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337 results on '"Iwakuma, M."'

51. Development of a 1T cryocooler-cooled pulse coil with a Bi2223 superconducting parallel conductor for SMES

Author

Iwakuma, M., Funaki, K., Kajikawa, K., Kanetaka, H., Hayashi, H., Tsutsumi, K., Tomioka, A., Konno, M., and Nose, S.

Subjects
Electric coils -- Design and construction, Magnetic energy storage -- Research, Superconducting magnets -- Design and construction, Superconductors -- Electric properties, Business, Electronics, Electronics and electrical industries
Abstract

The design and fabrication of a 1T cryocooler-cooled pulse coil operating at 40 K are described. To realize a uniform current distribution and to lessen the alternating current loss density down to the level of a single strand, a 4-strand interlayer-transposed parallel conductor composed of Bi2223 rectangular cross-sectional multifilamentary wires was adopted. Results indicate that the highest temperature of the coil was 40.5 K and the difference in temperature inside the winding was about 2 K.

Published
1999

52. Experimental results of the model coil for cooling design of a 1T cryocooler-cooled pulse coil for SMES

Author

Tomioka, a., Bohno, T., Nose, S., Konno, M., Iwakuma, M., Funaki, K., Kajikawa, K., Kanetaka, H., Hayashi, H., and Tsutsumi, K.

Subjects
Electric coils -- Models, High temperature superconductivity -- Research, Magnetic energy storage -- Research, Superconducting magnets -- Design and construction, Business, Electronics, Electronics and electrical industries
Abstract

Research was conducted to evaluate a high temperature superconducting (HTS) cooling model coil for superconducting magnet energy storage. The objective was to make a HTS coil that is cooled to 40 K by a single-stage cryocooler and continuously operated at 1 Hz with a field amplitude of 1 T. The cooling model coil system was made to examine the effective arrangement of the heat drains. Results indicate that the HTS coil temperature is 43 K level when the alternating current losses are about 7 W and the temperature difference between HTS conductor and AIN plate is estimated to be 0.2 K.

Published
1999

56. Preliminary tests of a 500 kVA-class oxide superconducting transformer cooled by subcooled nitrogen

Author

Funaki, K., Iwakuma, M., Takeo, M., Yamafuji, K., Suehiro, J., Hara, M., Konno, M., Kasagawa, Y., Itoh, I., Nose, S., Ueyama, M., Hayashi, K., and Sato, K.

Subjects
Current transformers (Instrument transformer) -- Testing, Magnetic tapes -- Research, Superconductors -- Thermal properties, Business, Electronics, Electronics and electrical industries
Abstract

A 500 kVa-class oxide superconducting transformer for subcooled nitrogen operations was designed, constructed and tested. Three- and six-strand parallel conductors of Bi-2223 silver-sheathed multifilamentary tapes acted as the primary and secondary windings, respectively. The transformer was then installed in a continuous flow subcooled nitrogen system. It was operated up to critical current levels of 66 K without quenching.

Published
1997

57. Electromagnetic properties in parallel conductors composed of Bi2223 multifilamentary wires for power transformer windings

Author

Iwakuma, M., Funaki, K., Shinohara, H., Saohara, T., Takeo, M., Yamafuji, K., Konno, M., Kasagawa, Y., Okubo, K., Itoh, I., Nose, S., Ueyama, M., Hayashi, K., and Sato, K.

Subjects
Alternating current -- Research, Magnetic fields -- Research, Electric conductors -- Research, Electromagnetic measurements -- Research, Business, Electronics, Electronics and electrical industries
Abstract

A theoretical study was conducted on the alternating current losses in superconducting parallel conductors consisting of Bi2223 multifilamentary wires for power transformer windings. An analytical expression was developed for the additional coupling loss. The current distribution in solenoidal coil strands of the parallel conductor was also calculated experimentally and the influence of transposition on current distribution was examined.

Published
1997

59. Effects of artificial pins on the flux pinning force and other superconducting properties in NbTi superconductors

Author

Matsumoto, K., Tanaka, Y., Yamafuji, K., Funaki, K., Iwakuma, M., and Matsushita, T.

Subjects
Flux pinning -- Research, Niobium alloys -- Research, Superconductors -- Magnetic properties, Business, Electronics, Electronics and electrical industries
Abstract

Changes in the flux pinning force and other superconducting features of NbTi superconductors due to ribbon-shaped artificial pins were examined. Experimental analysis involved the utilization of superconductivity and magnetization measurements. Results of the experiment were subjected to theoretical verification. It was found that artificial pins significantly enhance the critical current density of the NbTi superconductors.

