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Journal Articles

Spin excitations in optimally P-doped BaFe(As $_{0.7}$ P $_{0.3}$ ) superconductor

Hu, D.*; Yin, Z.*; Zhang, W.*; Ewings, R. A.*; Ikeuchi, Kazuhiko*; Nakamura, Mitsutaka; Roessli, B.*; Wei, Y.*; Zhao, L.*; Chen, G.*; et al.

Physical Review B, 94(9), p.094504_1 - 094504_7, 2016/09

AA2016-0252.pdf:2.18MB

https://doi.org/10.1103/PhysRevB.94.094504

Times Cited Count：16 Percentile：59.36(Materials Science, Multidisciplinary)

The temperature and energy dependence of spin excitations in an optimally P-doped BaFe(As $_{0.7}$ P $_{0.3}$ ) superconductor (T = 30 K) were studied by using inelastic neutron scattering. Experimental results are consistent with calculations from a combined density functional theory and dynamical mean field theory, and suggest that the decreased average pnictogen height in BaFe(As $_{0.7}$ P $_{0.3}$ ) reduces the strength of electron correlations and increases the effective bandwidth of magnetic excitation.

Journal Articles

Overview of plasma-material interaction experiments on EAST employing MAPES

Ding, F.*; Luo, G.-N.*; Pitts, R.*; Litnovsky, A.*; Gong, X.*; Ding, R.*; Mao, H.*; Zhou, H.*; Wampler, W. R.*; Stangeby, P. C.*; et al.

Journal of Nuclear Materials, 455(1-3), p.710 - 716, 2014/12

https://doi.org/10.1016/j.jnucmat.2014.09.017

Times Cited Count：25 Percentile：88.12(Materials Science, Multidisciplinary)

Journal Articles

Nitrate facilitates cadmium uptake, transport and accumulation in the hyperaccumulator

Hu, P.*; Yin, Y.-G.; Ishikawa, Satoru*; Suzui, Nobuo; Kawachi, Naoki; Fujimaki, Shu; Igura, Masato*; Yuan, C.*; Huang, J.*; Li, Z.*; et al.

Environmental Science and Pollution Research, 20(9), p.6306 - 6316, 2013/09

https://doi.org/10.1007/s11356-013-1680-3

Times Cited Count：47 Percentile：77.23(Environmental Sciences)

Journal Articles

Deuterium retention, blistering and local melting at tungsten exposed to high-fluence deuterium plasma

Shu, Wataru; Nakamichi, Masaru; Alimov, V.; Luo, G.-N.*; Isobe, Kanetsugu; Yamanishi, Toshihiko

Journal of Nuclear Materials, 390-391, p.1017 - 1021, 2009/06

https://doi.org/10.1016/j.jnucmat.2009.01.267

Times Cited Count：50 Percentile：95.12(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Mechanisms of retention and blistering in near-surface region of tungsten exposed to high flux deuterium plasmas of tens of eV

Shu, Wataru; Luo, G.; Yamanishi, Toshihiko

Journal of Nuclear Materials, 367-370(2), p.1463 - 1467, 2007/08

https://doi.org/10.1016/j.jnucmat.2007.04.005

Times Cited Count：66 Percentile：96.7(Materials Science, Multidisciplinary)

The mechanisms of retention and blistering in the near-surface region of tungsten exposed to high glux deuterium plasmas of tens of eV were studied with a variety of techniques, such as XRD, TEM, SEM, TDS, NRA and ERDA. The results of small angle XRD at a fixed incident angle of 1.5 $^{circ}$ indicated that within the experimental error there was a zero change in the lattice parameter after the plasma exposure. This implies that deuterium does not exist in the lattice interstitial sites, but instead forms a deuterium-vacancy complex and then clusters and further bubbles (deuterium molecules in vacancy clusters and voids) in near-surface region. Cross-sectional TEM observations showed that small blisters with a diameter of around 30 nm and nano-cracks formed in the near-surface region before the formation of larger blisters with diameters of up to a few microns (comparable to grain size). The TDS results strongly indicated that deuterium existed in the molecular form in tungsten after the plasma exposure. The NRA and ERDA results suggest that the maximum atomic ratio of deuterium against tungsten reached as high as 1-2% in the near-surface region. These evidences suggest that crystal defects like vacancies should be generated due to lowering of the formation energy of vacancies by the intrusion of a great number of hydrogen isotope atoms into the near-surface region of tungsten.

