Molecular Dynamics Simulation Of The Displacement Cascades In Tungsten

To date the energy crisis and environment pollution have become more serious, and thedevelopment of nuclear energy is particularly important and urgent. The research anddevelopment of nuclear fusion materials has attracted more attention around the world. Especiallyin fusion reactor, the first-wall material will be exposed in rigorous circumstances, such ashigh-energy neutron intensity radiation for a long-term. Therefore, the performance of the first-wall materials will be one of the key decisions of fusion reactor life. Tungsten is one of the mostpromising candidates for the plasma-facing materials in future nuclear fusion reactors for its highmelting temperature, high thermal conductivity and low sputtering yield. In fusion reactors, thedeposition of helium (He) atoms from fusion plasma and the by-product of (n, α) reactions ofneutrons can both pose He atoms into fusion structural materials at low concentration. Theimplantation and accumulation of He atoms can result in bubble formation and surface blisteringin tungsten and severely degrade the properties of materials. It is, therefore, of great significance toinvestigatetheeffects of interstitialHe atoms on thedisplacement cascades in tungsten.In the present work, the radiation damages in bulk W containing He atoms have been carefullystudied with molecular dynamics (MD) simulations. The effects of He concentration, PKA energyand radiation temperature have been systematically taken into consideration. Based on the NRTmodel and MD simulations, the cascade efficiency has been obtained. It has been found that:(1) inpure W, the radiation temperature will decrease slightly the defects production and cascadeefficiency, but this effect is very weak. Simultaneously, the number of Frenkel pairs increases asthe PKA energy increases.(2) The interstitial He atoms increase the generation of Frenkel pairsand cascade efficiency, and this tendency can be greatly promoted by the concentration ofinterstitial He atoms and irradiation temperature increasing. The defect structures at the final statealso depend strongly on the He concentrations. Many crowdions in the <111> direction have beencaused by the displacement cascades and they can aggregate to form large clusters withpre-existing interstitial He atoms at high concentration.(3) But the case is opposite for thepresence of substitutional He atoms in tungsten. The presence of substitutional He atoms reducethe generation of defects, and this inhibition trends are greatly promoted by the concentration ofsubstitutional Heatoms increasing.