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Journal Articles

Determination of fusion barrier distributions from quasielastic scattering cross sections towards superheavy nuclei synthesis

Tanaka, Taiki*; Narikiyo, Yoshihiro*; Morita, Kosuke*; Fujita, Kunihiro*; Kaji, Daiya*; Morimoto, Koji*; Yamaki, Sayaka*; Wakabayashi, Yasuo*; Tanaka, Kengo*; Takeyama, Mirei*; et al.

Journal of the Physical Society of Japan, 87(1), p.014201_1 - 014201_9, 2018/01

 Times Cited Count:10 Percentile:68.3(Physics, Multidisciplinary)

Excitation functions of quasielastic scattering cross sections for the $$^{48}$$Ca + $$^{208}$$Pb, $$^{50}$$Ti + $$^{208}$$Pb, and $$^{48}$$Ca + $$^{248}$$Cm reactions were successfully measured by using the gas-filled recoil-ion separator GARIS. Fusion barrier distributions were extracted from these data, and compared with the coupled-channels calculations. It was found that the peak energies of the barrier distributions for the $$^{48}$$Ca + $$^{208}$$Pb and $$^{50}$$Ti + $$^{208}$$Pb systems coincide with those of the 2n evaporation channel cross sections for the systems, while that of the $$^{48}$$Ca + $$^{248}$$Cm is located slightly below the 4n evaporation ones. This results provide us helpful information to predict the optimum beam energy to synthesize superheavy nuclei.

Journal Articles

Spin resonance in the new-structure-type iron-based superconductor CaKFe$$_{4}$$As$$_{4}$$

Iida, Kazuki*; Ishikado, Motoyuki*; Nagai, Yuki; Yoshida, Hiroyuki*; Christianson, A. D.*; Murai, Naoki; Kawashima, Kenji*; Yoshida, Yoshiyuki*; Eisaki, Hiroshi*; Iyo, Akira*

Journal of the Physical Society of Japan, 86(9), p.093703_1 - 093703_4, 2017/09

 Times Cited Count:22 Percentile:83.13(Physics, Multidisciplinary)

Journal Articles

Welding technology on sector assembly of the JT-60SA vacuum vessel

Shibama, Yusuke; Okano, Fuminori; Yagyu, Junichi; Kaminaga, Atsushi; Miyo, Yasuhiko; Hayakawa, Atsuro*; Sagawa, Keiich*; Mochida, Tsutomu*; Morimoto, Tamotsu*; Hamada, Takashi*; et al.

Fusion Engineering and Design, 98-99, p.1614 - 1619, 2015/10

 Times Cited Count:3 Percentile:30.02(Nuclear Science & Technology)

The JT-60SA vacuum vessel (150 tons) is a double wall torus structure and the maximum major radius of 5.0 m and height of 6.6 m. The manufacturing design concept is that the vessel is split in the 10 toroidal sectors manufactured at factory, and assembled on-site; seven of the 40-degree sectors, two of the 30-degree beside final one, and the final of the 20-degree. The final sector is assembled with the VV thermal shield and toroidal field magnets into the 340-degree as prepared in one sector. Sectors are temporally fitted on-site and adjusted one over the other before the assembly. After measurement of the dimensions and the reference, these sectors are transferred onto the cryostat base. First, three 80-degree sectors are manufactured with mating each 40-degree sector by direct joint welding. The rest sectors including the final sector are jointed with splice plates. Welding manipulator and its guide rails are used for these welding. In this paper, the detail of the VV sectors assembly including the final sector is explained. Welding technologies to joint the two of 40-degree sectors are reported with the present manufacturing status and the welding trial on the vertical stub with the partial mock-up of the final sector are discussed with the assembly process.

Journal Articles

Dismantlement of large fusion experimental device JT-60U

Ikeda, Yoshitaka; Okano, Fuminori; Sakasai, Akira; Hanada, Masaya; Akino, Noboru; Ichige, Hisashi; Kaminaga, Atsushi; Kiyono, Kimihiro; Kubo, Hirotaka; Kobayashi, Kazuhiro; et al.

