Y. Iijima

Fujikura Ltd., Edo, Tōkyō, Japan

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Publications (85)61.32 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A 25-T cryogen-free superconducting magnet (25T-CSM) is being developed at the High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. In the case of a cryogen-free superconducting magnet, the coil temperature rises during a sweep of an operating current due to ac losses. Hence, the ac loss estimation is very important for the cooling design. The critical current density and the magnetization of Gd123 tapes at 4.2 K were measured in order to estimate the ac loss of a Gd123 insert of the 25T-CSM. The ac loss is actually the hysteresis loss, which are calculated from the Jc properties taking the magnetic field distribution in the Gd123 coil into account. Regarding the effect of tape stacking (or winding) in a pancake coil, the slab approximation can be used for hysteresis loss calculation. In the case of slab model, the full penetration field at the center of the tape becomes higher than the maximum applied magnetic field in the most part of the coil. As a result, the hysteresis loss increases with increasing a magnetic field when the magnet energizes. The hysteresis losses assuming the slab model, however, show an opposite field dependence to those calculated from the strip model without the stacking effect. Hence, the ac loss of 5 W is estimated when the magnet energizes to 25.5 T within 60 min.
    IEEE Transactions on Applied Superconductivity 06/2015; 25(3):1-5. DOI:10.1109/TASC.2014.2366552 · 1.24 Impact Factor
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    ABSTRACT: High temperature superconducting (HTS) cables are able to achieve large power capacity and low-loss power transmission. Fujikura Ltd. worked on developing a 66 kV-5 kArms HTS power cable using high critical current (I-c) REBCO tapes in the Japanese national project. One of the technical targets in this project was to reduce AC loss to less than 2 W/m at 5 kArms. REBCO tapes with 240 A/4 mm-width of I-c at 77 K, self field, which were fabricated by ion-beam-assisted-deposition (IBAD) and pulsed laser deposition (PLD) methods, were applied to the HTS power cable. As a result, we succeeded in developing the 20 m-long 66 kV-5 kArms HTS power cable. The measured AC loss was achieved 1.4 W/m at 77 K and 1.0 W/m at 67 K at 5 kArms. On the other hand, it is considered that the eddy current loss of the stainless-steel cryostat pipe of HTS cable become obvious in the case of the single-core cable with the large current capacity. It is suggested that the eddy current loss of the stainless-steel cryostat pipe is due to the internal magnetic flux. Therefore, the eddy current loss of the stainless-steel cryostat pipe as well as uniform current distribution of HTS conductor and shield layer should be taken into account for designing the winding direction and pitch of HTS conductor and shield layer of HTS cable. In this work, the measured eddy current loss of the stainless-steel cryostat pipe is also compared with the calculated one.
    IEEE Transactions on Applied Superconductivity 06/2015; 25(3):1-5. DOI:10.1109/TASC.2014.2366996 · 1.24 Impact Factor
  • S Fujita · M Daibo · M Igarashi · R Kikutake · K Kakimoto · Y Iijima · M Itoh · T Saitoh ·
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    ABSTRACT: REBa2Cu3Oy, (RE : rare earth elements, RE123) coated conductors are expected to show high performance in superconducting applications, due to their high mechanical strength and high current density in magnetic fields. Fujikura has developed ion-beam-assisted-deposition (IBAD) and pulsed-laser-deposition (PLD) technique, and today we routinely manufacture coated conductors with length over 500 m and Ic over 500 A/cm-width at 77 K, self field. We have also been able to fabricate long conductors with higher Ic by thickening RE123 layer. Although Ic performances at 77 K, self field are important, but performances in magnetic fields at lower temperatures below 77 K are more important for coil applications. In this work, we evaluated coated conductors with thick RE123 layer in magnetic fields at low temperatures. All samples are fabricated with long length. We measured samples by four-probe transport method at wide temperature range from 77 K to 10 K by using cryo-cooled cryostat. A conductor with 5.5 μm thick RE123 exhibits high Ic values of 937 A/cm-width at 77 K, self field, 637 A/cm-width at 50 K, 5T and 976 A/cm-width at 40 K, 5T.
