Computational Simulation On The Behavior Of Impurity Atoms And Radiation Defects In Tungsten In Fusion Environment

As the candidate plasma facing material(PFM),tungsten(W)and W-based materials are the most likely to be fully used in fusion devices such as the Experimental and Advanced Superconducting Tokamak(EAST),International Thermonuclear Experimental Reactor(ITER),China Fusion Engineering Test Reactor(CFETR),and DEMOnstration Power Plant(DEMO).During the operation of the fusion reactor,PFMs are irradiated by extremely high temperature H/He plasma and 14 Me V neutrons,causing serious radiation damage.Ne/Ar gases are usually introduced into the fusion device as a coolant,and they also enter the PFMs in the form of impurities and interact with the base material.In addition to radiation damage and impurity atoms,PFMs have to withstand extreme thermal loads and thermal shocks,and complex physical conditions such as temperature gradient fields and stress gradient fields are generated inside them.The evolution of radiation defects in PFMs,as well as the nucleation and release behavior of He/Ne impurities,have a direct impact on the mechanical properties and thermal conductivity of the materials.How to inhibit the accumulation and growth of irradiation defects is one of the key issues in prolonging the service life of fusion reactor materials.Therefore,studying the influence of fusion conditions such as neutron irradiation,temperature gradient field and stress gradient field on the evolution of impurity atoms and irradiation defects can provide theoretical guidance for improving existing PFMs and developing new PFMs,and has important academic significance and application value.In this paper,the interatomic potential functions between W-He/Ne atoms are constructed.On this basis,molecular dynamics simulation is used to study the migration and aggregation behavior of He/Ne impurities in the tungsten bulk.It is found that He/Ne atoms in W can generate large clusters and even bubbles in the W bulk due to the properties of migration,bonding and self-trapping.By further simulations of the growth process of He/Ne bubbles in the near surface of W,it is found that both He/Ne bubbles can induce dislocation loops punching.Comparing the physical characteristics of He/Ne bubble growth,it is found that the pressure threshold of the He bubble punching dislocation loop is lower.Therefore,the lower punching pressure of dislocation loops is considered to be a key factor in the formation of ‘Fuzz’ structures.According to the complex physical conditions in the fusion device,models of temperature gradient field and stress gradient field are established.Molecular dynamic simulations are applied to study the diffusion behavior of typical irradiation defects in temperature gradient field and stress gradient field.The simulation results show that,the migration behavior of interstitial defects in W is characterized by directional movement to the high-temperature region under the temperature gradient,and the temperature gradient field greatly increases the migration rate of interstitial dislocation loops.From the temperature distribution state on the W divertor component in the fusion device,it can be inferred that the interstitial defects in W will rapidly diffuse to the surface of the W bulk,which will cause serious damage to the surface of the W material.The simulation results in the stress gradient field show that the change of stress leads to the change of defect formation energy and migration energy in W,resulting in an energy gradient in the stress gradient field.This energy gradient makes the interstitial defects in W tend to migrate to the stress-concentrated area,and significantly accelerates the migration of dislocation loops.Therefore,the temperature gradient and the stress gradient will cause defects to accumulate in the high temperature area and the stress concentration area of the W material,thereby making the function of the material invalid.In summary,the migration of radiation defects in W will be affected by various factors such as defect types,surface effects,temperature and stress.The temperature gradient field and the stress gradient field have an acceleration effect on defect migration,and cause directional migration of interstitial defects.The accumulation and evolution of typical irradiation defects are important factors for the changes in the mechanical and physical properties of materials.The results reflect the factors affecting the migration of defects in fusion reactor materials,it provide references for methods to inhibit the diffusion and aggregation of defects in the materials,which is of great significance to the development of fusion reactor materials.