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Suche nach „[D.] [Li]“ hat 10 Publikationen gefunden
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    NachhaltigElektrotechnik und Medientechnik

    Zeitschriftenartikel

    J. Michalicka, S. Li, Z. Bi, Y. Zhang, Ondrej Man, Y. Hong, Y. Wu, W. Ni, H. Fan, Günther Benstetter, L. Liu, Q. Yang, D. Liu

    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.

    NachhaltigElektrotechnik und Medientechnik

    Zeitschriftenartikel

    S. Li, Z. Bi, Y. Zhang, D. Liu, Y. Hong, Y. Wu, W. Ni, H. Fan, Günther Benstetter, L. Liu, Q. Yang

    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.

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    E. Bubelis, D. Castelliti, L. Guo, X.-N. Chen, A. Rineiski, M. Schyns, M. Sarotto, Rui Li, F. Gabrielli, L. Andriolo, G. Bandini, F. Belloni

    Safety studies for the MYRRHA critical core with the SIMMER-III code

    Annals of Nuclear Energy, vol. 110, pp. 1030-1042

    2017

    DOI: 10.1016/j.anucene.2017.08.021

    Abstract anzeigen

    The presented studies are carried out within the European 7th framework project MAXSIMA, in which the MYRRHA reactor, which stands for Multi-purpose hYbrid Research Reactor for High-tech Applications, developed at SCK-CEN (Belgian Nuclear Research Centre), is investigated. The SIMMER code is employed for severe accident investigations of the reactor at KIT and SCK-CEN in both critical and ADS subcritical modes. In this paper only studies for the critical core are presented. The SIMMER-III model has been set up and assessed first for the neutronic feedback coefficients. Its calculated fuel, coolant and structure feedbacks agree well with the results evaluated by means of the European Reactor ANalysis Optimized System (ERANOS). For benchmarking of the SIMMER-III coupled neutronics and fluid-dynamics model, several Unprotected Transients due to Over Power (UTOP) have been calculated and compared with results of transient system codes. Very good agreement is demonstrated. In case of the largest and quickest reactivity insertion under hypothetical accident conditions, the reactor is assumed to turn for a short time into a slightly prompt supercritical state, but a quite mild power excursion takes place. Blockage accidents are studied in detail with SIMMER only. In total three scenarios have been investigated, namely the blockages of a single fuel assembly (FA), the protected core blockage scenario and the damage propagation of defective pin failures. Our studies demonstrated no core damage propagation can possibly occur under the different blockage scenarios.

    NachhaltigElektrotechnik und Medientechnik

    Zeitschriftenartikel

    S. Li, Z. Bi, D. Liu, Y. Hong, W. Ni, H. Fan, Günther Benstetter, L. Liu, Q. Yang

    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.

    NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenEuropan Campus Rottal-Inn

    Zeitschriftenartikel

    D. Zhang, E. Merle-Lucotte, X.-N. Chen, A. Rineiski, Rui Li

    Transient analyses for a molten salt fast reactor with optimized core geometry

    Nuclear Engineering and Design, vol. 292, no. October, pp. 164-176

    2015

    DOI: 10.1016/j.nucengdes.2015.06.011

    Abstract anzeigen

    Molten salt reactors (MSRs) have encountered a marked resurgence of interest over the past decades, highlighted by their inclusion as one of the six candidate reactors of the Generation IV advanced nuclear power systems. The present work is carried out in the framework of the European FP-7 project EVOL (Evaluation and Viability Of Liquid fuel fast reactor system). One of the project tasks is to report on safety analyses: calculations of reactor transients using various numerical codes for the molten salt fast reactor (MSFR) under different boundary conditions, assumptions, and for different selected scenarios. Based on the original reference core geometry, an optimized geometry was proposed by Rouch et al. (2014. Ann. Nucl. Energy 64, 449) on thermal-hydraulic design aspects to avoid a recirculation zone near the blanket which accumulates heat and very high temperature exceeding the salt boiling point. Using both fully neutronics thermal-hydraulic coupled codes (SIMMER and COUPLE), we also re-confirm the efforts step by step toward a core geometry without the recirculation zone in particular as concerns the modifications of the core geometrical shape. Different transients namely Unprotected Loss of Heat Sink (ULOHS), Unprotected Loss of Flow (ULOF), Unprotected Transient Over Power (UTOP), Fuel Salt Over Cooling (FSOC) are intensively investigated and discussed with the optimized core geometry. It is demonstrated that due to inherent negative feedbacks, an MSFR plant has a high safety potential.

    Angewandte Naturwissenschaften und Wirtschaftsingenieurwesen

    Zeitschriftenartikel

    L. Li, J. Bai, J. Sun, Thomas Stirner, D. Wang

    Particle simulation of the nonlinear oscillation of electrons induced by a nanosecond pulse in rf capacitive hydrogen discharges

    Physics of Plasmas, vol. 19, no. 3

    2012

    DOI: 10.1063/1.3695121

    Abstract anzeigen

    A particle-in-cell simulation was employed to investigate the nature and physical cause of the nonlinear oscillation of electrons induced by a nanosecond pulse in rf capacitive hydrogen discharges. It was found that the applied nanosecond pulse converted the plasma quickly from the bi-Maxwellian equilibrium formed in the rf capacitive discharge into another temporal bi-Maxwellian equilibrium. When the applied electric field collapses within a few nanoseconds, the electric field arising from the space charge serves as a restoring force to generate a swift oscillation of the electrons. The energy stored in the plasma is converted gradually into the chemical energy during the electron periodic movement. It is also found that the rise-, plateau-, and fall-times of the applied pulse affect the evolution of the electron energy distribution. The collective electron oscillation has a repetition frequency approximately equal to the electron plasma frequency, independent of pulse rise-, plateau-, and fall-times. This oscillation of electrons induced by a nanosecond pulse can be used to generate highly excited vibrational states of hydrogen molecules, which are a necessary precursor for negative hydrogen ions.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

