Evaluation of tungsten as divertor plasma-facing material: results from ion irradiation experiments and computer simulations

Abstract

The effect of the primary knock-on atom (PKA) spectrum in radiation damage and the subsequent defect structure formation and their impact in deuterium (D) trapping has been investigated using computer simulations and surrogate ion irradiation experiments. The neutron spectrum for an 'ITER-like' divertor shape and parameters has been generated using ATTILA and SPECTER codes to identify the relevant PKA energies. It has been observed that 10 MeV boron (B) produces a PKA spectrum similar to that obtained from a reactor-like neutron spectrum. Experiments have been carried out with ions of gold (Au), B, helium (He) and D with energies ranging from 0.1 MeV-80 MeV for a fluence range of 1.3 × 10 18 ions m −2 -5 × 10 21 ions m −2 , and distinctly different PKA spectra have been produced. While 80 MeV Au ions produced dense and small clusters of interstitial defects (<10 nm), B produced large dislocation loops up to 60 nm in size. At room temperature, the imprint of the cascade is well captured by the vacancies due to their low mobility, and the vacancy defects observed in Au and B irradiation showed significant differences. Molecular dynamics simulations show that at PKA energies exceeding 150 keV, the fragmentation of the cascades takes place, which tends to limit the size of individual defects in the case of 80 MeV Au irradiation. A mechanism based on the competitive capture of mobile interstitials has been proposed to explain the observed large dislocation loops as well as dislocation lines in different irradiation experiments.

Studies on the role of ion mass and energy in the defect production in irradiation experiments in tungsten

“…It was also reported that in high-energy ion irradiation with ions of mass 28 (Si) or above similar deuterium trapping in W was observed [15]. In a previous study we have also shown the similarities in the defect size distribution due to heavy ion irradiation at room temperature and fission neutrons at high temperature using transmission electron microscopy (TEM) analysis [16].…”

“…TEM analysis of the samples has also shown extensive dislocation formation in the Au-and B-irradiated samples. We observed dislocation lines, loops and clusters in the BLF, BHF and Au-irradiated samples [16,19]. We found dislocations of edge, screw and mixed types with the majority being the mixed type (66%) in Au-irradiated samples and of the screw type in B-irradiated samples (44%).…”

“…The first set was annealed at 1838 K for about 50 min in a vacuum furnace at a base pressure of 0.1 Pa. The annealing was carried out in an inert environment of 10 4 Pa Ar + 8% H 2 gas to prevent the surface oxidation of W at high temperature [16]. These samples are referred to as 'RC1'.…”

“…To understand this, we have deconvolved the timing spectra in two methods by assuming that the characteristic lifetime of the samples does not alter after irradiation (τ 1 = 108.5 ps). In the first case the τ 1 was fixed at 108.5 ps without fixing its intensity and the resultant τ 2 values are 221.8 ps, 209.8 ps and 231 ps for BLF, BHF and Auirradiated samples, respectively [16]. The intensities of these components were 50%, 45% and 35%, respectively.…”

Interplay between the Edge Dislocation and Hydrogen in Tungsten at Electronically Excited States

“…[1] Although W-PFM has the advantages of good thermodynamic properties and a low physical sputtering rate, its safe service in the extreme environment of the fusion reactor is still a challenge. In a fusion reactor, the W-PFM DOI: 10.1002/apxr.202200115 is exposed to irradiation from the plasma, including hydrogen (H) isotope irradiation, which creates defects such as vacancies, dislocations, grain boundaries, and H bubbles, [2][3][4][5][6][7] etc. Among these defects, the formation and evolution of H bubbles have received much attention.…”