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Saito, Shigeru; Suzuki, Kazuhiro; Obata, Hiroki; Dai, Y.*
Nuclear Materials and Energy (Internet), 34, p.101338_1 - 101338_9, 2023/03
Times Cited Count：2 Percentile：53.91(Nuclear Science & Technology)In this study, a post-irradiation examination of pure tungsten (W) and tantalum (Ta) specimens irradiated at the Swiss Spallation-Neutron Source is conducted. W is used as a potential candidate for a solid spallation-target material owing to its favorable properties. However, W also suffers from several disadvantages such as poor corrosion resistance to water coolant and irradiation embrittlement. To improve these properties, cladding technologies using Ta for W alloys have been developed. In the present study, we investigated the irradiation effects on two tungsten materials, poly-crystal W (W-Poly) and single-crystal W (W-Sin), along with pure polycrystalline Ta. The tensile-test results revealed that W-Poly exhibited almost no ductility after irradiation of 10.2-35.0 dpa. W-Sin was irradiated up to 10.2 dpa and demonstrated 6% of total elongation (TE). With regard to Ta, TE decreased based on the increase in irradiation, reaching almost zero at doses of more than 10.3 dpa.
Hirade, Tetsuya; Furuta, Hikaru*; Torikai, Yuji*; Fujimura, Yuki; Michishio, Koji*
JJAP Conference Proceedings (Internet), 9, p.011106_1 - 011106_7, 2023/00
Positron annihilation lifetime (PAL) measurements by use of a positron source of 
Na were performed for polycrystalline ITER-grade tungsten samples exposed to low-energy deuterium plasma. The energy of deuterium plasma was low and then it was expected that it would affect just near-surface region. However, we obtained the longer mean positron annihilation lifetime in the tungsten samples exposed to the low-energy deuterium plasma than the virgin tungsten samples. Moreover, almost same longer values were obtained even on the other (no exposed) side of the samples, although the thickness of the samples were about 2 mm. Although, there has been no report of observation of defect formation by existence of hydrogen or deuterium in tungsten, the results indicated that deuterium existence in tungsten can be one of reasons of defects formation.
Wang, J.*; Hatano, Yuji*; Toyama, Takeshi*; Suzudo, Tomoaki; Hinoki, Tatsuya*; Alimov, V. Kh.*; Schwarz-Selinger, T.*
Journal of Nuclear Materials, 559, p.153449_1 - 153449_7, 2022/02
Times Cited Count：3 Percentile：68.71(Materials Science, Multidisciplinary)To study the effect of the content of chromium (Cr) in the tungsten (W) matrix on the vacancy formation and retention of hydrogen isotopes, the samples of the W-0.3Cr alloy were irradiated with 6.4 MeV Fe ions in the temperature range of 523-1273 K. These displacement-damaged samples were exposed to D
gas at a temperature of 673 K. The addition of 0.3% Cr into the W matrix resulted in a significant decrease in the retention of deuterium compared to pure W after irradiation especially at high temperature. Positron lifetime for W-0.3Cr alloy irradiated at 1073 K was almost similar to that for non-irradiated one. These facts indicate the suppression of the formation of vacancy-type defects by 0.3% Cr addition.
Suzudo, Tomoaki; Tsuru, Tomohito
AIP Advances (Internet), 11(6), p.065012_1 - 065012_7, 2021/06
Times Cited Count：4 Percentile：36.85(Nanoscience & Nanotechnology)In the current study, we analyzed the self-interstitial atoms (SIAs) in BCC molybdenum (Mo) and tungsten (W) in comparison with other BCC transition metals utilizing first-principles method; particularly, we focused on uncommon dumbbells, whose direction are inclined from 
111
toward 110 on the {110} plane. Such a direction is not stable neither in the group 5 BCC metals (i.e., vanadium, niobium, and tantalum) nor in 
-iron. Our first-principles relaxation simulations indicated that inclined dumbbells were more energetically-favored than common 111 dumbbells in Mo, while this is not necessarily the case for W. However, under a certain degree of lattice strain, such as shear or expansive strain, could make inclined dumbbells more favored also in W, suggesting that the lattice strain can substantially influence the migration barrier of SIAs in these metals because inclined dumbbells generally have a larger migration barrier than 111 dumbbells.