    Journal of Physics Conference Series 05/2014; 507(2):022007. DOI:10.1088/1742-6596/507/2/022007
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    ABSTRACT: Since the development of the 18T cryogen-free superconducting magnet (18T-CSM) at the High Field Laboratory for Superconducting Materials (HFLSM), IMR, Tohoku University, it has been routinely utilized for the various high field researches such as the in-field materials processing and so on. After the Great East Japan Disaster, however, the 18T-CSM is under the repairing due to the serious damages of the system. At this time, a part of the middle Nb3Sn section coil and the Bi2223 inner most coil were renewed. The bronze-route Nb3Sn coil with a low ac-loss was adopted instead of the previous internal-Sn Nb3Sn coil for the reduction of the heat-generation during a field ramping. The new Bi2223 coil will generate the central field of 4.5 T under the background field of 15.5 T by the LTS outer coils, although the previous Bi2223 coil generated 2.5 T. Hence the 18T-CSM was successfully upgraded to the 20T-CSM. In addition to the Bi2223 insert, the Gd123 insert coil is being constructed as well. When the Gd123 insert coil is installed instead of the Bi2223 coil, it will be upgraded to the 22T-CSM from the 20T-CSM.
    Joint Conference of the Transactions of the Cryogenic Engineering; 01/2014
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    ABSTRACT: The decay time of induced radioactivity in V3Ga is remarkably shorter than in Nb-based compounds, making the V3Ga compound as one of the candidate and suitable superconducting magnet materials for the future nuclear fusion system. In order to improve the superconducting properties of V3Ga multifilamentary wires, we investigated high Ga content TiGa3 compound with various Cu addition as the Ga source material. The Cu additions into TiGa3 compounds were 10, 30, and 50 wt.%, respectively. The volume fraction of V3Ga phase was increased with increasing of Cu addition. We confirmed that Cu addition into TiGa3 compound promoted the formation of the V3Ga phase. The optimum Cu addition into TiGa3 compound on superconducting properties was obtained to be 30 wt.%, and H-c2 value of the 30 wt.% Cu sample was estimated to be above 24 T. This value was 3 T higher than conventional "Bronzed route" processed V3Ga wires.
    IEEE Transactions on Applied Superconductivity 06/2013; 23(3). DOI:10.1109/TASC.2013.2245933 · 1.24 Impact Factor
  • M. Daibo · S. Fujita · H. Hidaka · M. Haraguchi · Y. Iijima · M. Itoh · T. Saitoh ·
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    ABSTRACT: REBCO coated conductors having a performance greater than 300 A/cm at 77 K have been developed for superconducting applications. The conduction-cooled coils fabricated using REBCO coated conductors are expected to have the high performance because the specific heats of the constituent materials increases greatly with the operating temperature. From the point of view of the coil design using REBCO coated conductors, we must consider the critical current versus the magnetic field characteristics and their temperature dependence.In this study, we fabricated the two-layer stacked racetrack coil whose outer diameter was 92 × 172 mm with 56 turns. The coil used the REBCO coated conductor, whose critical current was around 200 A/5 mm at 77 K self field, manufactured by Fujikura Ltd. We compared with the calculated and measured the voltage distribution of one racetrack coil, which was attached with voltage taps each turn, at 77 K in self field. We investigated the Ic of the two-layer coil at 65 K and 50 K under conduction-cooled conditions. The Ic values of the two-layer coil in self field using a criterion of 10−7 V/cm were achieved 220 A at 65 K and 386 A at 50 K, which the central magnetic fields were 0.13 T at 65 K and 0.23 T at 50 K, respectively.