Published
1993

60. Additional A.C. losses due to alternating magnetic field component longitudinal to strand axis in the armature winding of fully superconducting generators

Author

Funaki, K., Kanetaka, H., Ueda, H., Yoshiya, F., Iwakuma, M., Takeo, M., and Yamafuji, K.

Subjects
Electric generators -- Windings, Armatures -- Research, Superconducting generators -- Research, Business, Electronics, Electronics and electrical industries
Abstract

Atheoretical study of additional ac losses in the armature winding of a superconducting generator is presented. The analysis, which concerns multiply-layered cables composed of multifilamentary superconductors, was conducted under conditions of an applied ac transport current and ac transverse magnetic field. To lower the total ac loss, issues related to the optimization of the winding's cable structures are also presented.

Published
1993

73. Thickness dependence of ac losses in circular disks of YBa[sub 2]Cu[sub 3]O[sub 7] films in perpendicular magnetic fields.

Author

Suenaga, M., Li, Q., Ye, Z., Iwakuma, M., Toyota, K., Funaki, F., Foltyn, S.R., Wang, H., and Clem, John R.

Subjects
THICKNESS measurement, ALTERNATING currents, SEMICONDUCTOR films, MAGNETIC fields, PULSED laser deposition, MODELS & modelmaking
Abstract

The ac losses in three disk-shaped YBa[sub 2]Cu[sub 3]O[sub 7] (YBCO) films, which were deposited on SrTiO[sub 3] by the pulsed-laser-deposition technique and had thicknesses, d, of 0.2, 1.0, and 3.0 μm, were measured in perpendicular applied ac magnetic fields to ∼0.14 T at 10 Hz in liquid nitrogen. The losses at low fields were found to be a strong function of the film thickness. The measured losses were compared with the theoretically calculated losses. The ac losses calculated using a field-independent critical-current density, the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 50, 9355 (1994)], agreed very well with the 0.2-μm-thick film, while the calculated losses agreed well with the measured ones when a field-dependent critical-current density, the Kim model [D. V. Shantsev, Y. M. Galperin, and T. H. Johansen, Phys. Rev. B 61, 9699 (2000)], was used for the films of thickness 1.0 and 3.0 μm. However, a surprising discrepancy was found in the values of B[sub c] and B[sub 0] for thinner YBCO films depending on whether they were determined by ac or dc measurements. B[sub c] is defined as B[sub c]=μ[sub 0]J[sub c](0)d/2, B[sub 0] is the characteristic field in the Kim-model critical-current density J[sub cK](B[sub a])=J[sub c](0)/(1+B[sub a]/B[sub 0]), and J[sub c](0) is the critical-current density at applied magnetic field B[sub a]=0. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Published
2004
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74. ac losses in circular disks of thin YBa[sub 2]Cu[sub 3]O[sub 7] films in perpendicular magnetic fields.

Author

Suenaga, M., Solovyov, V. F., Li, Q., Ye, Z., Wiesmann, H. J., Iwakuma, M., Fukui, M., Toyota, K., Funaki, F., Johansen, T. H., Shantsev, D. V., and Clem, J. R.

Subjects
ALTERNATING currents, THIN films, MAGNETIC fields, SEMICONDUCTOR films
Abstract

The ac losses at 20 and 30 Hz were measured for two disk-shaped YBa[sub 2]Cu[sub 3]O[sub 7] films in perpendicular peak applied magnetic fields up to ∼0.2 T in liquid nitrogen. One of the films had a significantly higher critical-current density than the other as determined from the loss measurements. Also, it exhibited a more-uniform flux penetration around the circumference of the disk than the other as observed by magneto-optical images of these films in perpendicular dc fields. The results from this film were compared with theoretical predictions of ac losses for disks of thin superconducting films in perpendicular magnetic fields using the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 55, 9355 (1994)], and the Kim critical-current model [D. V. Shantsev et al., Phys. Rev. B 61, 9699 (2000)]. The asymptotic Bean model predictions for low and high fields were in reasonably good agreement with the data. The numerical calculation of the losses following Shantsev et al. was found to give extremely good agreement with the loss data throughout the entire field range of the measurement when the Kim model for the critical-current density was used. [ABSTRACT FROM AUTHOR]

Published
2003
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75. Fabrication of 1 kA class oxide superconducting transformer cooled by cryocooler for AC transport measurement

Author

Department of Computer Science and Electronics, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka 820-8502, Japan, Research Institute of Superconductivity, Graduate School of Information Science and Electrical Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan, Fuji Electric Corporate Research and Development, Ltd., 7 Yawata-kaigandori, Ichihara-shi, Chiba 290-8511, Japan, Otabe, Edmund Soji, Yasuda, Takashi, Matsushita, Teruo, Iwakuma, M., Bohno, T., Department of Computer Science and Electronics, Kyushu Institute of Technology, 680-4 Kawazu, Iizuka 820-8502, Japan, Research Institute of Superconductivity, Graduate School of Information Science and Electrical Engineering, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan, Fuji Electric Corporate Research and Development, Ltd., 7 Yawata-kaigandori, Ichihara-shi, Chiba 290-8511, Japan, Otabe, Edmund Soji, Yasuda, Takashi, Matsushita, Teruo, Iwakuma, M., and Bohno, T.

