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Journal Articles

Evaluation of thermal strain induced in components of Nb$$_{3}$$Sn strand during cooling

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:0 Percentile:100(Engineering, Electrical & Electronic)

Journal Articles

Thermal strain in superconducting Nb$$_{3}$$Sn strand at cryogenic temperature

Harjo, S.; Kawasaki, Takuro; Hemmi, Tsutomu; Ito, Takayoshi*; Nakamoto, Tatsushi*; Aizawa, Kazuya

JPS Conference Proceedings (Internet), 8, p.031001_1 - 031001_5, 2015/09

Journal Articles

Overview of national centralized tokamak program; Mission, design and strategy to contribute ITER and DEMO

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.

Journal Articles

Momentum dependence of Mott gap excitations in optimally doped YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ studied by resonant inelastic X-ray scattering

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-$$T_{c}$$ superconductor YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ ($$T_{c}$$ = 93 K) have been studied by the resonant inelastic X-ray scattering method. Anisotropic spectra in the $$ab$$-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 $$b^{*}$$ direction, while the excitation from the CuO$$_2$$ 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$$_2$$ plane site.

Journal Articles

Doping Momentum dependence of charge dynamics in Nd$$_{2-x}$$Ce$$_{x}$$CuO$$_4$$ (x=0, 0.075, and 0.15) studied by Resonant inelastic X-ray scattering

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-$$T_{c}$$ superconductor Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$. 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 $${mathbf q}$$-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.

Journal Articles

Demonstration of JK2LB jacket fabrication for ITER central solenoid

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:60.32(Engineering, Electrical & Electronic)

no abstracts in English

Journal Articles

Intelligible seminar on fusion reactors, 9; Superconducting coil to generate magnetic field for plasma confinement

Koizumi, Norikiyo; Nishimura, Arata*

Nippon Genshiryoku Gakkai-Shi, 47(10), p.703 - 708, 2005/10

no abstracts in English

Journal Articles

Novel pressure phase diagram of heavy fermion superconductor CePt$$_{3}$$Si investigated by ac calorimetry

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:66 Percentile:10.41(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 CePt$$_3$$Si without inversion symmetry in the tetragonal structure. The N$'e$el temperature $$T_{rm N}$$ = 2.2 K decreases with increasing pressure and becomes zero at the critical pressure $$P_{rm AF}$$ $$simeq$$ 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$$_3$$Si is thus very unique and has never been reported before for other heavy fermion superconductors.

Journal Articles

Rapid normal zone propagation observed in a 13 T-46 kA Nb$$_{3}$$Al cable-in-conduit conductor

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:100(Engineering, Electrical & Electronic)

The Nb$$_{3}$$Al Insert was developed by JAERI aiming at the demonstration of a Nb$$_{3}$$Al conductor to fusion reactor magnets. A quench test was performed on the Nb$$_{3}$$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.

Journal Articles

Theory of transport properties in the $$p$$-wave superconducting state of Sr$$_2$$RuO$$_4$$; A Microscopic determination of the gap structure

Nomura, Takuji

Journal of the Physical Society of Japan, 74(6), p.1818 - 1829, 2005/06

 Times Cited Count:22 Percentile:27.28(Physics, Multidisciplinary)

We provide a detailed quantitative analysis of transport properties in the $$p$$-wave superconducting state of Sr$$_2$$RuO$$_4$$. 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$$_2$$RuO$$_4$$. Consequently, we obtain the temperature dependence of the transport coefficients in agreement with the experimental results.

Journal Articles

Momentum dependence of charge excitations in the electron-doped superconductor Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$; A Resonant inelastic X-ray scattering study

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:63 Percentile:10.79(Physics, Multidisciplinary)

We report a resonant inelastic X-ray scattering (RIXS) study of charge excitations in the electron-doped high-$$T_{c}$$ superconductor Nd$$_{1.85}$$Ce$$_{0.15}$$CuO$$_4$$. 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 $${mathbf q}$$-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.

Journal Articles

Mott gap excitations in twin-free YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ ($$T_{c}$$ = 93 K) studied by resonant inelastic X-ray scattering

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:38 Percentile:17.94(Physics, Multidisciplinary)

Mott gap excitations in the optimally doped high-$$T_{c}$$ superconductor YBa$$_2$$Cu$$_3$$O$$_{7-delta}$$ ($$T_{c}$$ = 93 K) have been studied by the resonant inelastic X-ray scattering method. Anisotropic spectra in the $$ab$$-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 $$b^{*}$$ direction, while the excitation from the CuO$$_2$$ 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$$_2$$ plane site.

Journal Articles

Phonon anomaly on Na$$_x$$HfNCl superconductors with ${it T}$$$_c$$=22 K

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 Na$$_x$$HfNCl powder samples with x=0.27 and 0.38 (T$$_c$$ =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 $AA $^{-1}$$ increases for both samples with decreasing temperature below T=40 K, which is much higher than T$$_c$$. The phonon peak is assigned to an ab-plane vibrational mode, E$$_u$$, of chlorine and hafnium atoms, which strongly modifies the electronic band structure. The phonon anomaly is discussed in terms of carrier inhomogeneity.

Journal Articles

Vortex phase diagram in Bi$$_{2}$$Sr$$_{2}$$CaCu$$_{2}$$O$$_{8+delta}$$ with damage tracks created by 30 MeV fullerene irradiation

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:1 Percentile:87.91(Physics, Multidisciplinary)

By irradiating 30MeV C$$_{60}$$ fullerene beam, we have produced tracks of diameter 20nm and length 200nm near the surface of single crystalline Bi$$_{2}$$Sr$$_{2}$$CaCu$$_{2}$$O$$_{8+delta}$$. Both the critical current density and magnetic irreversibility line are significantly enhanced. The irradiated crystals have shown salient features of the ($$B$$,$$T$$) 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.

Journal Articles

Penetration of vortices into micro-superconductors observed with a scanning SQUID microscope

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 30-50$$mu$$m 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.

Journal Articles

Journal Articles

Superconducting magnet system in a fusion reactor

Okuno, Kiyoshi; Shikov, A.*; Koizumi, Norikiyo

Journal of Nuclear Materials, 329-333(Part1), p.141 - 147, 2004/08

 Times Cited Count:11 Percentile:37.16(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 Nb$$_{3}$$Sn in order to generate a peak magnetic field of 13 T. Technologies for Nb$$_{3}$$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$$_{3}$$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.

Journal Articles

Progress in the superconducting magnet technology through the ITER CS model coil programme

Okuno, Kiyoshi

IEEE Transactions on Applied Superconductivity, 14(2), p.1376 - 1381, 2004/06

 Times Cited Count:6 Percentile:61.42(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 Nb$$_{3}$$Sn strand and mass production of about 26.5 t, (2) high-strength jacket materials (Incoloy 908, titanium, stainless steel) that can undergo Nb$$_{3}$$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.

Journal Articles

Development and test results of a 60kA HTS current lead for fusion application

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.

Journal Articles

Quench analysis of an ITER 13T-40kA Nb$$_{3}$$Sn coil (CS insert)

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:70.28(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.

116 (Records 1-20 displayed on this page)