NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
H. Fan, Y. Zhang, D. Liu, C. Niu, L. Liu, W. Ni, Y. Xia, Z. Bi, Günther Benstetter, G. Lei
Tensile stress-driven cracking of W fuzz over W crystal under fusion-relevant He ion irradiations
Nuclear Fusion, vol. 60, no. 4
2020
DOI: 10.1088/1741-4326/ab71bb
Abstract anzeigen
Although W fuzz is formed in the divertor region of the fusion reactor, no theory may clearly explain the W fuzz growth mechanism. In this study, we observe the growth process of W fuzz over W crystal under ITER-relevant He ion irradiations. We propose the tensile stress-driven cracking of nano-structured fuzz during the initial growth of W fuzz. We demonstrate that the existence of tensile stress is due to the swelling of He nano-bubbles in the fuzz. After this cracking, the W fuzz breaks away from the planar network and grows over the W surface, where the micro-stress in the W surface layer acts as the driving force.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
Z. Bi, D. Liu, Y. Zhang, L. Liu, Y. Xia, Y. Hong, H. Fan, Günther Benstetter, G. Lei, L. Yan
The evolution of He nanobubbles in tungsten under fusion-relevant He ion irradiation conditions
Nuclear Fusion, vol. 59, no. 8
2019
DOI: 10.1088/1741-4326/ab2472
Abstract anzeigen
He-induced W nanofuzz growth over the W divertor target is one of the main limiting factors affecting the current design and development of fusion reactors. In this paper, based on He reaction rate model in W, we simulate the growth and evolution of He nanobubbles during W nanofuzz formation under fusion-relevant He+ irradiation conditions. Our modeling unveils the existence of He nanobubble-enriched W surface layer (<10 nm), formed due to the He diffusion in W crystal into defect sites. At an elevated temperature, the growth of He bubbles in the W surface layer prevents He atoms diffusing into the deep layer (>10 nm). The formation of W nanofuzz at the surface is attributed to surface bursting of high-density He bubbles with their radius of ~4 nm, and an increase in the surface area of irradiated W. Our findings have been well confirmed by the experimental measurements.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
L. Liu, S. Li, D. Liu, Günther Benstetter, O. Man, J. Michalicka, Y. Zhang, Y. Hong, H. Fan, W. Ni, Q. Yang, Y. Wu, Z. Bi
The effect of O2 impurity on surface morphology of polycrystalline W during low-energy and high-flux He+ irradiation
Fusion Engineering and Design, vol. 139, pp. 96-103
2019
DOI: 10.1016/j.fusengdes.2019.01.003
Abstract anzeigen
The interaction between the impurities (such as carbon, nitrogen, oxygen) and the plasma-facing materials (PFMs) can profoundly influence the performance and service of the PFMs. In this paper, we investigated the influence of oxygen (O2) impurity in the helium radio frequency (RF) plasma on the surface morphology of polycrystalline tungsten (W) irradiated at the surface temperature of 1450 ± 50 K and the ion energy of 100 eV. The pressure ratio of O2 to He (R) in RF source varied from 4.0 × 10−6 to 9.0 × 10-2. The total irradiation flux and fluence were ˜1.2 × 1022 ions·m-2·s-1 and ˜1.0 × 1026 ions·m-2, respectively. After He+ irradiation, the specimen surface morphology was observed by scanning electron microscopy. It was found that with increasing R from 4.0 × 10−6 to 9.0 × 10-2 the thickness of nano-fuzz layer at the W surface was thinner and thinner, accompanied by the formation of rod-like structures. The erosion yield increased from 5.2 × 10-4 to 2.3 × 10-2 W/ion when R varied from 4.0 × 10-6 to 9.0 × 10-2. The X-ray diffraction analysis shows that tungsten oxides were formed at the near surface of specimens when R exceeded 1.8 × 10-2. The erosion yield measurements revealed that in addition to surface physical sputtering process, the chemical erosion process could occur due to the interaction between oxygen-containing species and W at the surface. The results indicated that the presence of O2 impurity in He plasma can obviously affect the surface microstructure of W. The study suggested that O2 impurity can effectively reduce the growth of nano-fuzz structures.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
L. Liu, S. Li, D. Liu, Günther Benstetter, Y. Zhang, Y. Hong, H. Fan, W. Ni, Q. Yang, Y. Wu, Z. Bi
Surface damages of polycrystalline W and La2O3-doped W induced by high-flux He plasma irradiation
Journal of Nuclear Materials, vol. 501, no. April, pp. 275-281
2018
Abstract anzeigen
In this study, polycrystalline tungsten (W) and three oxide dispersed strengthened W with 0.1 vol %, 1.0 vol % and 5.0 vol % lanthanum trioxide (La2O3) were irradiated with low-energy (200 eV) and high-flux (5.8 × 1021 or 1.4 × 1022 ions/m2⋅s) He+ ions at elevated temperature. After He+ irradiation at a fluence of 3.0 × 1025/m2, their surface damages were observed by scanning electron microscopy, energy dispersive spectroscopy, scanning electron microscopy-electron backscatter diffraction, and conductive atomic force microscopy. Micron-sized holes were formed on the surface of W alloys after He+ irradiation at 1100 K. Analysis shows that the La2O3 grains doped in W were sputtered preferentially by the high-flux He+ ions when compared with the W grains. For irradiation at 1550 K, W nano-fuzz was formed at the surfaces of both polycrystalline W and La2O3-doped W. The thickness of the fuzz layers formed at the surface of La2O3-doped W is 40% lower than the one of polycrystalline W. The presence of La2O3 could suppress the diffusion and coalescence of He atoms inside W, which plays an important role in the growth of nanostructures fuzz.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
L. Liu, D. Liu, Y. Hong, H. Fan, W. Ni, Q. Yang, Z. Bi, Günther Benstetter, S. Li
High-flux He+ irradiation effects on surface damages of tungsten under ITER relevant conditions
Journal of Nuclear Materials, vol. 471, no. April, pp. 1-7
2016
DOI: 10.1016/j.jnucmat.2016.01.001
Abstract anzeigen
A large-power inductively coupled plasma source was designed to perform the continuous helium ions (He+) irradiations of polycrystalline tungsten (W) under International Thermonuclear Experimental Reactor (ITER) relevant conditions. He+ irradiations were performed at He+ fluxes of 2.3 × 1021–1.6 × 1022/m2 s and He+ energies of 12–220 eV. Surface damages and microstructures of irradiated W were observed by scanning electron microscopy. This study showed the growth of nano-fuzzes with their lengths of 1.3–2.0 μm at He+ energies of >70 eV or He+ fluxes of >1.3 × 1022/m2 s. Nanometer-sized defects or columnar microstructures were formed in W surface layer due to low-energy He+ irradiations at an elevated temperature (>1300 K). The diffusion and coalescence of He atoms in W surface layers led to the growth and structures of nano-fuzzes. This study indicated that a reduction of He+ energy below 12–30 eV may greatly decrease the surface damage of tungsten diverter in the fusion reactor.
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