Nihon Genshiryoku Gakkai Wabun Rombunshi, 13(4), p.167 - 178, 2014/12

The JT-60U torus was disassembled so as to newly install the superconducting tokamak JT-60SA torus. The JT-60U used the deuterium for 18 years, so the disassembly project of the JT-60U was the first disassembly experience of a fusion device with radioactivation in Japan. All disassembly components were stored with recording the data such as dose rate, weight and kind of material, so as to apply the clearance level regulation in future. The lessons learned from the disassembly project indicated that the cutting technologies and storage management of disassembly components were the key factors to conduct the disassembly project in an efficient way. After completing the disassembly project, efforts have been made to analyze the data for characterizing disassembly activities, so as to contribute the estimation of manpower needs and the radioactivation of the disassembly components on other fusion devices.

Journal Articles

Safe disassembly and storage of radioactive components of JT-60U torus

Ikeda, Yoshitaka; Okano, Fuminori; Hanada, Masaya; Sakasai, Akira; Kubo, Hirotaka; Akino, Noboru; Chiba, Shinichi; Ichige, Hisashi; Kaminaga, Atsushi; Kiyono, Kimihiro; et al.

Fusion Engineering and Design, 89(9-10), p.2018 - 2023, 2014/10

 Times Cited Count:2 Percentile:18.72(Nuclear Science & Technology)

Disassembly of the JT-60U torus was started in 2009 after 18-years D$$_{2}$$ operations, and was completed in October 2012. The JT-60U torus was featured by the complicated and welded structure against the strong electromagnetic force, and by the radioactivation due to D-D reactions. Since this work is the first experience of disassembling a large radioactive fusion device in Japan, careful disassembly activities have been made. About 13,000 components cut into pieces with measuring the dose rates were removed from the torus hall and stored safely in storage facilities by using a total wokers of 41,000 person-days during 3 years. The total weight of the disassembly components reached up to 5,400 tons. Most of the disassembly components will be treated as non-radioactive ones after the clearance verification under the Japanese regulation in future. The assembly of JT-60SA has started in January 2013 after this disassembly of JT-60U torus.

Journal Articles

Anisotropic magnetic form factor in a detwinned single crystal of BaFe$$_2$$As$$_2$$

Kodama, Katsuaki; Ishikado, Motoyuki*; Wakimoto, Shuichi; Kiho, Kunihiro*; Lee, C.-H.*; Iyo, Akira*; Eisaki, Hiroshi*; Shamoto, Shinichi

Physical Review B, 90(14), p.144510_1 - 144510_5, 2014/10

 Times Cited Count:1 Percentile:5.23(Materials Science, Multidisciplinary)

JAEA Reports

Storage management of disassembled and radioactive components of JT-60 tokamak device; Storage of radioactive components by containers

Nishiyama, Tomokazu; Miyo, Yasuhiko; Okano, Fuminori; Sasajima, Tadayuki; Ichige, Hisashi; Kaminaga, Atsushi; Miya, Naoyuki; Sukegawa, Atsuhiko; Ikeda, Yoshitaka; Sakasai, Akira

JAEA-Technology 2014-006, 30 Pages, 2014/03

JAEA-Technology-2014-006.pdf:4.87MB

JT-60 tokamak device and the peripheral equipment were disassembled so as to be upgraded to the superconducting tokamak JT-60SA. The disassembled components were stored into storage and airtight containers at the radioactive control area. The total weight and the total number of those components are about 1,100 tons and about 11,500 except for large components. Radiation measurements and records of the radioactive components were required one by one under the law of Act on Prevention of Radiation Disease Due to Radioisotopes, etc. for the control of transport and storage from the radioactive control area to the other area. The storage management of the radioactive components was implemented by establishing the work procedure and the component management system by barcode tags. The radioactive components as many as 11,500 were surely and effectively stored under the law. The report gives the outline of the storage of JT-60 radioactive components by the storage containers.

JAEA Reports

Disassembly of JT-60 tokamak device and ancillary facilities for JT-60 tokamak

Okano, Fuminori; Ichige, Hisashi; Miyo, Yasuhiko; Kaminaga, Atsushi; Sasajima, Tadayuki; Nishiyama, Tomokazu; Yagyu, Junichi; Ishige, Yoichi; Suzuki, Hiroaki; Komuro, Kenichi; et al.

