Molecular dynamics simulations of cumulative helium bombardments on tungsten surfaces

Low energy and low fluence helium implantations in tungsten: Molecular dynamics simulations and experiments

“…This is due to the different interactions involved in MD and SRIM.The shape of the depth profile obtained with MD simulation is displaying a stratification of the He concentration. Such stratified depth profile was observed by Li et al15 for simulations of 200 eV helium implantation in (001) tungsten at 300 K. They observed a near-surface zone below three or four W layers such as the one we defined as A(fig 7-b)where single helium atoms are located and small clusters formed. They revealed that such small clusters led to changes of the morphology near the substrate surface.…”

“…Both observed formation of growing and exploding clusters which liberate their He content to the surface. In the case of slightly higher energies (300 eV to 1 keV), the mean penetration of the He is observed to be deeper and no "cluster rupture" was identified due to simulations stopped too early in the course of He interactions 15 .…”

“…Henriksson et al studied the behaviour of helium with doses below 10 14 cm -2 and with energies varying from 50 to 200 eV at 0 and 300 K 13 . Li et al investigated implantations of 10 15 cm -2 impinging helium ions on W at 200 eV at temperatures from 300 to 1500 K 14,15 .…”

Theoretical Model of Helium Bubble Growth and Density in Plasma-Facing Metals

“…The pressure in a helium bubble that is far from a surface or grain boundary and which has not yet burst should be greater than or equal to the equilibrium pressure, P eq . As established in prior work [38][39][40][41][42][43][44] , pressure in growing bubbles is relieved by "punching out" dislocation loops, called "loop-punching". The pressure should therefore be less than or approximately equal to the loop-punching stress; as helium is arriving at the bubbles much faster than vacancies are, we expect the pressure inside most bubbles to be closer to the critical value corresponding to loop-punching than to the equilibrium pressure.…”

Estimation of the lifetime of small helium bubbles near tungsten surfaces – A methodological study

“…Atomistic dynamic processes relevant to LEHF irradiation of He on W are plentiful [14], and some of them were addressed by a number of authors based on the molecular dynamics (MD) simulations. For examples, the MD simulations have been performed by Henriksson et al [15], Lasa et al [16] and Li et al [17,18] to study the growth of He bubbles and W surfaces under the cumulative bombardment of He on W surfaces. Because of the limited time scale that is achievable by the MD simulations, the He fluence in these studies was much lower, and the He bubbles were small compared with those in corresponding experiments.…”