Displacement cascades and defects annealing in tungsten, Part I: Defect database from molecular dynamics simulations

Abstract

Molecular dynamics simulations have been used to generate a comprehensive database of surviving defects due to displacement cascades in bulk tungsten. Twenty one data points of primary knock-on atom (PKA) energies ranging from 100 eV (sub-threshold energy) to 100 keV (∼780×E d , where E d is the average displacement threshold energy) have been completed at 300 K, 1025 K and 2050 K. Within this range of PKA energies, two regimes of power-law energy-dependence of the defect production are observed. A distinct power-law exponent characterizes the number of Frenkel pairs produced within each regime. The two regimes intersect at a transition energy which occurs at approximately 250×E d . The transition energy also marks the onset of the formation of large self-interstitial atom (SIAs) clusters (size 14 or more). The observed defect clustering behavior is asymmetric, with SIA clustering increasing with temperature, while the vacancy clustering decreases. This asymmetry increases with temperature such that at 2050 K (∼0.5T m ) practically no large vacancy clusters are formed, meanwhile large SIA clusters appear in all simulations. The implication of such asymmetry on the long-term defect survival and damage accumulation is discussed. In addition, rare <100>{110} SIA loops are observed.

Cascade morphology transition in bcc metals

“…The cascade is initiated by giving a random primary-knock-on-atom (PKA) near the center of the cell an initial velocity with a random direction. In keeping with our comparison to previous work [10][11][12][13], the simulations did not treat electronic stopping. To first order, neglecting electronic losses amounts to an energy shift which is related to the difference between the true PKA energy and the MD cascade energy; the latter of which is essentially equivalent to the damage energy in the Norgett-Robinson-Torrens (NRT) displacement model [11,14].…”

Object kinetic Monte Carlo simulations of irradiated tungsten for nuclear fusion reactors

“…Although the MD results show a higher FP production than in Ref. [142] and a lower FP production than in…”

“…As can be seen in Figure 3.10, the results are similar to those previously published in the literature. Setyawan et al [142] , Troev et al [143] and Caturla et al [144]. Comparing MD results at 300 and 1000 K, it can be observed that the higher the temperature, the higher the recombination rate.…”

“…In those positions, the MD cascades corresponding with the PKA energy were introduced. Setyawan et al [142], Troev et al [143] and Caturla et al [144]. Although the MD results show a higher FP production than in Ref.…”

“…Nevertheless, the difference is low, i.e., the temperature plays a less important role than the PKA energy. At high temperature, the higher defect mobility leads to more recombination, however, vacancies remain practically static in the time scale of the MD simulations [142]. Therefore, no cluster formation is observed with such a low defect density.…”