F. Sumiyoshi

National Institute for Fusion Science, Tokitsu-chō, Gifu, Japan

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Publications (94)96.74 Total impact

  • A. Kawagoe, H. Moribe, K. Kakiyama, F. Sumiyoshi
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    ABSTRACT: We have proposed a new method for detecting unusual local conditions in a high-temperature superconducting coil. In this method, two kinds of pick up coils for measuring electric fields and magnetic fields are used to obtain Poynting's vectors around the coil. This is a noncontact method using pick-up coils around the vessel for cooling the coil. The method has the following benefits: safe detection, easy handling, high sensitivity, and high usability. The purpose of this paper is to clarify the relation of measured signals to the conditions of the windings. When a temperature rise has been produced locally in the Bi-2223 solenoidal coil, Poynting's vectors around the coil and the temperature of windings were measured. It was found that the measured signals rapidly decrease as the temperature of the winding achieved a critical level, making this a reliable method to estimate the conditions in the windings.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):9000804-9000804. · 1.20 Impact Factor
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    ABSTRACT: The MgB<sub>2</sub> coil wound with a parallel conductor composed of two MgB<sub>2</sub> tapes with insulation has been developed. The tape is obtained by the rolling process from the round wire which is fabricated by in-situ method. The performances of tapes, such as critical current density and ac losses, are higher than that of round wires in case that the transverse magnetic fields are applied to the tape in direction of the parallel to the flat face of the tape. We proposed as a candidate of applying the tape to a conductor with large current capacity that the parallel conductor is composed of insulated tapes. We fabricated a tape with aspect ratio of two from a round wire with diameter of 0.8 mm as a strand for the conductor. The coil is composed of two coils that are jointed each other in series. At the joint, two strands are transposed to be identical the inductances of two strands. The inner and outer diameters of the coil are 65 mm and 107 mm, respectively. The length of the coil is 53 mm. The total turn number is 540 turn. The magnetic flux density at the center in the coil is 1.31 T when the transport current is 200 A. In this paper, the design and the test results of the MgB<sub>2</sub> coil wound with the conductor are shown and the critical current properties and ac loss properties of the coil are discussed.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
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    ABSTRACT: It was theoretically confirmed that improvement of superconducting-coil performance can be obtained by making optimum use of multifilamentary tapes with high aspect-ratio cross-sections. Superconducting tapes, such as NbTi and MgB2 multifilamentary tapes, are known to have anisotropic electromagnetic properties, i.e., critical current densities and ac losses; under external transverse magnetic fields which are parallel to the tape face, the critical current density is higher than that of the multifilamentary round wire, but the ac loss is lower. For tapes with a high aspect-ratio cross-section, the anisotropic properties are still more remarkable, and therefore it is predicted that such a tape with superior electromagnetic properties will prove valuable as the windings of high performance coils for practical applications. In this paper, some examples of coil arrangements such as single or plural solenoid coil systems are shown in order to highlight the usefulness of this superior tape performance. The effect of the high aspect-ratio of tape cross-section on the electromagnetic coil performance was also discussed, taking the cooling condition of coil windings into account.
    Journal of Physics Conference Series 07/2010; 234(2):022038.
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    ABSTRACT: We have proposed MgB<sub>2</sub> multifilamentary tapes with high critical current densities and low ac losses under external magnetic fields which is parallel to the tape face. The purpose of this proposal is to develop the MgB<sub>2</sub> new conductors composed of plural tapes as windings of superconducting coils with both large current capacities and low losses for fusion reactors, superconducting magnetic energy storage systems, and so on. Our MgB<sub>2</sub> multifilamentary tapes are fabricated by rolling process from round wires. The tapes are fabricated by using in-situ method. The purpose of this paper is to clarify the effects of deformation to tape shape on the electromagnetic properties of MgB<sub>2</sub> filaments in multifilamentary wires. For the purpose, measurements of both critical currents and magnetizations have been carried out on MgB<sub>2</sub> fine single filament wires which have simulated a filament in multifilamentary wires. Measurements on wires with large diameter have been also carried out, in order to clarify the effect of diameters of original round wires. We prepared pure and SiC-added MgB<sub>2</sub>/Nb/Cu composite wires as the original round wires before rolling process. The diameters of round wires have been varied and then the aspect ratios of tapes have been varied. The observed critical current densities of the tapes are about 7 times larger than that of the original round wire at a maximum. The ratios of J<sub>c</sub> of wires to tapes don't have dependence of the diameter of the original round wire. In addition, the results of measurements of magnetizations have shown that magnetization losses in MgB<sub>2</sub> tapes decrease to 1/3 compared with original round wires.
