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Suwa, Tomone*; Hemmi, Tsutomu*; Saito, Toru*; Takahashi, Yoshikazu*; Koizumi, Norikiyo*; Luzin, V.*; Suzuki, Hiroshi; Harjo, S.
IEEE Transactions on Applied Superconductivity, 28(3), p.6001104_1 - 6001104_4, 2018/04
Times Cited Count:1 Percentile:7.00(Engineering, Electrical & Electronic)Harjo, S.; Kawasaki, Takuro; Hemmi, Tsutomu; Ito, Takayoshi*; Nakamoto, Tatsushi*; Aizawa, Kazuya
JPS Conference Proceedings (Internet), 8, p.031001_1 - 031001_5, 2015/09
Ninomiya, Hiromasa; Akiba, Masato; Fujii, Tsuneyuki; Fujita, Takaaki; Fujiwara, Masami*; Hamamatsu, Kiyotaka; Hayashi, Nobuhiko; Hosogane, Nobuyuki; Ikeda, Yoshitaka; Inoue, Nobuyuki; et al.
Journal of the Korean Physical Society, 49, p.S428 - S432, 2006/12
To contribute DEMO and ITER, the design to modify the present JT-60U into superconducting coil machine, named National Centralized Tokamak (NCT), is being progressed under nationwide collaborations in Japan. Mission, design and strategy of this NCT program is summarized.
Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Kuzushita, Kaori; Inami, Toshiya; Owada, Kenji; Maekawa, Sadamichi*; Masui, Takahiko*; Tajima, Setsuko*; et al.
AIP Conference Proceedings 850, p.445 - 446, 2006/09
Mott gap excitations in the optimally doped high- superconductor YBa
Cu
O
(
= 93 K) have been studied by the resonant inelastic X-ray scattering method. Anisotropic spectra in the
-plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the
direction, while the excitation from the CuO
plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra when different values of the on-site Coulomb energy are assumed. The Mott gap of the CuO chain site is found to be much smaller than that of the CuO
plane site.
Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Maekawa, Sadamichi*; Hoesch, M.; Kuzushita, Kaori; Inami, Toshiya; Tsubota, Masami; Yamada, Kazuyoshi*; et al.
AIP Conference Proceedings 850, p.403 - 404, 2006/09
We report a resonant inelastic X-ray scattering (RIXS) study of charge excitations in the electron-doped high- superconductor Nd
Ce
CuO
. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with
-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.
Hamada, Kazuya; Nakajima, Hideo; Kawano, Katsumi; Takano, Katsutoshi*; Tsutsumi, Fumiaki*; Seki, Shuichi*; Okuno, Kiyoshi; Fujitsuna, Nobuyuki*; Mizoguchi, Mitsuru*
IEEE Transactions on Applied Superconductivity, 16(2), p.787 - 790, 2006/06
Times Cited Count:6 Percentile:36.97(Engineering, Electrical & Electronic)no abstracts in English
Koizumi, Norikiyo; Nishimura, Arata*
Nihon Genshiryoku Gakkai-Shi, 47(10), p.703 - 708, 2005/10
no abstracts in English
Tateiwa, Naoyuki; Haga, Yoshinori; Matsuda, Tatsuma; Ikeda, Shugo; Yasuda, Takashi*; Takeuchi, Tetsuya*; Settai, Rikio*; Onuki, Yoshichika
Journal of the Physical Society of Japan, 74(7), p.1903 - 1906, 2005/07
Times Cited Count:73 Percentile:89.03(Physics, Multidisciplinary)The pressure dependences of the antiferromagnetic and superconducting transition temperatures have been investigated by ac heat capacity measurement under high pressures for the heavy-fermion superconductor CePtSi without inversion symmetry in the tetragonal structure. The N
el temperature
= 2.2 K decreases with increasing pressure and becomes zero at the critical pressure
0.6 GPa. On the other hand, the superconducting phase exists in a wider pressure region from ambient pressure to about 1.5 GPa. The pressure phase diagram of CePt
Si is thus very unique and has never been reported before for other heavy fermion superconductors.
Koizumi, Norikiyo; Matsui, Kunihiro; Kume, Etsuo; Okuno, Kiyoshi
IEEE Transactions on Applied Superconductivity, 15(2), p.1363 - 1366, 2005/06
Times Cited Count:0 Percentile:0.00(Engineering, Electrical & Electronic)The NbAl Insert was developed by JAERI aiming at the demonstration of a Nb
Al conductor to fusion reactor magnets. A quench test was performed on the Nb
Al Insert at 13 T with various temperature margins, which are defined as a difference between current sharing temperature and operating temperature. The initial normalcy was initiated by using an inductive heater and a coil current was kept for several seconds. The normal zone propagation velocity was accelerated after 3 s from the onset of heating in case that the temperature margin was set at 0.5 K. A simulation using one-dimensional stability and quench simulation code was performed. The calculation results indicate that such rapid propagation occurred due to a temperature rise beyond a current sharing temperature because of a large pressure increase even at the location where the normal front did not reach yet. This large pressure rise was caused since the coolant was contained in the closed circulation circuit of the cooling system, which is usually applied to a large magnet cooling system.