Journal Articles

Microstructure dependence of deuterium retention and blistering in the near-surface region of tungsten exposed to high flux deuterium plasmas of 38 eV at 315 K

Shu, Wataru; Kawasuso, Atsuo; Miwa, Yukio; Wakai, Eiichi; Luo, G.-N.*; Yamanishi, Toshihiko

Physica Scripta, T128, p.96 - 99, 2007/03

https://doi.org/10.1088/0031-8949/2007/T128/019

Times Cited Count：90 Percentile：92.16(Physics, Multidisciplinary)

The dependence of deuterium retention and blistering upon the microstructures of tungsten exposed to 38 eV plasma were studied with TDS, PA and SEM. For samples exposed to higher fluences (up to 10 $^{27}$ D/m $^{-2}$ ), a peculiar phenomenon of bursting release of deuterium was found obviously in TDS spectra, where sudden spikes appeared. SEM observations also confirmed the phenomenon of bursting of blisters, even for the single crystal tungsten (111) exposed to 10 $^{26}$ D/m $^{-2}$ at room temperature. The preliminary PA measurements suggested that the vacancy concentration in the near-surface region of the partially-recrystallized tungsten increased after the exposure, and electron back-scattering diffraction (EBSD) results showed that blisters appeared predominantly on the grains with nearly (111) surface orientation.

Journal Articles

Influence of blistering on deuterium retention in tungsten irradiated by high flux deuterium 10-100eV plasmas

Luo, G.; Shu, Wataru; Nishi, Masataka

Fusion Engineering and Design, 81(8-14), p.957 - 962, 2006/02

https://doi.org/10.1016/j.fusengdes.2005.09.023

Times Cited Count：66 Percentile：96.73(Nuclear Science & Technology)

The influence of blistering on deuterium retention in W was investigated using the newly established plasma generator with controllable incident energies ranging from 100 eV down to around 10 eV and incident flux of 110 $^{22}$ D/m $^{2}$ /s. The retention in the irradiated samples was measured using a thermal desorption spectrometer (TDS) at a ramping rate of 5 $^{circ}$ C/s. The results indicate that only one peak appears in each spectrum, with the peak temperatures ranging from 500 until 850 $^{circ}$ C, much higher than those from the trapping sites like vacancies, grain boundaries, dislocation loops, or impurities, implying probably a direct origin from the molecules existing inside blisters, voids/bubbles. Significant decrease in the retention at a certain incident fluence after blister appearance was observed and attributed to rupturing of the blisters, consistent with the limited size and increasing number of the blisters with increasing the incident fluence, as observed by means of SEM.

Journal Articles

Incident energy dependence of blistering at tungsten irradiated by low energy high flux deuterium plasma beams

Luo, G.; Shu, Wataru; Nishi, Masataka

Journal of Nuclear Materials, 347(1-2), p.111 - 117, 2005/12

https://doi.org/10.1016/j.jnucmat.2005.07.014

Times Cited Count：84 Percentile：98.12(Materials Science, Multidisciplinary)

Polycrystalline tungsten samples have been irradiated at room temperature by high flux (110 $^{22}$ D/m $^{2}$ /s) deuterium plasma beams with incident energies ranging 7 98 eV/D. Surface blistering occurred at all energies. The critical fluence for blistering $_{cr}$ was found to increase with decreasing the incident energy. At energies 20 eV/D, $_{cr}$ increased more rapidly. This energy dependence of $_{cr}$ may be explained by a proposed model dealing with the oxide barrier to deuterium uptake into and release from the bulk W. At all energies, the blisters increased in their size and number with fluence within the corresponding low fluence ranges. However the size stopped increasing at certain fluences, while the number kept increasing within the experimental fluence range, which could be attributed to rupturing of blisters at a certain size of about 2m.

Journal Articles

Application of Kelvin probe to studies of fusion reactor materials under irradiation

Luo, G.-N.*; Yamaguchi, Kenji; Terai, Takayuki*; Yamawaki, Michio*

Plasma Science and Technology, 7(4), p.2982 - 2984, 2005/08

https://doi.org/10.1088/1009-0630/7/4/026

no abstracts in English

Journal Articles

New conceptual design of a test module assembly for tritium permeation experiment

Ohira, Shigeru; Luo, G.; Nakamura, Hirofumi; Shu, Wataru; Kitamura, Kazunori*; Nishi, Masataka

Fusion Science and Technology, 48(1), p.621 - 624, 2005/07

https://doi.org/10.13182/FST05-A1002

Times Cited Count：0 Percentile：0.01(Nuclear Science & Technology)

A new conceptual design of a tritium permeation test module assembly was developed for demonstration tests using a strong plasma source constructed in TPL for simulation of practical tritium permeation in the real plasma facing components and validation of the models and codes for evaluation of tritium permeation. The target module, to be irradiated by the high flux plasma beam, consists of a multi-layer structure of a plasma facing material plate and a copper substrate with pressurized coolant cavity. Tests using a preliminary model of the target module has been performed to verify thermal and mechanical behavior of the bonded structure and to assess its structural integrity focused on the bonded interface under the cyclic heat loads. After the heat load testing, no visible defect and crack was observed around the bonded interfaces with magnifying glass, and its structural integrity was verified. Also the first tests using tritium plasma at TSTA/LANL with the preliminary model was performed and process to measured tritium permeated was established.