    IEEE Transactions on Applied Superconductivity 07/2010; · 1.20 Impact Factor
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    ABSTRACT: We have developed a new monitoring system to detect an unusual event in the superconducting coils without direct contact on the coils, using Poynting’s vector method. In this system, the potential leads and pickup coils are set around the superconducting coils to measure local electric and magnetic fields, respectively. By measuring the sets of magnetic and electric fields, the Poynting’s vectors around the coil can be obtained. An unusual event in the coil can be detected as the result of the change of the Poynting’s vector. This system has no risk of the voltage breakdown which may happen with the balance voltage method, because there is no need of direct contacts on the coil windings. In a previous paper, we have demonstrated that our system can detect the normal transitions in the Bi-2223 coil without direct contact on the coil windings by using a small test system. For our system to be applied to practical devices, it is necessary for the early detection of an unusual event in the coils to be able to detect local normal transitions in the coils. The signal voltages of the small sensors to measure local magnetic and electric fields are small. Although the increase in signals of the pickup coils is attained easily by an increase in the number of turns of the pickup coils, an increase in the signals of the potential lead is not easily attained. In this paper, a new method to amplify the signal of local electric fields around the coil is proposed. The validity of the method has been confirmed by measuring local electric fields around the Bi-2223 coil.
    Physica C Superconductivity 01/2010; 470(20):1860-1864. · 0.72 Impact Factor
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    ABSTRACT: A new quench monitoring system by using the Poynting vector method was proposed. This new system can indirectly detect normal transitions which are suddenly induced during an operation of superconducting coils. In this system, the superconducting coil is surrounded by the thin metallic cylinder composed of several pieces, where the cylinder is electrically insulated from the coil; potential leads to measure local electric fields are directly attached to this cylinder surface and pickup coils to measure local magnetic fields are put on the surface. The Poynting vector distribution around the coil can be obtained by using many sets of both the potential lead and the pickup coil. Since sudden changes of energy flow profiles around the superconducting coil are induced in the event of local normal transitions of the coil winding, such an event of coils can be detected by the change of the Poynting vector. This system has no risk of the destructive voltage breakdown which may happen in case of the existing balance voltage method, because there is no need of direct contacts on the coil windings. In addition, this method is expected to be higher reliability and sensitivity than the acoustic emission method. A demonstration test was carried out of monitoring the quench for the Bi-2223 coil partially immersed in liquid nitrogen, and a sign of normal transitions before the quench was successfully detected by this method.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: MgB<sub>2</sub> multifilamentary tapes with 6 twisted filaments were fabricated and it was experimentally proven that both an increase in critical currents and a decrease in ac losses in the tapes due to deformation of the tapes with high aspect ratio can be simultaneously attained. This will improve the performance of MgB<sub>2</sub> wires for the new conductors as windings of superconducting coils with both low losses and high stability for fusion reactors, superconducting magnetic energy storage systems, and so on. There are three kinds of prepared samples in which one sample is a round wire of 1.02 mm in diameter and other samples are tapes obtained by the rolling process from the round wire. The aspect ratios of these tapes are 3.3 and 6.6. These wires are composed of MgB<sub>2</sub>/Nb/CuNi . The 6 filaments are twisted with twist pitches of 50 mm. The measurements of critical currents and coupling losses were carried out at 4.2 K. The observed critical current densities of the tapes are two times larger than that of the round wire under the external magnetic fields of 2 T to 7 T in a direction parallel to the flat faces of the tapes. The observed coupling losses in the tape with aspect ratio of 6.6 were 1/10 smaller than that of the round wires, where the parallel magnetic fields were applied to the flat faces of the tapes.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: The development study of a 1 MJ conduction-cooled low temperature superconducting (LTS) pulse coil used for a 1 MW, 1 s UPS-SMES is summarized. We have developed a conduction-cooled LTS pulse coil as a key technology for the UPS-SMES. The AC loss reduction and the high stability are required for the SC conductor for a LTS pulse coil because of a limited cooling capacity of 4 K cryocooler. The conductor of a NbTi/Cu compacted strand cable extruded with an aluminum was designed to have the anisotropic AC loss properties to minimize the coupling loss. The coil was wound, utilizing a specially developed automatic winding machine which enables an innovative twist-winding method. The Dyneema FRP (DFRP) spacers and the Litz wires (braided wires of insulated copper strands) were inserted in each layer in order to enhance the heat transfer in the coil windings. The coil was installed in the test cryostat and was connected to three GM cryocoolers, which have a total cooling capacity of 4.5 W at 4 K and 240 W at 50 K. The coil was cooled conductively without liquid helium by attaching the end of the Litz wires directly to the cold heads of the cryocoolers. The cooling and excitation test of the 1 MJ coil has been done successfully. The test results validated the high performance of the conduction-cooled LTS pulse coil, because the high thermal diffusivity resulted in the rapid temperature stabilization in the coil.