Taguchi, Shigeo; Miyauchi, Hironari*; Horigome, Kazushi; Yamamoto, Masahiko; Kuno, Takehiko
Bunseki Kagaku, 67(11), p.681 - 686, 2018/11
In thermal ionization mass spectrometry, de-gassing is one of the important treatments to release impurities of filaments and to minimize the influence of background. In this work, the effect of the surface change in the tungsten filament induced by the conductively heating treatment on uranium isotopic (
U/
U) measurement has been investigated. It was found that the conductively heating treatment of the filament has the effect of smoothing the surface of the filament and also has the effect of improving the deposition of the sample on the filament surface. As a result of either these effects, the precision of uranium isotopic (U/U) measurement was improved.
Suzudo, Tomoaki; Tsuru, Tomohito; Hasegawa, Akira*
Journal of Nuclear Materials, 505, p.15 - 21, 2018/07
Times Cited Count：17 Percentile：86.67(Materials Science, Multidisciplinary)Tungsten (W) is considered as a promising candidate for plasma-facing materials for future nuclear fusion devices, and selecting optimal alloying constituents is a critical issue to improve radiation resistance of the W alloys as well as to improve their mechanical properties. We conducted in the current study a series of first-principles calculations for investigating solvent-solute mixed dumbbells in W crystals. The results suggested that titanium (Ti), vanadium (V), and chromium (Cr) are favorable as solutes for W alloys from irradiation-effect perspectives because these elements are expected to promote vacancy-interstitial recombination without causing radiation-induced precipitation that reduces ductility of irradiated materials.
Marian, J.*; Becquart, C. S.*; Domain, C.*; Dudarev, S. L.*; Gilbert, M. R.*; Kurtz, R. J.*; Mason, D. R.*; Nordlund, K.*; Sand, A. E.*; Snead, L. L.*; et al.
Nuclear Fusion, 57(9), p.092008_1 - 092008_26, 2017/06
Times Cited Count：104 Percentile：99.25(Physics, Fluids & Plasmas)Under the anticipated operating conditions for demonstration magnetic fusion reactors beyond ITER, structural materials will be exposed to unprecedented conditions of irradiation, heat flux, and temperature. While such extreme environments remain inaccessible experimentally, computational modeling and simulation can provide qualitative and quantitative insights into materials response and complement the available experimental measurements. For plasma facing components such as the first wall and the divertor, tungsten (W) has been selected as the best candidate material due to its superior high-temperature and irradiation properties. In this paper we provide a review of recent efforts in computational modeling of W both as a plasma-facing material as well as a bulk structural material subjected to fast neutron irradiation. We highlight several of the most salient findings obtained via computational modeling and point out a number of remaining future challenges.
Suzudo, Tomoaki; Hasegawa, Akira*
Scientific Reports (Internet), 6, p.36738_1 - 36738_6, 2016/11
Times Cited Count：27 Percentile：64.56(Multidisciplinary Sciences)Modeling of the evolution of radiation-induced defects is important for finding radiation-resistant materials, which would be greatly appreciated in nuclear applications. We apply the first principles method combined with kinetic Monte Carlo to indicate a mechanism to mitigate the effect of radiation by adding particular solute elements that change the migration dimension of interstitials in W crystals. The resultant mechanism is applicable to any body-centered-cubic (BCC) metals whose SIAs have one-dimensional (1D) motion and is expected to provide a general guideline for computational design of radiation-resistant alloys in the field of nuclear applications.