Journal Articles

Ion species control in high flux deuterium plasma beams produced by a linear plasma generator

Luo, G.; Shu, Wataru; Nakamura, Hirofumi; Ohira, Shigeru; Nishi, Masataka

Review of Scientific Instruments, 75(11), p.4374 - 4378, 2004/11

https://doi.org/10.1063/1.1807006

Times Cited Count：43 Percentile：85.35(Instruments & Instrumentation)

The ion species ratios in low energy high flux deuterium plasma beams formed in a linear plasma generator were measured by a quadrupole mass spectrometer. And the species control in the plasma generator was evaluated by changing the operational parameters like neutral pressure, arc current, and axial magnetic confinement to the plasma column. The measurements reveal that the lower pressures prefer to form more D $^{+}$ ions, and the medium magnetic confinement at the higher pressures results in production of more D $_{2}$ $^{+}$ , while the stronger confinement and /or larger arc current are helpful to D $_{2}$ $^{+}$ conversion into D $_{3}$ $^{+}$ . Therefore, the ion species can be controlled by adjusting the operational parameters of the plasma generator. With suitable adjustment, we can easily achieve plasma beams highly enriched with a single species of D $^{+}$ , D $_{2}$ $^{+}$ , or D $_{3}$ $^{+}$ , to a ratio over 80%. It has been found that the axial magnetic configuration played a significant role in the formation of D $_{3}$ $^{+}$ within the experimental pressure range.

JAEA Reports

Characteristics of a low energy and high flux compact plasma source and preliminary results in studying surface modification of tungsten irradiated by the source

Luo, G.; Shu, Wataru; Nakamura, Hirofumi; Ohira, Shigeru; Hayashi, Takumi; Nishi, Masataka

JAERI-Tech 2004-031, 27 Pages, 2004/03

JAERI-Tech-2004-031.pdf:2.88MB

A plasma source has been constructed for investigating plasma-surface interactions in a tokamak. It is a compact device with a total length less than 1 m, compared to other existing facilities in the world. However, it can provide with stable plasma beams of low energy (100 eV) and high flux (10 $^{22}$ /m $^{2}$ /s), close to the predicted edge plasma conditions near the ITER divertor. This report presents mainly its configuration and its characteristics, including influence of filament, arc discharge, magnetic field, bias voltage parameters, and so on, on plasma beam being delivered towards the sample. Also shown are the results of preliminary experiments of blister formation on tungsten samples irradiated by a deuterium plasma beam generated with the source.

Journal Articles

Removal of co-deposited layers by excimer lasers

Shu, Wataru; Kawakubo, Yukio*; Luo, G.; Nishi, Masataka

Journal of Nuclear Science and Technology, 40(12), p.1019 - 1026, 2003/12

https://doi.org/10.3327/jnst.40.1019

Times Cited Count：4 Percentile：31.64(Nuclear Science & Technology)

Recovery of tritium from co-deposited layers is a crucial issue for fusion machines that use carbon as plasma facing materials. In this study, the removal rate of the JT-60 and TFTR co-deposited layers by KrF laser was measured for varying laser energy density. The removal rate of 5.0 m/pulse was achieved for the JT-60 co-deposited layers at the energy density of 11 J/cm $^{2}$ for KrF excimer laser. Hydrogen (tritium) was released in the form of hydrogen molecules and readily recovered. The formation of cones due to local surface melting was observed at the KrF laser energy density of 0.8 J/cm $^{2}$ , whereas strong melting was determined to be the mechanism of the ablative removal of the JT-60 co-deposited layers at the energy density greater than the ablation threshold.

Journal Articles

Charging effect on work function measurements of lithium ceramics under irradiation

Luo, G.-N.*; Yamaguchi, Kenji; Terai, Takayuki*; Yamawaki, Michio*

Journal of Alloys and Compounds, 349(1-2), p.211 - 216, 2003/02

https://doi.org/10.1016/S0925-8388(02)00868-X

Times Cited Count：8 Percentile：49.49(Chemistry, Physical)

Lithium ceramics, LiO, LiAlO and LiSiO, under ion or electron beam irradiation have been studied using a Kelvin probe that measures work function changes of materials. Surface charging was observed to influence greatly the probe output, which can be explained qualitatively employing a model concerning polarization effect in insulating ceramics due to free charges on their surfaces. It is found that the insulating ceramics could not be studied properly with the Kelvin probe. A probable solution has been presented, i.e., to heat the ceramics, so as to raise their electric conductivities high enough to root out the surface charges