    Physica C Superconductivity 01/2013; 484:292–294. DOI:10.1016/j.physc.2012.03.020 · 0.94 Impact Factor
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    ABSTRACT: We have investigated electric field criterion of in-plane critical current density in a coated conductor characterized by scanning Hall-probe microscopy (SHPM). From remanent field distribution and its relaxation measurements, we could obtain critical current distribution and induced electric field simultaneously by considering the Biot-Savart law and the Faraday’s law, respectively. These results lead us to evaluate a distribution of local critical current density and the corresponding criterion of electric field. As a result, it was found that the electric field criterion for the SHPM analysis was several orders lower than that used in the conventional 4-probe resistive method. However, the data point obtained by the SHPM shows good agreement with E–J curve analytically extended from the measurements by the 4-probe method. This means that we could characterize in-plane distribution of critical current density in a coated conductor at an electric field criterion quantitatively by this method in a nondestructive manner. These findings will be very important information since the uniformity of local critical current density in a coated conductor at extremely low electric fields is a key issue (1) especially for DC applications, (2) for quality control of coated conductors, and (3) for the standardization of the characterization of critical current among different methods.
    Physica C Superconductivity 01/2013; 484:139–141. DOI:10.1016/j.physc.2012.03.067 · 0.94 Impact Factor
  • T. Takeuchi · K. Tsuchiya · M. Saeda · N. Banno · A. Kikuchi · Y. Iijima ·
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    ABSTRACT: Observations of fractured cross sections, which are frequently used to determine the grain size distribution in Nb<sub>3</sub>Sn, cannot be performed for Nb<sub>3</sub>Al since transgranular fracture is the dominant fracture mode. Instead, we have evaluated the grain size of Nb<sub>3</sub>Al using electron backscatter diffraction (EBSD). To check the validity of EBSD analysis for A15 grain structures, bronze-route Nb<sub>3</sub>Sn filaments were also examined by EBSD. The deformation-and-transformation of bcc supersaturated-solid solution Nb(Al)<sub>ss</sub> was found not only to homogenize and refine the grain size of the resultant Nb<sub>3</sub>Al but also to increase a ratio of high angle grain boundaries to low angle grain boundaries. The texture studies were made by pole figure works: the Nb(Al)<sub>ss</sub> retains a 〈110〉 fibrous texture as well as the filament barrier (Nb, Ta) does. The transformed Nb<sub>3</sub>Al also has the weak 〈110〉 fibrous texture, whereas Nb<sub>3</sub>Sn has almost never texture. A clear relationship between Jc and the inverse of grain size was not observed.
    IEEE Transactions on Applied Superconductivity 07/2011; 21(3-21):2541 - 2545. DOI:10.1109/TASC.2010.2083625 · 1.24 Impact Factor
  • M. Daibo · S. Fujita · M. Haraguchi · Y. Iijima · T. Saitoh ·
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    ABSTRACT: The quench characteristics, particularly the normal-zone propagation and increase in hot-spot temperature, of REBa<sub>2</sub>Cu<sub>3</sub>O<sub>x</sub> (REBCO) coated conductors are important issues for safe operation in the superconducting applications. Although experimental data on the quench characteristics of REBCO coated conductors have been reported only limited data is available specifically on REBCO coated conductors laminated with Cu tape of thickness no less than 0.1 mm, which are expected to be used for high-current operation in future superconducting applications. Here we reported experimental measurements of the normal-zone propagation velocity (NZPV) in REBCO coated conductors laminated with Cu tape of 0.1 mm thickness at 77, 65 and 50 K in a background magnetic field. We also compared these results with the NZPV at 77 K of REBCO coated conductors laminated with Cu stabilizer tape of thickness 0.05 and 0.3 mm.
    IEEE Transactions on Applied Superconductivity 07/2011; 21(3-21):2428 - 2431. DOI:10.1109/TASC.2011.2105454 · 1.24 Impact Factor
  • Y. Iijima · M. Kimura · T. Saitoh ·
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    ABSTRACT: Biaxially aligned film growth by dual-ion-beam sputtering methods were studied for fluorite type (Zr0.85Y0.15O1.93(YSZ), Hf0.74Yb0.26O1.87, CeO2), pyrochlore type (Zr2Sm2O7), and rare-earth C type (Y2O3, Sm2O3) oxides on polycrystalline Ni-based alloy substrates. Cube-textured (all axes aligned with a 〈100〉 axis substrate normal) films were obtained for fluorite and pyrochlore ones by low energy (<300 eV) ion bombardment at low temperatures (<300 °C). Besides, cube textured Y2O3 films were obtained in far narrower conditions with a quite low energy (150 eV)-ion bombardment at the temperature of 300 °C. The assisting ion energy dependence was discussed in connection with lattice energies for these oxide crystals.