    IEEE Transactions on Applied Superconductivity 07/2009; · 1.20 Impact Factor
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    ABSTRACT: AC losses in the conduction-cooled low temperature superconducting (LTS) pulse coil with stored energy of 1 MJ are estimated. The 1 MJ coil is a superconducting pulse coil for 1 MW, 1 sec UPS-SMES. UPS-SMES is an uninterruptible power supply (UPS) with superconducting magnetic energy storage (SMES) for protection of production lines of an industrial plant or large-scale experimental devices such as a fusion device, from a momentary voltage drop and an instant power failure. The winding conductor for the 1 MJ coil is a NbTi/Cu Rutherford cable, which is extruded with aluminum. The 1 MJ coil was wound by a new twist winding method. A 1 MJ coil was fabricated and cooling and excitation tests were carried out. In this paper, two methods to estimate ac losses in conduction-cooled LTS coils are proposed. One method estimates ac losses in the coil under steady-state conditions. The other method estimates ac losses in the coil under transient-state conditions. For estimation of ac losses in the 1 MJ coil, measurement of temperature in the coil during tests and thermal analysis using the two-dimensional finite element method are compared. These procedures clarified that the 1 MJ coil has low losses.
    IEEE Transactions on Applied Superconductivity 07/2008; · 1.20 Impact Factor
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    ABSTRACT: In order to realize HTS power devices with high performances, it is important to evaluate the characteristics of HTS conductors theoretically and experimentally. In the experimental evaluation, an ac power supply with a large current capacity and few ripples is necessary. To this end, we developed a compact HTS current transformer for evaluating the characteristics of HTS conductors. This transformer is wound in an elliptical shape with using Bi-2223 tape. The secondary current of the current transformer can be induced at about 1 kA at 77 K when the primary current is 40 A. The transformer was fabricated very compactly, and the externals size is 70 mm in the diameter, and 110 mm in length. To confirm the practicality of the transformer, the current was actually energized to an HTS conductor composed of 16 Bi-2223 tapes. The results of the performance test of the current transformer and the method of increasing the current capacity of the current transformer are also discussed.
    IEEE Transactions on Applied Superconductivity 07/2008; · 1.20 Impact Factor
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    ABSTRACT: It is important to evaluate the characteristics of the current distributions in the HTS tapes and conductors in order to realize HTS power devices. In this study, we have developed a simple measurement method to evaluate the current distributions in HTS tapes. In this method, the current distributions are indirectly found from the results of the field distributions measured by an array of precise pickup coils arranged on the upper surface of the sample tape. To confirm the accuracy and sensitivity of this method, current distributions in a test conductor made of copper wires are measured. Numerical and measured current distributions are compared, and it is found that our method is accurate enough to measure the current distributions in HTS tapes. Using this method, the current distributions in a multifilamentary Ag-alloy sheathed Bi-2223 tape are measured at 77 K. In addition, the effectiveness of our method as detection method of degradation areas of the HTS tapes is examined.
