with a SIAn)and lower diffusion energy barrier of the V/SIA on surface(1 1 0)than that on surface(1 0 0).Furthermore the Vn on the surface promotes the V segregation energetically.(2)Long-term OKMC simulations at 1000 K show that:under accumulative irradiation,V/SIA clusters are formed on surface(1 1 0),while SIA clusters and point Vs tend to survive on surface(1 0 0).Therefore,surface(1 0 0)could develop to locally convex structures,while surface(1 1 0)will evolve to locally concave-convex structures.2.The effect of the surface Vn/SIAn on the surface's role as a sink for Vs and SIAs are explored.The result shows that,the large Vn on the two surfaces can develop into a locally concave structure that behaves like a locally perfect surface,but the small Vn still remains its character as defects.Meanwhile,we also find that the junction formed between the large Vn and the locally concave surface acts as a deeper sink for the V and SIA than a pure surface;it is energetically and kinetically favorable for the V/SIA near the junction to migrate towards the junction.