Effect Of Helium Ion Bombardment Energy On Tungsten Fuzz Growth

The depletion of fossil energy and its pollution to the environment prompt people to develop new energy resources.The fusion energy has gradually entered people's vision.Tokamak is also considered to be the most promising device to achieve fusion energy.Tungsten is used as the major material for divertor targets on ITER due to its high melting point,high thermal conductivity,good thermal stability,low tritium retention,high physical sputtering threshold and no chemical erode.In the fusion facilities,the bombardments of helium(He)plasma on tungsten material will produce nanofibers,also known as tungsten fuzz.The formation of tungsten fuzz not only changes the substrate morphology of tungsten materials,but also changes the properties of metal materials,decreases the thermal conduction of metal,enhances the retention rate of fuel tritium and decreases the optical emission of tungsten materials.Hence,mitigation of the tungsten fuzz while taking advantage of the tungsten targets material is a critical issue.In this paper,the generation and growth of tungsten fuzz under He plasma bombardment are investigated.By upgrading the three-dimensional dynamic Monte Carlo SURO-FUZZ code,the simulation of tungsten fuzz has been successfully conducted in the microns and seconds scales.the time evolution of tungsten fuzz is in good agreement with the existing experimental results.The simulation results show that the temperature of tungsten substrate material directly affects the diffusion of helium ion in the tungsten material.The diffusion coefficient of particles increases with the increase of substrate temperature,resulting in the prosperity of tungsten fuzz.In addition,the helium ion flux of the bombardment to the tungsten material also determines the formation time and length of tungsten fuzz.The growth and sputter of tungsten fuzz are actually dynamic equilibrium processes,and the upgraded SURO-FUZZ code can preliminarily study the effects of high-energy ions exceeding the sputtering threshold of the material on tungsten materials and the comparation with the experimental results is obtained.This thesis consists of the following parts: the background of nuclear fusion,the divertor in Tokamak device,and the formation and influence of fuzz are introduced in section 1.The physical model and process of SURO/SURO-FUZZ code are addressed in section 2.The simulates of the evolution of tungsten materials in the surface morphology with different He ions fluence,flux,energy,substrate temperature with the help of SURO-FUZZ code are studied in section 3.Finally,the main content of this paper is summarized.