Effect of ion flux on helium retention in helium-irradiated tungsten

Abstract

Helium retention in irradiated tungsten leads to swelling, pore formation, sample exfoliation and embrittlement with deleterious consequences in many applications. In particular, the use of tungsten in future nuclear fusion plants is proposed due to its good refractory properties. However, serious concerns about tungsten survivability stems from the fact that it must withstand severe irradiation conditions. In magnetic fusion as well as in inertial fusion (particularly with direct drive targets), tungsten components will be exposed to low and high energy ion irradiation (helium), respectively. A common feature is that the most detrimental situations will take place in pulsed mode, i.e., high flux irradiation. There is increasing evidence of a correlation between a high helium flux and an enhancement of detrimental effects on tungsten. Nevertheless, the nature of these effects is not well understood due to the subtleties imposed by the exact temperature profile evolution, ion energy, pulse duration, existence of impurities and simultaneous irradiation with other species. Object Kinetic Monte Carlo is the technique of choice to simulate the evolution of radiation-induced damage inside solids in large temporal and space scales. We have used the recently developed code MMonCa (Modular Monte Carlo simulator), presented at COSIRES 2012 for the first time, to study He retention (and in general defect evolution) in tungsten samples irradiated with high intensity helium pulses. The code simulates the interactions among a large variety of defects and during the irradiation stage and the subsequent annealing steps. The results show that the pulsed mode leads to significantly higher He retention at temperatures higher than 700 K. In this paper we discuss the process of He retention in terms of trap evolution. In addition, we discuss the implications of these findings for inertial fusion.

Temperature dependence of underdense nanostructure formation in tungsten under helium irradiation

“…These results are in very good agreement with the experimentally reported temperature window for fuzz growth (900-2000 K) [17][18][19]. It is noteworthy that our modeling uses a general parameterization for He irradiation in W, which was previously employed to reproduce very different irradiation conditions [31,48,49]. Moreover, in our simulations the mean diameter of HenVm clusters at a fluence of 1.5 × 10 23 m -2 is 0.36 and 0.44 nm at 700 and 900 K, respectively.…”

High temperature indentation of helium-implanted tungsten

“…This conclusion is supported by TEM of helium-implanted tungsten that shows no visible bubbles at He concentrations up to 3000 appm, suggesting the helium is trapped in defects below the resolution limit of the microscope [11]. Finally, DFT modelling of helium in tungsten [24] shows almost complete stability of He n v m clusters (0 r nr 4, 0 rm r4) at temperatures up to $ 400 1C.…”

Resistance to He2+ irradiation damage in metallic glass Fe80Si7.43B12.57

“…For conventional crystalline materials, the strong interaction of irradiation particles with lattice defects may cause displacement damage and microstructure changes [2], and the 14 MeV fusion neutron transmutation helium may cause irradiation damages to the materials, thus affecting the mechanical properties [3]. As to the use of ion beam irradiation for exploring the irradiation resistance of materials [4], the interaction of helium ions with lattice defects is stronger than that of hydrogen ions with lattice defects [5], and helium ions are difficult to dissolve in metal, thus helium bubbles may be formed in the peak helium concentration areas near the surfaces of the materials [6], which play an crucial part in formation of blisters [7] even a separating layer [8].…”