    Physica C Superconductivity 01/2008; 468:1734-1738. · 0.72 Impact Factor
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    ABSTRACT: We have strategically promoted R&D activity for the development of elemental technologies in order to put into practical HTS power transformers applying YBa2Cu3O7 (YBCO) coated conductors, focused on AC loss reduction in HTS coils. This paper shows AC loss reduction in model coils of YBCO tapes divided into five filaments by laser ablation. At first experiment, magnetization loss of YBCO tape with five filaments and YBCO tape with non-divided were firstly measured using a pick-up coil technology. Then, AC loss measurement is performed using two types of model coils of YBCO tapes with five filaments and non-divided, by two different technologies: an electric technique (i.e. 4-probe) and a calorimetric technique (i.e. boil-off). The results of the experiment show that the AC loss in the model coil of YBCO tapes with five filaments was reduced to one-fifth when compared with model coil of YBCO tapes with non-divided.
    Physica C Superconductivity 01/2008; 468:1731-1733. · 0.72 Impact Factor
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    ABSTRACT: Several kinds of NbTi/Cu multifilamentary tapes with high aspect-ratio cross-sections were fabricated in order to develop new conductors used for windings of conduction-cooled LTS pulse- coils with both low ac losses and high stability. These tapes were obtained by the cold rolling process from normal multifilamentary wires. For the edge-on transverse magnetic field at 4.2 K, about 20% increases in critical current densities at 6 T were observed for the tape with the highest aspect ratio of 7.4, and its hysteresis losses estimated from the observed magnetization were reduced to approximately one-half of those in the original wire. In this edge-on filed condition, the observed coupling losses in the tape were also decreased to about 1/17 times as large as those in the original wire. These experimental results showed that the NbTi/Cu multifilamentary tape had strong anisotropy of electromagnetic properties such as critical currents, hysteresis losses, and coupling losses and that good performances were obtained for edge-on transverse magnetic fields.
    IEEE Transactions on Applied Superconductivity 07/2007; · 1.20 Impact Factor
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    ABSTRACT: A 1 MW, 1 s UPS-SMES is being developed for a protection from a momentary voltage drop and an instant power failure. As a key technology of the UPS-SMES, we developed a prototype LTS pulse coil with a stored energy of 100 kJ and conducted cooling and excitation tests in 2005. The operation test of the prototype UPS-SMES using this 100 kJ coil with power converters have been performed in 2006. A 1 MJ coil was designed before the fabrication of the 100 kJ prototype coil. The superconductor, the electric insulation technique, the winding method, and the cooling structure used for the 100 kJ coil were based upon the 1 MJ coil design. The successful performance test results of the prototype 100 kJ coil validated the design concept and fabrication technique of the 1 MJ coil. According to the achievement of the prototype 100 kJ UPS-SMES, the 1 MJ conduction-cooled LTS pulse coil has been fabricated successfully. The successful experimental results of the 100 kJ prototype coil with power converters and the fabrication procedure of the 1 MJ full size coil are described.
    IEEE Transactions on Applied Superconductivity 07/2007; · 1.20 Impact Factor
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    ABSTRACT: The stability margin of a conduction-cooled LTS pulse coil with stored energy of 1 MJ, which is used for UPS-SMES as protection from momentary voltage drops, is estimated from thermal analyses using the two-dimensional finite elementary method. How much the 1 MJ coil is able to be downsized is discussed. The winding conductor of this coil is a NbTi/Cu Rutherford cable, which is extruded with aluminum. Dyneema FRP and Litz wires are used as the spacers of this coil. In the design of this 1 MJ coil, the effects of spacers were neglected. In order to estimate the stability margin, thermal analyses was carried out by taking into account the thermal effects of spacers, for the coil during overload operation. And it was checked whether the maximum temperature The results showed that the 1 MJ coil has a large stability margin of 8 times the rated ac loss. In addition, new coils with a stability margin of about two times were designed. Possibilities for reducing the size and the cost of a 1 MJ LTS pulse coil are also shown.