    MRS Online Proceeding Library 01/2011; 587. DOI:10.1557/PROC-587-O2.3
  • T Takeuchi · K Tsuchiya · M Saeda · N Banno · A Kikuchi · Y Iijima ·
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    ABSTRACT: To enhance the non-Cu critical current density Jc at 15 T and 4.2 K (1000 A mm − 2 at present) we have endeavoured to refine the grain size of rapid heating, quenching and transformation (RHQT)-processed Nb3Al. In the present study, the grain boundary structures of RHQT-processed Nb3Al were examined by electron backscatter diffraction (EBSD) because transgranular fracture prevents the observation of fractured cross sections of Nb3Al to statistically determine the grain size. The grain size distributions of body-centred-cubic supersaturated-solid-solution Nb(Al)ss and A15 Nb3Al filaments were measured for grains misoriented by more than 2°, 5° and 15°. A mixed grain structure, which consists of a few large grains (>25 µm) and many small grains (<1 µm), was observed for an Nb3Al filament that had been transformed from non-deformed Nb(Al)ss. Plastic deformation that had been made between the rapid heating and quenching steps and the transformation step apparently homogenized the grain size distribution and then reduced the average grain size. The misorientation angle distributions of Nb(Al)ss and Nb3Al were also measured and compared with each other. A clear relationship between the Jc and the inverse grain size was not confirmed for the RHQT Nb3Al conductors examined in the present study, which indicates the importance of making a filament compositionally homogeneous to obtain a high Jc.
    Superconductor Science and Technology 10/2010; 23(12):125001. DOI:10.1088/0953-2048/23/12/125001 · 2.33 Impact Factor
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    ABSTRACT: Increase of production rate and improvement of quality for RE123 coated conductors have been tried. In-plane texturing of MgO was attempted by the IBAD system with the world largest ion source. As a result of optimizing condition in large deposition area, the dramatically high throughput of 1000 m / h was realized to obtain the IBAD-MgO with Δ < 10°. Furthermore, simple buffer structure was demonstrated. Well textured CeO2 layer with Δ of around 4° was obtained by directly deposited on IBAD-MgO layer in spite of large lattice mismatch of 28% between CeO2 and MgO. Several over 100 m buffer substrates with the architecture of / PLD-CeO2 (60 m / h) / IBAD-MgO (333~1000 m / h) / Y2O3 (500 m / h) / Al2O3 (150 m / h) / Hastelloy / were already prepared. On these production substrates, GdBCO layer was deposited by the large PLD system at high throughput. The 260 m long GdBCO tape with Ic > 600 A except some locations was obtained at the throughput of 15 m / h. In addition to the speed-up, the very high Ic of 1040 A was also achieved by the hot-wall heating PLD system.
    Journal of Physics Conference Series 07/2010; 234(2):022016. DOI:10.1088/1742-6596/234/2/022016
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    ABSTRACT: Rapid heating/quenching and transformation (RHQT)-processed Nb3Al wires possess better strain tolerance than Nb3Sn wires and exhibit similar high-field properties. Therefore, Nb3Al wires might be promising candidates for use in future high-field accelerator magnets. For this reason, we have been developing RHQT-processed Nb3Al wires for a number of years. During this development, magnetization measurements on several samples have been carried out as a function of either temperature or the magnetic field. This paper presents some of the results of the magnetization measurements performed.