Oya, Yasuhisa*; Li, X.*; Sato, Misaki*; Yuyama, Kenta*; Oyaizu, Makoto; Hayashi, Takumi; Yamanishi, Toshihiko; Okuno, Kenji*
Journal of Nuclear Science and Technology, 53(3), p.402 - 405, 2016/03
Times Cited Count：10 Percentile：68.36(Nuclear Science & Technology)The deuterium (D) permeation behaviors for ion damaged tungsten (W) by 3 keV D
and 10 keV C were studied. The D permeability was obtained for un-damaged W at various temperatures. For both D and C implanted W, the permeability was clearly reduced. But, for the D implanted W, the permeability was recovered by heating at 1173 K and it was almost consistent with that for un-damaged W. In the case of C implanted W, the permeability was not recovered even if the sample was heated at 1173 K, indicating that the existence of carbon would prevent the recovery of permeation path in W. In addition, TEM observation showed the voids were grown by heating at 1173 K and not removed, showing the existence of damages would not largely influence on the hydrogen permeation behavior in W in the present study.
Suzudo, Tomoaki; Yamaguchi, Masatake; Hasegawa, Akira*
Journal of Nuclear Materials, 467(Part 1), p.418 - 423, 2015/12
Times Cited Count：45 Percentile：96.77(Materials Science, Multidisciplinary)Tungsten is expected to be a promising plasma-facing material for future fusion devices, but radiation-induced precipitation (RIP), which leads the material to hardening, is a concern at their practical use. One of the keys to accurate prediction of the emergence of RIP is migration of solute atoms, rhenium and osmium, that are produced by nuclear transmutation through irradiation. We conduct a series of numerical simulations using an atomic kinetic Monte Carlo method and investigate the migration of these solute atoms in the form of tungsten-rhenium and tungsten-osmium mixed dumbbells, considered to be the most efficient "carriers" of the solute atoms. We find that the low rotation energy barrier of these mixed dumbbells leading to three-dimensional migration greatly influences their diffusivities. The result also suggests that, although these dumbbells have three-dimensional motion, one cannot simply reduce their migration behavior to that of vacancy-like spherical objects.
Tanigawa, Hiroyasu; Ozawa, Kazumi; Morisada, Yoshiaki*; Noh, S.*; Fujii, Hidetoshi*
Fusion Engineering and Design, 98-99, p.2080 - 2084, 2015/10
Times Cited Count：10 Percentile：64.63(Nuclear Science & Technology)The vacuum plasma spray (VPS) technique has been investigated as the most practical method to form Tungsten (W) layer as a plasma facing material in fusion devices. The issues are the thermal conductivity and the strength of VPS-W, i.e., the thermal conductivity of VPS-W were significantly lower than that of the bulk W, and the hardness of VPS-W is much less than that of the bulk W. These are mainly caused by the porous structure of VPS-W. In order to solve these issues, friction stir processing (FPS) was applied on VPS-W in this study. It was suggested that FSP can contribute to significant improvement both in mechanical and thermal properties of VPS-W coating.
Nakano, Tomohide
Purazuma, Kaku Yugo Gakkai-Shi, 91(3), p.191 - 196, 2015/03
no abstracts in English
films prepared by reactive sputtering depositionYamamoto, Shunya; Hakoda, Teruyuki; Miyashita, Atsumi; Yoshikawa, Masahito
Materials Research Express (Internet), 2(2), p.026401_1 - 026401_8, 2015/02
Times Cited Count：4 Percentile：14.59(Materials Science, Multidisciplinary)The effects of deposition temperature and film thickness on the structural and gasochromic properties of tungsten trioxide films used for the optical detection of diluted cyclohexane have been investigated. The tungsten trioxide films were prepared on SiO substrates by magnetron sputtering, with the deposition temperature ranging from 300 to 550
C in an Ar and O gas mixture. The gasochromic properties of the films, coated with a catalytic Pt layer, were examined by exposing them up to 5% cyclohexane in N gas. We found that (001)-oriented monoclinic tungsten trioxide films, with a columnar structure, grew at deposition temperatures between 400 and 450C. The gasochromic characterization of the tungsten trioxide films revealed that (001)-oriented tungsten trioxide films, with cauliflower-like surface morphology, were appropriate for the optical detection of cyclohexane.
