Spatially dependent cluster dynamics modeling of microstructure evolution in low energy helium irradiated tungsten

Abstract

In fusion reactors, plasma facing components (PFC) and in particular the divertor will be irradiated with high fluxes of low energy (∼100 eV) helium and hydrogen ions. Tungsten is one of the leading candidate divertor materials for ITER and DEMO fusion reactors. However, the behavior of tungsten under high dose, coupled helium/hydrogen exposure remains to be fully understood. The PFC response and performance changes are intimately related to microstructural changes, such as the formation of point defect clusters, helium and hydrogen bubbles or dislocation loops. Computational materials modeling has been used to investigate the mechanisms controlling microstructural evolution in tungsten following high dose, high temperature helium exposure. The aim of this study is to understand and predict helium implantation, primary defect production and defect diffusion, helium-defect clustering and interactions below a tungsten surface exposed to low energy helium irradiation. The important defects include interstitial clusters, vacancy clusters, helium interstitials and helium-vacancy clusters. We report results from a one-dimensional, spatially dependent cluster dynamics model based on the continuum reaction–diffusion rate theory to describe the evolution in space and time of all these defects. The key parameter inputs to the model (diffusion coefficients, migration and binding energies, initial defect production) are determined from a combination of atomistic materials modeling and available experimental data.

Irradiation hardening of pure tungsten exposed to neutron irradiation

“…In addition, voids were observed in tungsten samples irradiated in the temperature range from 724 to 800°C, covering the dose levels of 0.15 to 2.2 dpa. Since the vacancy migration energy is quite large in tungsten, with reported values ranging from 1.34 to 2.44 eV [15,41] [42], the relatively low vacancy diffusivity will require higher temperatures to induce the interaction of vacancy clusters to promote void nucleation and formation. In addition to the voids and dislocation loops, large W-Re-Os precipitates were also observed in samples irradiated to higher dose levels (>1 dpa) in HFIR, presumably due to the large thermal neutron flux.…”

Temperature dependent surface modification of molybdenum due to low energy He+ ion irradiation

“…Up until now, in the context of plasmas, in nuclear fusion reactors, W is currently considered one of the best options as a PFC material [26,27]. However, the physical mechanism responsible for such deterioration is not very clear yet, although several modeling and simulations viz., molecular dynamic, multiscale and atomistic approaches have also been tried [28][29][30][31][32][33][34][35]. Therefore, studying similar structures on other refractory metal surfaces, such as Mo (as in the present case), is worthwhile which exhibit interesting properties for thermonuclear fusion environments such as resistance to heat, wear and sputtering [36].…”

Grain orientations and grain boundaries in tungsten nonotendril fuzz grown under divertor-like conditions

“…The present understanding of nanostructure formation is primarily informed by molecular dynamics (MD) or other theory approaches [9][10][11][12][13][14][15][16][17][18], with relatively limited (although valuable) experimental information [5,6,8,[19][20][21]. Still poorly defined is how fuzz transitions from the short incipient state of early growth -well-studied by MD -into the long and stably-growing state during later growth.…”