Residual stresses in tungsten under exposures with ITER ELM-like plasma loads

Changes in the structure and substructure of tungsten during irradiation by hydrogen plasma flows at the specific energy close to the heat loads on the ITER surface

“…Indeed, as was shown in [7], tensile residual stresses of 600-900 MPa developed in the surface layers of tungsten targets irradiated by sev eral hydrogen plasma pulses. The first experiments showed that the stresses can depend on the plasma flow parameters and decrease with increasing the number of irradiating pulses or the initial sample sur face temperature [7][8][9]. However, the processes that occur at the substructure level and accompany the evolution of internal stresses are still poorly under stood.…”

“…After irradiation by 1-5 hydrogen plasma pulses, the initial macrostresses are annealed and tensile stresses form in the surface layer of the samples, as was noted earlier [7]. The slope of the a sin 2 ψ curves becomes positive.…”

“…The main parameters of the plasma flows were as follows: the particle energy was up to 400 eV, the maximum plasma pressure was 0.32 MPa, and the pulse duration was 0.25 ms. We var ied the heat load on a sample surface (0.15, 0.2, 0.3, 0.45, 0.75 MJ m -2 ), the preliminary heating tempera ture (293, 473, 573, 673, 873 K), and the number of action pulses (up to 150 pulses). The experimental scheme was described in detail in [4,7].…”

“…The full width at half maxi mum of the (400) diffraction maximum is B 400 = (0.36°-0.45°) ± 0.04° and that of the (321) maximum is about 0.3°. For comparison, the samples studied in [7,8] had B 321 = 0.40°-0.49°. These data demonstrate According to an approximation analysis, the coherent scattering region (CSR) in the samples is 60-80 nm and microstrains are almost absent.…”

“…The formation of such macros tresses can be caused by depth nonuniform (gradient) heating of the material [17]. The maximum stresses at 10 irradiation pulses are 350-400 MPa, which are half the stresses measured in [7,9]. An analysis shows that the macrostress increment as compared to the initial state, Δσ = σ irr -σ ini , increases linearly with heat load P and levels off when the melting threshold P > 0.45 MJ m -2 is reached (Fig.…”