    Journal of Physics Conference Series 07/2010; 234(2):022040. DOI:10.1088/1742-6596/234/2/022040
  • A Kikuchi · Y Iijima · T Takeuchi · Y. Hishinuma ·

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    ABSTRACT: In Japan we started a national project to develop a 66/6.9 kV–20 MVA transformer with REBCO superconducting tapes in 2006. This paper gives an overview of progress of the development of superconducting transformers in Japan and also describes the fundamental technologies studied before now to realize a 66/6.9 kV–20 MVA transformer as follows. To reduce the ac loss in REBCO superconducting thin tapes, authors proposed a new method different from the conventional technique of reducing the ac loss in superconducting multifilamentary wires. It consists of scribing process into a multifilamentary structure by laser or chemical etching, and a special winding process. Making a multilayered solenoidal coil with laser-scribed REBCO tapes, we verified the ac loss reduction in proportion to a filament width even in coil configuration. In addition, to realize a current capacity more than the rated secondary current of 2.4 kA, we first investigated the workability of REBCO tapes in the actual winding process with forming a transposed parallel conductor, where REBCO tapes were bent edgewise at transposing points. Making a test coil of a 24-strand parallel conductor, we verified no degradation of the critical current and nearly uniform current distribution among the tapes. The result suggests the applicability of the method of enhancing the current capacity by forming a parallel conductor with REBCO tapes. Further, to realize the dielectric strength regulated for the Japanese standards, i.e. lightning impulse withstand level of 350 kV and excess ac voltage of 140 kV, we made test coils and carried out dielectric breakdown tests. As a result, we got hold of the required insulation distance at the important points from the viewpoint of insulation design.
    Physica C Superconductivity 10/2009; 469(15-20):1726-1732. DOI:10.1016/j.physc.2009.05.246 · 0.94 Impact Factor
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    ABSTRACT: We have visualized non-uniform current flow in RE123 coated conductors by using a scanning Hall-probe magnetic microscopy (SHPM). Newly developed SHPM system allows us to measure two-dimensional magnetic field distribution with high spatial resolution in micro-meter scale. Corresponding current density distribution can be obtained from the magnetic field image by solving inverted Biot–Savart’s law. One of the most important advantages of the present system is to visualize the current density distribution in practical high transport current and also in wide scanning area. For example, the system has current leads with large capacity up to 500 A, and the operating distance can be 15 cm by 15 cm with a micro-meter step distance. Using the SHPM system, we have successfully visualized current density distributions in the coated conductor, and clarified different kinds of non-uniform current flow. Those insights are very useful to identify local defects as well as non-uniform tape quality. These results indicate that the SHPM system is a powerful diagnostic tool not only to observe spatial inhomogeneities of transport property but also to understand their reason in practical coated conductors.
    Physica C Superconductivity 10/2009; 469(15-20):1450-1453. DOI:10.1016/j.physc.2009.05.060 · 0.94 Impact Factor
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    ABSTRACT: One of the programs in the Ministry of Economy and Trade and Industry (METI) project regarding R & D on YBCO conductor is to evaluate the applicability of the developed conductor toward several applications. This paper focuses on a fault current limiter (FCL) as one of the expected power applications. YBCO tape conductors with ion beam assisted deposition (IBAD) substrate are used in this work. In order to obtain high resistance of the conductor, which is preferable to an FCL, the thickness of the protecting layer made of silver was decreased as possible. Then high-resistive metal stabilizing layer is attached on the silver layer to improve stability. Obtaining the relevant current limiting performance on short sample experiments, model coils were developed to aim the 6.6 kV-class FCL. Short circuit experiments were implemented with a short circuit generator. The coil successfully restricted the short circuit current over 17 kA to about 700 A by the applied voltage of 3.8 kV, which is nominal phase-to-ground voltage. The experimental results show good agreement with computer analyses and show promising toward the application.