-ion source for the High-Intensity Proton Accelerator (J-PARC)Oguri, Hidetomo; Ueno, Akira; Namekawa, Yuya*; Ikegami, Kiyoshi*
Review of Scientific Instruments, 77(3, Part2), p.03A517_1 - 03A517_3, 2006/03
Times Cited Count：5 Percentile：29.76(Instruments & Instrumentation)The J-PARC Project was started in 2001 as a joint project carried out by JAERI and KEK. At the first stage of the J-PARC, the linac will accelerate the H- ion beam current of 30 mA with a duty factor of 1.25 %. The J-PARC H- ion source driven with a LaB6 filament has regularly delivered more than 35 mA beam with a duty factor of 0.9 % without resorting to cesium. Although the operated duty factor is about 1/3 of the requirement, the filament is not replaced for a half year. At the J-PARC, the lifetime of the tungsten (W) filament was measured by using another H- ion source, which can produce a 72 mA with cesium seeded. The experimental results showed that there is a possibility of the W filament satisfying the lifetime of more than 500 hours, which is J-PARC requirement. We consider the W driven plasma ion source is one of the candidates for the J-PARC source. At present, we are performing the beam test of the cesium free ion source driven with W. We will present the experimental data of the beam test in this conference.
Sato, Satoshi; Verzilov, Y. M.; Ochiai, Kentaro; Nakao, Makoto*; Wada, Masayuki*; Kubota, Naoyoshi; Kondo, Keitaro; Yamauchi, Michinori*; Nishitani, Takeo
Fusion Engineering and Design, 81(8-14), p.1183 - 1193, 2006/02
Times Cited Count：19 Percentile：77.5(Nuclear Science & Technology)no abstracts in English
Tobita, Kenji; Nishio, Satoshi; Enoeda, Mikio; Sato, Masayasu; Isono, Takaaki; Sakurai, Shinji; Nakamura, Hirofumi; Sato, Satoshi; Suzuki, Satoshi; Ando, Masami; et al.
Fusion Engineering and Design, 81(8-14), p.1151 - 1158, 2006/02
Times Cited Count：123 Percentile：99.01(Nuclear Science & Technology)no abstracts in English
Sato, Satoshi; Nakao, Makoto*; Verzilov, Y. M.; Ochiai, Kentaro; Wada, Masayuki*; Kubota, Naoyoshi; Kondo, Keitaro; Yamauchi, Michinori*; Nishitani, Takeo
Nuclear Fusion, 45(7), p.656 - 662, 2005/07
Times Cited Count：8 Percentile：28.14(Physics, Fluids & Plasmas)no abstracts in English
Nasu, Shoichi*; Nagata, Shinji*; Yoshii, Kiichiro*; Takahiro, Katsumi*; Kikuchi, Naoto*; Kusano, Eiji*; Moto, Shintaro*; Yamaguchi, Sadae*; Ohashi, Kentaro*; Noda, Kenji; et al.
Funtai Oyobi Fummatsu Yakin, 52(6), p.427 - 429, 2005/06
no abstracts in English
Sato, Satoshi; Verzilov, Y. M.; Nakao, Makoto*; Ochiai, Kentaro; Wada, Masayuki*; Nishitani, Takeo
Fusion Science and Technology, 47(4), p.1046 - 1051, 2005/05
Times Cited Count：12 Percentile：62.91(Nuclear Science & Technology)no abstracts in English
Oguri, Hidetomo; Namekawa, Yuya*
JAERI-Tech 2004-053, 35 Pages, 2004/07
JAERI-Tech-2004-053.pdf:1.33MB
The high intensity proton accelerator facility project (J-PARC) aims to pursue frontier science in materials science, nuclear physics and nuclear technology, using an accelerator complex at the highest beam power in the world. An H ion source for the project is required to produce a beam current of 60 mA and an emittance of 0.20 
mm.mrad with a duty factor of 2.5 %. In addition, the ion source must be run for 500 h continuously without maintenance. As a result of the beam test, the beam current and the emittance of 72 mA and 0.15 mm.mrad were achieved in the Cs seeded operation, respectively. Because a lifetime of the filament cathode is one of the main restrictions for the maintenance cycle, we started to perform a filament lifetime test. As the result of the test, we succeeded for 258 h arc operation at the arc power of 30 kW with the duty factor of 3 %. Moreover, the results showed that there is a possibility of achievement 800 h lifetime by change the connection between filament and arc power supply and the optimization of the filament shape.