    J. Niu, J. Gu, D. Li, D. Liu, Z. Feng, Günther Benstetter

    Comparison of fluorocarbon film deposition by pulsed/continuous wave and downstream radio frequency plasmas

    Vacuum, vol. 85, no. 2, pp. 253-262

    2010

    Abstract anzeigen

    Fluorocarbon (FC) films have been deposited using pulsed and continuous wave (cw) radio frequency (rf) plasmas fed with hexafluoroethane (C2F6), octafluoropropane (C3F8), or octafluorocyclobutane (C4F8). The effects of feed gases used, discharge pressure, rf power, substrate positions and discharge modes (pulsed or cw) on the deposited films are examined. Film properties are determined using X-ray photoelectron spectroscopy, atomic force microscopy, and static contact angle measurements. The contact angles of FC films are well related to their compositions and structures. Feed gases used, discharge pressure, rf power, substrate positions and discharge modes strongly affect the morphology of the resulting film, as revealed by atomic force microscopy. Optical emission spectrometry measurements were performed to in-situ characterize the gas-phase compositions of the plasmas and radicals’ emission intensities during film deposition. Correlations between film properties, gas-phase plasma diagnostic data, and film growth processes were discussed. The film growth in pulsed or downstream plasmas was controlled by the surface migration of radicals, such as CF2 towards nucleation centers, which result in the deposition of FC films with less cross-linked nature and rougher surfaces. These results demonstrate that it is possible to control film compositions and surface structure by changing deposition parameters.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

    J. Niu, J. Gu, D. Li, Z. Feng, Günther Benstetter, Y. Yin, et al.

    Surface properties of silicon oxide films deposited using low pressure dielectric discharge

    Applied Surface Science, vol. 255, no. 17, pp. 7708-7712

    2009

    Abstract anzeigen

    The deposition of SiOX films from low-pressure dielectric barrier discharge plasmas has been investigated using tetraethoxysilane (TEOS)/O2 as the feed gas. Films were analyzed using X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), AFM-based nanoindentation/nanowear techniques, and conductive AFM. Film deposition rates and hydrocarbon incorporation in the SiOX film decrease with addition of O2. High-quality SiOX films with extremely low surface roughness are deposited at high oxidant concertrations. Addition of oxidant to the feed gas leads to a change in the SiOX film structure from precursor-like to a dense SiOX structure. The SiOX films deposited with TEOS/O2 plasmas were found to have soft surface layers, 0.5–1.5 nm thick, which contribute to an improvement of their field emission properties. The effect of gas phase compositions on the surface properties of the conductive surface layer was discussed.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

    Y. Liu, D. Liu, J. Li, T. Ma, Günther Benstetter

    Properties and deposition processes of a-C: H films from CH4/Ar dielectric barrier discharge plasmas

    Surface & Coatings Technology, vol. 200, no. 20-21, pp. 5819-5822

    2006

    Abstract anzeigen

    Hydrogenated amorphous carbon (a-C: H) films were deposited from CH4+ Ar gas with low-pressure dielectric barrier discharge (DBD) plasmas. The deposition rate, film hardness and surface roughness were examined as a function of Ar concentration in CH4+ Ar. The experimental results revealed that both film hardness and surface roughness increase with increasing Ar concentration from 20% to 67%, and then decrease for Ar concentration exceeding 67%. Also, the deposition rate decreases monotonously with increasing Ar concentration. The high ratio of Ar+ flux per hydrocarbon species for the cases of Ar concentration exceeding 67% leaded to the decrease in growth rate and in surface roughness. CH4+ and Ar+ kinetic energies during the film deposition process were also analyzed theoretically based on ion drift-diffuse model. The theoretical analysis on ion kinetic energy indicated that the deposition of dense a-C: H film is proportional to an increase in kinetic energy of the hydrocarbon ion and the sputter of energetic Ar+ ions.

    Elektrotechnik und Medientechnik

    Zeitschriftenartikel

    Edgar Lodermeier, I. Akula, I. Dudarchyk, D. Li, T. Ma, Y. Liu, Günther Benstetter

    SPM investigation of diamond-like carbon and carbon nitride films

    Surface & Coatings Technology, vol. 172, no. 2-3, pp. 194-203

    2003

    DOI: 10.1016/S0257-8972(03)00338-4

    Abstract anzeigen

    Scanning probe microscopy was used to evaluate and compare the surface roughness, mechanical and tribological properties of hydrogenated (a-C:H) and tetrahedral (ta-C) diamond-like carbon (DLC) and amorphous carbon nitride (a-C:N) films. Compared to the a-C:H and a-C:N films, the ta-C films exhibit the lowest surface roughness. The soft surface layers of DLC and a-C:N films were revealed by nanowear tests and their thickness varies over the range of 0.2 to 4.1 nm. The nanoscale friction coefficient measurements from lateral force microscopy shows that these films have obviously different friction coefficients. The lower friction coefficients of ta-C and a-C:N films can be attributed to the existence of soft graphite-like surface structure. We proposed the deposition processes of DLC and a-C:N films, where their surface roughness, structure and mechanical properties were associated with the vapor plasma particle energy distribution.