    Physica C Superconductivity 09/2008; 468(15-20):2046-2049. DOI:10.1016/j.physc.2008.05.123 · 0.94 Impact Factor
  • S Hanyu · T Miura · Y Iijima · M Igarashi · Y Hanada · H Fuji · K Kakimoto · T Kato · T Hirayama · T Saitoh ·
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    ABSTRACT: We fabricated a long-length GdBCO(GdBa2Cu3O7-δ) coated conductor by the ion-beam assisted deposition (IBAD) and the pulsed laser deposition (PLD) methods. The GdBCO tape was over 400 m in length with 1.5-2.0 MA/cm2 of the critical density. The critical currents of the tape were over "304.8 A/cm" along 368 m in length. So we have achieved "Ic × L = 112,116 Am". For the IBAD process, we have already developed 500 m-length IBAD-Gd2Zr2O7 (IBAD-GZO) tapes with highly aligned in-plane texture, and continuously fabricate 250 m-length tapes at a rate of 0.5~1 km/month. In addition, we have also developed a new type template for the IBAD-GZO, to enable the production rate fast. Structure of the template is IBAD-GZO/IBAD-MgO/Y2O3. It is note that MgO (111) is parallel to the substrate normal and three fold symmetry. For this structure, the film thickness of the IBAD-GZO could lessen from 1.2 μm to 0.3 μm. By the new IBAD buffer layer, a production rate is expected to be over 30 m/h.
    Journal of Physics Conference Series 03/2008; 97(1):012273. DOI:10.1088/1742-6596/97/1/012273
  • T Takeuchi · H Takigawa · M Nakagawa · N Banno · K Inoue · Y Iijima · A Kikuchi ·
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    ABSTRACT: We have succeeded in making a superconducting Nb–Zr and V–Ti alloy multifilament wire using the diffusion reaction between constituent pure-metal subelements, which can omit the melt-and-casting step and may reduce the fabrication cost. A third element addition was also performed by replacing the constituent subelements with the third pure-metal subelement in the monofilament; Nb–Zr–V, Nb–Zr–Ti and V–Ti–Ta. Three kinds of heat treatment were investigated; (1) an alloying heat treatment (HTalloy) which is carried out at the final size ('fs-HTalloy '), (2) HTalloy is followed by cold-working (W) down to the final size ('HTalloy+W '), and (3) an intermediate precipitation heat treatment (HTprec) is carried out during the W stage coming after the HTalloy stage ('HTalloy+W+HTprec+W' ). The 'HTalloy+W+HTprec+W' treatment was found to be most effective in enhancing the critical current densities for both Nb–68 at.% Zr and V–60 at.% Ti–9 at.% Ta alloys, despite the HTprec treatment having slightly degraded the critical magnetic field.
    Superconductor Science and Technology 01/2008; 21(2):025004. DOI:10.1088/0953-2048/21/02/025004 · 2.33 Impact Factor
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    ABSTRACT: Recent studies of RHQ-processed Nb<sub>3</sub>Al wires for future accelerator magnets are presented and discussed. Test wires were prepared with different fabrication parameters, such as the Nb matrix ratio, RHQ current, area reduction ratio of the wire after an RHQ treatment and the 2nd heat treatment condition. Measurements of the critical current density (J<sub>c</sub>) and n-value have been performed during the past several years. Recently, we performed the critical temperature (T<sub>c</sub>) measurement, and the relationship between J<sub>c</sub> and T<sub>c</sub> was investigated by an RHQ treatment, a 2nd heat treatment, the Nb matrix ratio, and the area reduction effect.
    IEEE Transactions on Applied Superconductivity 07/2007; 17(2-17):2693 - 2696. DOI:10.1109/TASC.2007.899006 · 1.24 Impact Factor

Publication Stats

947 Citations
61.32 Total Impact Points


  • 1993-2014
    • Fujikura Ltd.
      Edo, Tōkyō, Japan
  • 2004-2010
    • National Institute for Materials Science
      Tsukuba, Ibaraki, Japan
  • 2001
    • Central Research Institute of Electric Power Industry
      Edo, Tōkyō, Japan
  • 1989-1999
    • Tsukuba Research Institute
      Edo, Tōkyō, Japan
  • 1983
    • Furukawa Electric
      Edo, Tokyo, Japan