Abstract

type:Journal Article, An AC current source of 1000 A class for AC transport measurements was designed and fabricated with using an oxide superconducting current transformer. Two cryocoolers were installed for cooling the transformer and a sample holder separately. A parallel conductor composed of six tapes was wound for a secondary winding and a transposition was performed to make the current distribution uniform in the parallel conductor. Temperatures of the transformer and the sample holder were controlled in the range of 35–50 and 25–77 K, respectively. The peak current in the secondary winding was over 1000 A in the frequency range of 1–75 Hz, when the primary peak current was 14 A., source:http://www.sciencedirect.com/science/journal/09214534

Published
2017

76. Effects of artificial pins on the flux pinning force and other superconducting properties in NbTi superconductors

Author

Furukawa Electric Co. Ltd., Yokohama, Furukawa Electric Co. Ltd., Yokohama（Kyushu Institute of Technology), Matsumoto, K, Tanaka, Y, Yamafuji, K, Funaki, K, Iwakuma, M, Matsushita, Teruo, Furukawa Electric Co. Ltd., Yokohama, Furukawa Electric Co. Ltd., Yokohama（Kyushu Institute of Technology), Matsumoto, K, Tanaka, Y, Yamafuji, K, Funaki, K, Iwakuma, M, and Matsushita, Teruo

Abstract

type:Journal Article, A marked enhancement of global pinning strength in Nb-50 wt.%Ti alloy was obtained by introducing ribbon-shaped artificial pins. Simultaneously, however, depression of Bc2 was observed. This behavior is analyzed theoretically, and a satisfactory explanation of the experimental results is obtained, source:DOI: 10.1109/77.233646

Published
2017

83. New Method for Quick Decay of Shielding Current in REBCO Superconducting Coils

Author

Iwakuma, M., primary, Tsukigi, Y., additional, Nabekura, K., additional, Ueno, T., additional, Shindo, R., additional, Kawahara, F., additional, Honda, S., additional, Tamura, K., additional, Yun, K., additional, Sato, S., additional, Yoshida, K., additional, Tomioka, A., additional, Konno, M., additional, Izumi, T., additional, Machi, T., additional, and Ibi, A., additional

Published
2016
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84. Relaxation of Shielding Current in Test Coils for MRI With REBCO Superconducting Scribed Tapes

Author

Iwakuma, M., primary, Tsukigi, Y., additional, Nabekura, K., additional, Ueno, T., additional, Shindo, R., additional, Kawahara, F., additional, Honda, S., additional, Tamura, K., additional, Yun, K., additional, Sato, S., additional, Yoshida, K., additional, Tomioka, A., additional, Konno, M., additional, Izumi, T., additional, Machi, T., additional, and Ibi, A., additional

Published
2016
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90. The short-circuit test results of 6.9kV/2.3kV 400kVA-class YBCO model transformer with fault current limiting function

Author

Tomioka, A., primary, Bohno, T., additional, Kakami, S., additional, Isozaki, M., additional, Watanabe, K., additional, Toyama, K., additional, Sugiyama, S., additional, Konno, M., additional, Gosho, Y., additional, Okamoto, H., additional, Hayashi, H., additional, Tsutsumi, T., additional, Iwakuma, M., additional, Saito, T., additional, Tanabe, K., additional, and Shiohara, Y., additional

Published
2013
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93. Development of a REBCO Superconducting Transformer With Current Limiting Function

Author

Iwakuma, M., primary, Tomioka, A., additional, Otonari, T., additional, Ogata, T., additional, Tsutsumi, T., additional, Sato, S., additional, Hayashi, H., additional, Okamoto, H., additional, Iijima, Y., additional, Saitoh, T., additional, Aoki, Y., additional, Koizumi, T., additional, Hasegawa, T., additional, Ohkuma, T., additional, Gosho, Y., additional, Yamada, Y., additional, Izumi, T., additional, and Shiohara, Y., additional

Published
2011
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