JAEA-Technology 2014-003, 125 Pages, 2014/03

JAEA-Technology-2014-003.pdf:13.32MB

The disassembly of JT-60 tokamak device and its peripheral equipments, where the total weight was about 5400 tons, started in 2009 and accomplished in October 2012. This disassembly was required process for JT-60SA project, which is the Satellite Tokamak project under Japan-EU international corroboration to modify the JT-60 to the superconducting tokamak. This work was the first experience of disassembling a large radioactive fusion device based on Radiation Hazard Prevention Act in Japan. The cutting was one of the main problems in this disassembly, such as to cut the wielded parts together with toroidal field coils, and to cut the vacuum vessel into two. After solving these problems, the disassembly completed without disaster and accident. This report presents the outline of the JT-60 disassembly, especially tokamak device and ancillary facilities for tokamak device.

JAEA Reports

Assembly work and transport of JT-60SA cryostat base

Okano, Fuminori; Masaki, Kei; Yagyu, Junichi; Shibama, Yusuke; Sakasai, Akira; Miyo, Yasuhiko; Kaminaga, Atsushi; Nishiyama, Tomokazu; Suzuki, Sadaaki; Nakamura, Shigetoshi; et al.

JAEA-Technology 2013-032, 32 Pages, 2013/11

JAEA-Technology-2013-032.pdf:8.86MB

Japan Atomic Energy Agency started to construct a fully superconducting tokamak experiment device, JT-60SA, to support the ITER since January, 2013 at the Fusion Research and Development Directorate in Naka, Japan. The JT-60SA will be constructed with enhancing the previous JT-60 infrastructures, in the JT-60 torus hall, where the ex-JT-60 machine was disassembled. The JT-60SA Cryostat Base, for base of the entire tokamak structure, were assembly as first step of this construction. The Cryostat Base (CB, 250 tons) is consists of 7 main made of stainless steel, 12m diameter and 3m height. It was built in the Spain and transported to the Naka site with the seven major parts split, via Hitachi port. The assembly work of these steps, preliminary measurements, sole plate adjustments of its height and flatness, and assembly of the CB. Introduces the concrete result of assembly work and transport of JT-60SA cryostat base.

JAEA Reports

Disassembly of JT-60 tokamak device

Okano, Fuminori; Ikeda, Yoshitaka; Sakasai, Akira; Hanada, Masaya; Ichige, Hisashi; Miyo, Yasuhiko; Kaminaga, Atsushi; Sasajima, Tadayuki; Nishiyama, Tomokazu; Yagyu, Junichi; et al.

JAEA-Technology 2013-031, 42 Pages, 2013/11

JAEA-Technology-2013-031.pdf:18.1MB

The disassembly of JT-60 tokamak device and its peripheral equipments, where the total weight was about 6200 tons, started in 2009 and accomplished in October 2012. This disassembly was required process for JT-60SA project, which is the Satellite Tokamak project under Japan-EU international corroboration to modify the JT-60 to the superconducting tokamak. This work was the first experience of disassembling a large radioactive fusion device based on Radiation Hazard Prevention Act in Japan. The cutting was one of the main problems in this disassembly, such as to cut the wielded parts together with toroidal field coils, and to cut the vacuum vessel into two. After solving these problems, the disassembly completed without disaster and accident. This report presents the outline of the JT-60 disassembly, especially tokamak device.

Journal Articles

Design and test of JT-60SA gas injection system

Miyo, Yasuhiko; Nakano, Tomohide; Sakurai, Shinji; Sakasai, Akira

Dai-18-Kai Bunshi Kagaku Kenkyusho Gijutsu Kenkyukai Hokokushu (CD-ROM), 5 Pages, 2012/00

no abstracts in English

Journal Articles

Inelastic neutron scattering on iron-based superconductor BaFe$$_2$$(As,P)$$_2$$

Ishikado, Motoyuki; Kodama, Katsuaki; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Wakimoto, Shuichi; Iyo, Akira*; Eisaki, Hiroshi*; Arai, Masatoshi; Shamoto, Shinichi

Physica C, 471(21-22), p.643 - 646, 2011/11

 Times Cited Count:4 Percentile:22.18(Physics, Applied)