Nomura, Takuji
Journal of the Physical Society of Japan, 74(6), p.1818 - 1829, 2005/06
Times Cited Count:27 Percentile:73.87(Physics, Multidisciplinary)We provide a detailed quantitative analysis of transport properties in the -wave superconducting state of Sr
RuO
. Specifically, we calculate ultrasound attenuation rate and electronic thermal conductivity within the mean field approximation. The momentum dependence of the gap function is determined by solving the Eliashberg equation for a three-band Hubbard model with the realistic electronic structure of Sr
RuO
. Consequently, we obtain the temperature dependence of the transport coefficients in agreement with the experimental results.
Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Maekawa, Sadamichi*; Hoesch, M.; Kuzushita, Kaori; Tsubota, Masami; Inami, Toshiya; Mizuki, Junichiro; et al.
Physical Review Letters, 94(20), p.207003_1 - 207003_4, 2005/05
Times Cited Count:75 Percentile:89.38(Physics, Multidisciplinary)We report a resonant inelastic X-ray scattering (RIXS) study of charge excitations in the electron-doped high- superconductor Nd
Ce
CuO
. The intraband and interband excitations across the Fermi energy are separated for the first time by tuning the experimental conditions properly to measure charge excitations at low energy. A dispersion relation with
-dependent width emerges clearly in the intraband excitation, while the intensity of the interband excitation is concentrated around 2 eV near the zone center. The experimental results are consistent with theoretical calculation of the RIXS spectra based on the Hubbard model.
Ishii, Kenji; Tsutsui, Kenji*; Endo, Yasuo*; Toyama, Takami*; Kuzushita, Kaori; Inami, Toshiya; Owada, Kenji; Maekawa, Sadamichi*; Masui, Takahiko*; Tajima, Setsuko*; et al.
Physical Review Letters, 94(18), p.187002_1 - 187002_4, 2005/05
Times Cited Count:40 Percentile:80.45(Physics, Multidisciplinary)Mott gap excitations in the optimally doped high- superconductor YBa
Cu
O
(
= 93 K) have been studied by the resonant inelastic X-ray scattering method. Anisotropic spectra in the
-plane are observed in a twin-free crystal. The excitation from the one-dimensional CuO chain is enhanced at 2 eV near the zone boundary of the
direction, while the excitation from the CuO
plane is broad at 1.5-4 eV and almost independent of the momentum transfer. Theoretical calculation based on the one-dimensional and two-dimensional Hubbard model reproduces the observed spectra when different values of the on-site Coulomb energy are assumed. The Mott gap of the CuO chain site is found to be much smaller than that of the CuO
plane site.
Shamoto, Shinichi; Hirai, Atsuo*; Yamanaka, Shoji*; Aso, Naofumi*; Kajitani, Tsuyoshi*
Journal of Neutron Research, 12(4), p.295 - 300, 2004/12
Inelastic neutron scattering measurements have been performed on superconducting NaHfNCl powder samples with x=0.27 and 0.38 (T
=22 K). We have observed several temperature dependent phonon anomalies, e.g., at E=15, 29, 76, and 81 meV for the former sample. A phonon peak with E=14.5 meV at Q=6
increases for both samples with decreasing temperature below T=40 K, which is much higher than T
. The phonon peak is assigned to an ab-plane vibrational mode, E
, of chlorine and hafnium atoms, which strongly modifies the electronic band structure. The phonon anomaly is discussed in terms of carrier inhomogeneity.
Ishikawa, Norito; Van der Beek, C. J.*; Dunlop, A.*; Jaskierowicz, G.*; Li, M.*; Kes, P. H.*; Della-Negra, S.*
Journal of the Physical Society of Japan, 73(10), p.2813 - 2821, 2004/10
Times Cited Count:3 Percentile:26.13(Physics, Multidisciplinary)By irradiating 30MeV C fullerene beam, we have produced tracks of diameter 20nm and length 200nm near the surface of single crystalline Bi
Sr
CaCu
O
. Both the critical current density and magnetic irreversibility line are significantly enhanced. The irradiated crystals have shown salient features of the (
,
) vortex phase diagram of vortex matter both of unirradiated sample, such as the first order vortex phase transition, and the exponential Bose glass line characteristic of heavy ion-irradiated crystals.
