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Suche nach „[Y.] [Fan]“ hat 14 Publikationen gefunden
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    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    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.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    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.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    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.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    W. Ni, L. Liu, Y. Zhang, H. Fan, G. Song, D. Liu, Günther Benstetter, G. Lei

    Mass loss of pure W, W-Re alloys, and oxide dispersed W under ITER-relevant He ion irradiations

    Journal of Nuclear Materials, vol. 527

    DOI: 10.1016/j.jnucmat.2019.151800

    Abstract anzeigen

    In this study, polycrystalline W, W-Re alloys, and La2O3 and Y2O3 dispersion-strengthened W have been irradiated by our large-power materials irradiation experimental system (LP-MIES) at the irradiation temperature of 1360–1460 K. Our measurements show that the W nano-fuzz layer which is < 5.2 μm thick has been formed over all the specimens exposed to the low-energy (50 or 100 eV) and high-flux (1.37 × 1022–1.62 × 1022 ions/m2⋅s) He+ irradiations. The mass loss of the fuzz layer almost linearly increases with the He+ fluence, which does not show any dependence on the thickness of fuzz layer varying from 1.1 to 5.2 μm La2O3 and Y2O3 dispersions into W significantly suppress the growth of W fuzz, indicating that He diffusion and the evolution of He nano-bubbles in the near-surface can be significantly influenced due to the dispersion. After He+ (100 eV) irradiation at He+ fluence of 5.83 × 1026/m2, the mass loss of 0.1 vol% - 1.0 vol% La2O3-dispersed W is about 20% lower than the one of the pure W, and the La2O3 dispersed W exhibits the best erosion resistance among various W material grades. Our analysis indicates that both the surface sputtering of W fuzz by energetic ions and surface bursting of He nano-bubbles can be responsible for the mass loss of W under ITER-relevant He+ irradiations.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    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.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Vortrag

    D. Liu, H. Fan, L. Liu, Y. You, Günther Benstetter, F. Zhang

    Surface diffusion and growth of W self-interstitials during low-energy and large-flux H/He ion irridiations of polycrystalline W

    International Conference on Plasma Surface Interactions in Controlled Fusion Devices, Princeton University, NJ, USA

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    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.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    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.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    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.

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    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

    DOI: 10.1038/srep10959

    NachhaltigElektrotechnik und MedientechnikIQMA

    Zeitschriftenartikel

    Q. Yang, H. Fan, W. Ni, L. Liu, Tobias Berthold, Günther Benstetter, D. Liu, Y. Wang

    Observation of interstitial loops in He+ irradiated W by conductive atomic force microscopy

    Acta Materialia, vol. 92, pp. 178-188

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    J. Sun, Y. Fan, Y. Zou, Thomas Stirner, D. Wang

    Investigation of the effects of a thin dielectric layer on low-pressure hydrogen capacitive discharges driven by combined radio frequency and pulse power sources

    Physics of Plasmas, vol. 20, no. 11

    DOI: 10.1063/1.4831775

    Abstract anzeigen

    Negative hydrogen ion sources, for instance for fusion devices, currently attract considerable attention. To generate the precursors—highly rovibrationally excited hydrogen molecules—for negative hydrogen ions effectively by electron excitation, a thin dielectric layer is introduced to cover the surface of the electrically grounded electrode of two parallel metal plates in a low-pressure hydrogen capacitive discharge driven by combined rf and pulse power sources. To understand the characteristics of such discharges, particle-in-cell simulations are conducted to study the effects that the single dielectric layer would bring onto the discharges. The simulation results show that the dielectric layer leads to a much higher plasma density and a much larger production rate of highly vibrationally excited hydrogen molecules compared to discharges without the dielectric layer on the electrode. Further investigation indicates that the nonlinear oscillation of the electrons induced by the nanosecond-pulse continues until it is finally damped down and does not show any dependence on the pulse plateau-time, which is in stark contrast to the case without the dielectric layer present. The physical reason for this phenomenon is explored and explained.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    Y. Fan, Y. Zou, J. Sun, Thomas Stirner, D. Wang

    Study of the effects of a transverse magnetic field on radio frequency argon discharges by two-dimensional particle-in-cell-Monte-Carlo collision simulations

    Physics of Plasmas, vol. 20, no. 10

    DOI: 10.1063/1.4826215

    Abstract anzeigen

    The influence of an applied magnetic field on plasma-related devices has a wide range of applications. Its effects on a plasma have been studied for years; however, there are still many issues that are not understoodwell. This paper reports a detailed kinetic study with thetwo-dimension-in-space and three-dimension-in-velocity particle-in-cellplus Monte Carlo collision method on the role of E×B drift in acapacitive argon discharge, similar to the experiment of You et al.[Thin Solid Films 519, 6981 (2011)]. The parameters chosen in the present study for the external magnetic field are in a range common tomany applications. Two basic configurations of the magnetic field areanalyzed in detail: the magnetic field direction parallel to theelectrode with or without a gradient. With an extensive parametricstudy, we give detailed influences of the drift on the collectivebehaviors of the plasma along a two-dimensional domain, which cannot berepresented by a 1 spatial and 3 velocity dimensions model. By analyzingthe results of the simulations, the occurring collisionless heating mechanism is explained well.

    Hochschulleitung und -einrichtungen

    Beitrag (Sammelband oder Tagungsband)

    Y. Zhao, Peter Sperber, T. Wang, C. Fan, N. Liu, X. Han, Ch. Liu

    Test Report of Clock Distributor in Changchun and Beijing

    Proceedings of the 12th International Workshop on Laser Ranging, Matera, Italien, 16.-20.10.2000