Superconducting gap symmetry of $$Ln$$1111 system, which has the highest $$T_c$$ in iron-based superconductors, is considered to be full gap $$s_{pm}$$ wave based on magnetic penetration depth and neutron scattering measurements. On the other hand, a line node gap symmetry is proposed in BaFe$$_2$$(As,P)$$_2$$ based on magnetic penetration depth and thermal conductivity measurements despite comparatively its high-$$T_c$$ ($$T_c$$=30 K). Inelastic neutron scattering of BaFe$$_2$$(As,P)$$_2$$ may exhibit different magnetic excitations in the $$Q$$-position or $$E$$-dependence of a resonant peak from that of La1111 system. In this study, we performed inelastic neutron scattering measurement on 36g polycrystalline powder sample of optimally-doped BaFe$$_2$$(As,P)$$_2$$ using Fermi chopper spectrometer 4SEASONS in J-PARC. We will discuss about the possible superconducting gap symmetry based on our inelastic neutron scattering results.

Journal Articles

Neutron scattering of iron-based superconductors

Shamoto, Shinichi; Wakimoto, Shuichi; Kodama, Katsuaki; Ishikado, Motoyuki; Christianson, A. D.*; Lumsden, M. D.*; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Arai, Masatoshi; et al.

Physica C, 471(21-22), p.639 - 642, 2011/11

 Times Cited Count:0 Percentile:0(Physics, Applied)

We have studied low-energy spin excitations on polycrystalline LaFeAsO$$_{1-x}$$F$$_{x}$$ samples by inelastic neutron scattering. The dynamical spin susceptibility $$chi$$''($$omega$$) of the superconducting samples is found to be comparable to that of the magnetically ordered parent sample. On the other hand, $$chi$$''($$omega$$) almost vanishes at x=0.158, where the superconducting transition temperature T$$_{c}$$ is suppressed to 7 K. This suggests that the low energy spin excitations are closely connected with high-T$$_{c}$$ superconductivity. The disappearance of the spin excitations at low energy would correspond to the disappearance of the hole Fermi surface as the electron concentration increases with doping, as observed in ARPES measurements of BaFe$$_{2-x}$$Co$$_{x}$$As$$_{2}$$ at x=0.15. The relationship between the spin excitation and the Fermi surface will be discussed in comparison with other iron-based superconductors.

Journal Articles

$$s_{pm}$$-like spin resonance in the iron-based nodal superconductor BaFe$$_2$$(As$$_{0.65}$$P$$_{0.35}$$)$$_2$$ observed using inelastic neutron scattering

Ishikado, Motoyuki; Nagai, Yuki; Kodama, Katsuaki; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro; Wakimoto, Shuichi; Nakamura, Hiroki; Machida, Masahiko; Suzuki, Katsuhiro*; et al.

Physical Review B, 84(14), p.144517_1 - 144517_5, 2011/10

 Times Cited Count:26 Percentile:73.08(Materials Science, Multidisciplinary)

We performed inelastic neutron scattering on a powder sample of iron-based superconductor BaFe$$_2$$(As$$_{0.65}$$P$$_{0.35}$$)$$_2$$ with $$T_c$$ = 30 K. Although this system is expected to have line nodes in its superconducting order parameter, we have observed spin resonance at the same scattering vector as that appeared in the $$s_{pm}$$-wave iron-based superconductors without line nodes. Moreover, the resonance enhancement, which can be a measure of the area of sign reversal between the hole and electron Fermi surfaces (FSs), is comparable to those without line nodes. These facts indicate that the sign reversal between the FSs is still dominant in this system, and the line nodes should create only limited area of sign-reversal on a single FS. Hence the system can hold higher Tc than the other iron-based superconductors with nodal symmetry, such as LaFePO$$_{1-y}$$ and KFe$$_2$$As$$_2$$ ($$T_c <$$ 10 K).

Journal Articles

Soft and isotropic phonons in PrFeAsO$$_{1-y}$$

Fukuda, Tatsuo; Baron, A. Q. R.*; Nakamura, Hiroki; Shamoto, Shinichi; Ishikado, Motoyuki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.

