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.
I: Zentrum für Akademische WeiterbildungZeitschriftenartikel
A. Al Lily, J. Foland, D. Stoloff, A. Gogus, I. Erguvan, M. Awshar, J. Tondeur, M. Hammond, I. Venter, P. Jerry, A. Oni, Y. Liu, R. Badosek, López de la Madrid, M.C., E. Mazzoni, D. Vlachopoulos, H. Lee, K. Kinley, M. Kalz, U. Sambuu, T. Bushnaq, N. Pinkwart, N. Adedokun-Shittu, P.-O. Zander, K. Oliver, L. Teixeira Pombo, J. Balaban Sali, S. Gregory, S. Tobgay, M. Joy, J. Elen, Odeh Helal Jwaifell, M., M.N.H.M. Said, Y. Al-Saggaf, A. Naaji, J. White, K. Jordan, J. Gerstein, İ. Umit Yapici, C. Sanga, P. Nleya, B. Sbihi, M. Rocha Lucas, V. Mbarika, S. Schön, L. Sujo-Montes, M. Santally, P. Häkkinen, A. Al Saif, Andreas Gegenfurtner, S. Schatz, V. Padilla Vigil, C. Tannahill, S. Padilla Partida, Z. Zhang, K. Charalambous, A. Moreira, M. Coto, et al.
Academic domains as political battlegrounds
A global enquiry by 99 academics in the fields of education and technology
Information Development, vol. 33, no. 3, pp. 270-288
2017
DOI: 10.1177/0266666916646415
Abstract anzeigen
This article theorizes the functional relationship between the human components (i.e., scholars) and non-human components (i.e., structural configurations) of academic domains. It is organized around the following question: in what ways have scholars formed and been formed by the structural configurations of their academic domain? The article uses as a case study the academic domain of education and technology to examine this question. Its authorship approach is innovative, with a worldwide collection of academics (99 authors) collaborating to address the proposed question based on their reflections on daily social and academic practices. This collaboration followed a three-round process of contributions via email. Analysis of these scholars’ reflective accounts was carried out, and a theoretical proposition was established from this analysis. The proposition is of a mutual (yet not necessarily balanced) power (and therefore political) relationship between the human and non-human constituents of an academic realm, with the two shaping one another. One implication of this proposition is that these non-human elements exist as political ‘actors’, just like their human counterparts, having ‘agency’ – which they exercise over humans. This turns academic domains into political (functional or dysfunctional) ‘battlefields’ wherein both humans and non-humans engage in political activities and actions that form the identity of the academic domain.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
H. Fan, Y. You, W. Ni, Q. Yang, L. Liu, Günther Benstetter, D. Liu, C. Liu
Surface degeneration of W crystal irradiated with low-energy hydrogen ions
Scientific Reports (Nature Publishing Group), vol. 6, no. Article number: 23738
2016
DOI: 10.1038/srep23738
Abstract anzeigen
The damage layer of a W (100) crystal irradiated with 120 eV hydrogen ions at a fluence of up to 1.5 × 1025/m2 was investigated by scanning electron microscopy and conductive atomic force microscopy (CAFM). The periodic surface degeneration of the W crystal at a surface temperature of 373 K was formed at increasing hydrogen fluence. Observations by CCD camera and CAFM indicate the existence of ultrathin surface layers due to low-energy H irradiation. The W surface layer can contain a high density of nanometer-sized defects, resulting in the thermal instability of W atoms in the surface layer. Our findings suggest that the periodic surface degeneration of the W crystal can be ascribed to the lateral erosion of W surface layers falling off during the low-energy hydrogen irradiation. Our density functional theory calculations confirm the thermal instability of W atoms in the top layer, especially if H atoms are adsorbed on the surface.
NachhaltigF: Elektrotechnik und MedientechnikI: IQMAZeitschriftenartikel
Q. Yang, Y.-W. You, L. Liu, H. Fan, W. Ni, D. Liu, C. Liu, Günther Benstetter, Y. Wang
Nanostructured fuzz growth on tungsten under low-energy and high-flux He irradiation
Scientific Reports (Nature Publishing Group), vol. 5, no. Article number: 10959, pp. 1-9
2015
DOI: 10.1038/srep10959
NachhaltigF: Angewandte Naturwissenschaften und WirtschaftsingenieurwesenZeitschriftenartikel
S. Liu, S. Dai, C. Sang, J. Sun, Thomas Stirner, D. Wang
Molecular dynamics simulation of the formation, growth and bursting of bubbles in tungsten exposed to high fluxes of low energy deuterium
Journal of Nuclear Materials - PLASMA-SURFACE INTERACTIONS 21 — Proceedings of the 21st International Conference on Plasma-Surface Interactions in Controlled Fusion Devices Kanazawa, Japan, May 26-30, 2014, vol. 463, no. August, pp. 363-366
2015
DOI: 10.1016/j.jnucmat.2014.12.060
Abstract anzeigen
Molecular dynamics simulations are carried out to investigate the formation, growth and bursting of bubbles in tungsten exposed to the irradiation of an extremely high deuterium flux. It is found that the bubbles form in the region near the location of the implanted ion distribution peaks, and that the effect of the substrate temperature on the bubble formation depth is negligible; it is also found that the percentage of deuterium that is found in D2 molecules increases as the bubble grows, and that the evolution of the bubble’s internal pressure is strongly associated with the properties of its surrounding structure. The simulations display the development of a dome-shaped structure at the tungsten surface during the bubble growth. The merging of two deuterium bubbles is also observed. The present simulations also show that the bubble bursts by generating a partially opened lid, which has already been observed in previous independent experiments.
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