Nishio, Taichiro; Okayasu, Satoru; Suzuki, Junichi; Kadowaki, Kazuo
Physica C, 412-414(Part1), p.379 - 384, 2004/10
We have studied the vortex states in a meoscopic superconductor with geometrical constraints such as disks, triangles, squares, etc. with dimensions between 30-50m using a scanning SQUID microscope (SQM2000,Seiko Instruments Inc.). The sample was fabricated by electron lithography and Focused Ion Beam (FIB) techniques. Quantized vortices enter into a mesoscopic superconductor discretely as a function of magnetic field accompanied by the sequential step-wise jump of magnetization of the superconductor. Quantitative as well as qualitative analyses of spatial vortex arrangement as a function of the number of vortices will be shown in comparison with the recent theoretical predictions.
Okuno, Kiyoshi
Chodendo Web 21 (Internet), (2004年8月), P. 1, 2004/08
no abstracts in English
Okuno, Kiyoshi; Shikov, A.*; Koizumi, Norikiyo
Journal of Nuclear Materials, 329-333(Part1), p.141 - 147, 2004/08
Times Cited Count:15 Percentile:67.40(Materials Science, Multidisciplinary)A tokamak fusion reactor requires a superconducting magnet system for plasma confinement and control. Higher magnetic field of the toroidal field (TF) coil can offer better performance of the reactor. Therefore, fusion magnet development always drives a new superconductor to be used in a large magnet on an industrial basis. Magnets for the International Thermonuclear Experimental Reactor (ITER) use NbSn in order to generate a peak magnetic field of 13 T. Technologies for Nb
Sn superconductor has made a significant progress through the extensive development in ITER including the manufacture of the full-scale model coils. A next generation superconductor, Nb
Al, has outstanding features of large critical current density at the high field. High Tc (Critical Temperature) superconductor (HTS) is another candidate, and if it becomes available, a magnetic filed above 20 T can be realized in fusion reactor. However, technical issues have to be solved for the application of these innovate superconducting materials in Fusion Reactor.
Okuno, Kiyoshi
IEEE Transactions on Applied Superconductivity, 14(2), p.1376 - 1381, 2004/06
Times Cited Count:6 Percentile:36.38(Engineering, Electrical & Electronic)Fusion magnets have major features of a large size, high magnetic field and operation under huge electromagnetic forces together with nuclear radiation. From this point of view, new design principles and fabrication concepts were proposed to build the ITER CS, and a model coil programme was performed for verification. The model coil reached its design point of 13 T and 46 kA, achieving all the goals of the development programme, including the following areas: (1) high-performance NbSn strand and mass production of about 26.5 t, (2) high-strength jacket materials (Incoloy 908, titanium, stainless steel) that can undergo Nb
Sn heat treatment, (3) 46 kA cable-in-conduit conductors in a total length of 5 km, (4) insulation materials that can withstand up to 10 MGy radiation dose, (5) fabrication using wind-react-and-transfer method that enables Nb3Sn application to a large magnet with mechanically rigid and high-voltage insulated windings. Results and experiences from the programme are being fed back into the design and QA requirements of the ITER magnets.
Isono, Takaaki; Hamada, Kazuya; Kawano, Katsumi; Abe, Kanako*; Nunoya, Yoshihiko; Sugimoto, Makoto; Ando, Toshinari*; Okuno, Kiyoshi; Bono, Takaaki*; Tomioka, Akira*; et al.
Teion Kogaku, 39(3), p.122 - 129, 2004/03
JAERI has been developing a large-capacity high-temperature superconductor (HTS) current lead for fusion application, and succeeded in fabricating and testing a 60kA HTS current lead satisfying ITER requirements. Targets of performance are 1/10 heat leak and 1/3 electric power consumption of cryogenic system compared with a conventional lead. To achieve the target, selection of sheath material of HTS, optimizing the Cu part, reduction of joule heat at joint between HTS and Cu parts, improve of heat transfer between HTS and stainless steel tube. Developed 60kA HTS current lead satisfied the design condition and almost achieved the targets. Adoption of the HTS current lead can reduce 13% electric power consumption of cryogenic system for ITER.
Inaguchi, Takashi*; Hasegawa, Mitsuru*; Koizumi, Norikiyo; Isono, Takaaki; Hamada, Kazuya; Sugimoto, Makoto; Takahashi, Yoshikazu
Cryogenics, 44(2), p.121 - 130, 2004/02
Times Cited Count:6 Percentile:27.51(Thermodynamics)In order to analyze the quench characteristic of a cable-in-conduit (CIC) conductor that has a sub-cooling channel at the center of conductor cross section, an axisymmetrical two-dimensional calculation model was developed. The test and calculation results of the CS insert were compared regarding the pressure drop and the behavior of the total voltage, temperature and normal zone propagation in the quench. They show good agreement. Therefore, the effectiveness of the calculation model is verified. It was also found that there is coolant convection between the central channel and bundle region even in a steady state. This makes the pressure drop in the central channel larger than that in a cylindrical pipe which has a smooth surface. In addition, it was found that the higher temperature of the coolant flowing through the central channel heats the coolant and the cable in the bundle region. It can be said that the hot coolant flowing through the central channel accelerates normal zone propagation.