NachhaltigF: Elektrotechnik und MedientechnikZeitschriftenartikel
C. Niu, Y. Zhang, Y. Cui, X. Li, W. Liu, W. Ni, H. Fan, N. Lu, Günther Benstetter, G. Lei, D. Liu
Effect of temperature on the growth and surface bursting of He nano-bubbles in W under fusion-relevant He ion irradiations
Fusion Engineering and Design, vol. 163, no. Available online 26 December 2020
2020
DOI: 10.1016/j.fusengdes.2020.112159
Abstract anzeigen
Under fusion-relevant He+ irradiations, the W surface temperature is one of the most important parameters for controlling the fuzz growth over the W divertor targets, which is associated with the surface bursting of He nano-bubbles. Using He reaction rate model in W, we investigate the effect of temperature on the growth and surface bursting of He nano-bubbles under low-energy (100 eV) and large-flux (∼1022/m2⋅s) He+ irradiations. Increasing the irradiation temperature from 750 to 2500 K leads to a significant change in both the radius of He nano-bubbles and He retention. At an elevated temperature, He solute atoms prefer to rapidly diffuse into He nano-bubbles, thus affecting their concentration, growth and surface bursting. The decrease in He retention is attributed to an increase in the hop rate of solute He atoms in the W top layer, resulting in the significant He release from the W surface. The radius and density of He nano-bubbles calculated by our model are consistent with our experimental observation.
NachhaltigF: Elektrotechnik und MedientechnikZeitschriftenartikel
W. Ni, Y. Zhang, Y. Cui, C. Niu, L. Liu, H. Fan, Günther Benstetter, G. Lei, D. Liu
The effect of fusion-relevant He ion flux on the evolution of He nano-bubbles in W
Plasma Physics and Controlled Fusion, vol. 62, no. 6
2020
DOI: 10.1088/1361-6587/ab8242
Abstract anzeigen
Based on a He reaction rate model in W, we have analyzed the effect of fusion-relevant He+ flux on the evolution and surface bursting of He nano-bubbles in W. The concentrations of solute He atoms, trapped He atoms, and He nano-bubbles, and the radius of He nano-bubbles have been obtained as a function of depth, He+ dose, and He+ flux. He retentions in W are also calculated as the function of He+ dose and flux. Our modeling shows that the He+ flux varying from 5.0 × 1018 to 5.0 × 1024 m−2centerdots−1 significantly affects the concentration of solute He atoms diffusing in W and trapped He atoms, the evolution of He nano-bubbles, and He retention in W. Both the concentration and radius of He nano-bubbles in W show the dependence on He+ flux, and their surface bursting leads to an increase ($\Delta {A_{b - Burst}}$) in the W surface area, thus the growth of W nano-fuzz. When He+ flux increases 5.0 × 1018 to 5.0 × 1024m−2centerdots−1, the bursting rate of He nano-bubbles is greatly reduced, accompanied by an increase in $\Delta {A_{b - Burst}}$. However, $\Delta {A_{b - Burst}}$ is less dependent on the fusion-relevant He+ flux varying from 9.0 × 1020 to 1.6 × 1022m−2centerdots−1, which is consistent with the measured W nano-fuzz growth by He/D2 plasmas.
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
W. Ni, L. Liu, Y. Zhang, C. Niu, H. Fan, G. Song, D. Liu, Günther Benstetter, G. Lei
Effect of intermittent He/D ion irradiations on W nano-fuzz growth over W targets
Vacuum, vol. 173, no. March
2020
DOI: 10.1016/j.vacuum.2019.109146
Abstract anzeigen
The intermittent He/D ion irradiations of polycrystalline W have been performed at the ion energy of 50 eV by changing the time of the single irradiations and the irradiation temperature. All irradiated W specimens have been observed by scanning electron microscopy, and the effect of intermittent He/D ion irradiations on the W fuzz growth has been analyzed. The W fuzz growth over W targets does not show the clear dependence on the intermittent He/D ion irradiations, where the He/D ion fluence of the single irradiations typically varies from 5.0 × 1024 to 2.5 × 1025/m2. However, a slight change in the W surface temperature during the single He ion irradiations significantly affects the W fuzz growth rate. Analysis indicates that W fuzz growth is significantly affected by the total He ion fluence varying from 5.0 × 1024 to 5.0 × 1025/m2 and the irradiation temperature varying from 1100 to 1450 K. This current study will play a crucial role in understanding the W fuzz growth under the periodic He/D ion irradiations of W divertor in fusion reactors, such as ELMs.
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