Physical Review B, 84(6), p.064504_1 - 064504_13, 2011/08

 Times Cited Count:9 Percentile:41.39(Materials Science, Multidisciplinary)

Journal Articles

Angle-resolved photoemission spectroscopy study of PrFeAsO$$_{0.7}$$; Comparison with LaFePO

Nishi, Ichiro*; Ishikado, Motoyuki; Ideta, Shinichiro*; Malaeb, W.*; Yoshida, Teppei*; Fujimori, Atsushi*; Kotani, Yoshinori*; Kubota, Masato*; Ono, Kanta*; Yi, M.*; et al.

Physical Review B, 84(1), p.014504_1 - 014504_5, 2011/07

 Times Cited Count:22 Percentile:66.92(Materials Science, Multidisciplinary)

We have performed an angle-resolved photoemission spectroscopy (ARPES) study of the iron-based superconductor PrFeAsO$$_{0.7}$$ and examined the Fermi surfaces and band dispersions near the fermi level. Heavily hole-doped electronic states have been observed due to the polar nature of the cleaved surfaces. Nevertheless, we have found that the ARPES spectra basically agree with band dispersions calculated in the local density approximation (LDA) if the bandwidth is reduced by a factor of $$sim$$ 2.5 and then the chemical potential is lowered by $$sim$$ 70 meV. Comparison with previous ARPES results on LaFePO reveals that the energy positions of the $$d$$$$_{3z^{2}-r^{2}}$$- and $$d$$$$_{yz,zx}$$-derived bands are considerably different between the two materials, which we attribute to the different pnictogen height as predicted by the LDA calculation.

Journal Articles

Report of detaching of internal tile according to dismantlement of JT-60

Yagyu, Junichi; Miyo, Yasuhiko; Sasajima, Tadayuki; Sakasai, Akira; Shibanuma, Kiyoshi

Heisei-22-Nendo Kumamoto Daigaku Sogo Gijutsu Kenkyukai Hokokushu (CD-ROM), 4 Pages, 2011/03

no abstracts in English

Journal Articles

Storage and safety management of radioactive components for disassembly of JT-60 tokamak device

Nishiyama, Tomokazu; Okano, Fuminori; Miyo, Yasuhiko; Kubo, Hirotaka; Miya, Naoyuki; Oikawa, Akira; Sasajima, Tadayuki; Sakasai, Akira

Heisei-22-Nendo Kumamoto Daigaku Sogo Gijutsu Kenkyukai Hokokushu (CD-ROM), 5 Pages, 2011/03

no abstracts in English

Journal Articles

Structural analysis on iron-based superconductor Pr1111 system with oxygen deficiency and flourine substitution

Kodama, Katsuaki; Ishikado, Motoyuki; Esaka, Fumitaka; Iyo, Akira*; Eisaki, Hiroshi*; Shamoto, Shinichi

Journal of the Physical Society of Japan, 80(3), p.034601_1 - 034601_6, 2011/03

 Times Cited Count:12 Percentile:62.29(Physics, Multidisciplinary)

Journal Articles

Phonon spectra of PrFeAsO$$_{1-y}$$ via inelastic X-ray scattering

Fukuda, Tatsuo; Baron, A. Q. R.*; Nakamura, Hiroki; Shamoto, Shinichi; Ishikado, Motoyuki; Machida, Masahiko; Uchiyama, Hiroshi*; Iyo, Akira*; Kito, Hijiri*; Mizuki, Junichiro; et al.

Journal of the Physical Society of Japan, 80(Suppl.B), p.SB015_1 - SB015_4, 2011/01

 Times Cited Count:1 Percentile:11.83(Physics, Multidisciplinary)

We have investigated phonons of PrFeAsO$$_{1-y}$$ using high-resolution inelastic X-ray scattering and $$ab-initio$$ calculations. Extensive measurements show that there are some changes in phonon spectra with temperature and/or doping. However, we compare our data with several calculations and find that the experimentally observed changes are much smaller than differences between the experiment. data and the calculations. Agreement is improved if magnetism is included in the calculations. However, still in disagreement even in the parent sample below T$$_N$$. We consider several modifications of the $$ab-initio$$ calculations. The best agreement is obtained from modifying the nonmagnetic calculation. by softening only the in-plane nearest-neighbor Fe-As force constant. Fluctuating magnetism may be a partial explanation for the failure of the calculations, but seems incomplete in the face of the similarity of the measured phonon response in all the systems investigated including those known to have static magnetism.

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