    IEEE Transactions on Applied Superconductivity 07/2007; · 1.20 Impact Factor
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    ABSTRACT: The nitrogen boil-off method, which is categorized as one of the calorimetric methods, has been developed as a practical method for measuring AC losses in high temperature superconducting (HTS) coils. The boil-off method offers direct and convenient measurement compared to the electric method. The measurement sensitivity of about 0.5 W was confirmed by the improvement of sample vessel structure and the control of the heater power. This paper reports the results of a comparison of the AC losses in superconducting coils using YBCO tapes measured with the boil-off method and those obtained by the electric method and by analysis.
    Physica C Superconductivity 01/2007; · 0.72 Impact Factor
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    ABSTRACT: For a SMES to protect the whole facility from momentaly voltage drop, a helium free superconducting pulse coil using conduction cooling is developed. Also short time power converters and a high-speed voltage drop detector for a 1 MJ class SMES are designed. To confirm the design of components, a 100 kJ class demo system is constricted tested. After that the half part of 1 MJ SMES is constricted for operation tests.
    01/2007;
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    H. Okamoto, F. Sumiyoshi, K. Miyoshi, Y. Suzuki
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    ABSTRACT: We have developed a novel apparatus for applying a nitrogen boil-off method as a mean of making calorimetric measurements and allowing for simple measuring and evaluating of AC losses in HTS coils at liquid nitrogen temperature. With the ability to measure AC loss generated in superconductors directly, this method produces more reliable data than that obtained by general, electro-magnetic measurements. A sensitivity of about 0.1 W was achieved by improving sensitivity in measuring gas evaporation via the following three steps: (1) use of nonmetallic vessel, heat-insulated housing in which the sample is located; (2) optimization for sample vessel thickness and tube size; and (3) stabilization of evaporating gas emitted by the heater. It is widely expected that the proposed apparatus may be used for individual measurement of the magnetization loss and the transport current loss in HTS coils, as well as their total losses, in addition to the AC loss in irregularly shaped samples
    IEEE Transactions on Applied Superconductivity 07/2006; · 1.20 Impact Factor
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    ABSTRACT: Inter-strand coupling loss measurements were carried out in liquid helium for Bi-2212 Rutherford cables composed of 30 non-twisted strands. Short, straight samples composed of three stuck cables were set in a uniform field space inside the NbTi magnet of race-track and split type. Frequency characteristics of coupling losses were observed for transverse ac magnetic field, both perpendicular and parallel to the flat face of cables. An additional measurement of ac losses was carried out in order to clarify properties of hysteresis losses and intra-strand coupling losses. The obtained effective filament diameter describing the hysteresis loss property indicated that almost all filaments in strands were strongly connected to each other. From both this result and the frequency characteristics of coupling losses for the perpendicular field case, the inter-strand coupling time-constant was given in the order of 10 m. Moreover, the effective contact resistance between crossover strands in the cable was also given in the order of 10<sup>-10</sup> Omegam<sup>2</sup>, which was the same order as that for the NbTi Rutherford cable composed of Cu matrix strands
    IEEE Transactions on Applied Superconductivity 07/2006; · 1.20 Impact Factor
  • Source
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    ABSTRACT: A conduction-cooled low temperature superconducting (LTS) pulse coil has been developed as a key technology for UPS-SMES. We have been developing a 1 MW, 1 s UPS-SMES for a protection from a momentary voltage drop and an instant power failure. A conduction-cooled LTS pulse coil has excellent characteristics, which are adequate for a short-time uninterruptible power supply (UPS). The LTS coil has better cost performance over the HTS coil at present and the conduction cooling has higher reliability and easier operation than the conventional cooling schemes such as pool boiling with liquid helium or forced flow of supercritical helium. To demonstrate the high performances of the LTS pulse coil, we have fabricated a prototype coil with stored energy of 100 kJ and have conducted cooling and excitation tests. The successful performance test results including current shut-off test with a time constant of 1.3 s and repeated excitation of a triangular waveform with high ramp rate are reported
    IEEE Transactions on Applied Superconductivity 07/2006; · 1.20 Impact Factor

Publication Stats

260 Citations
96.74 Total Impact Points

Institutions

  • 1997–2009
    • National Institute for Fusion Science
      Tokitsu-chō, Gifu, Japan
  • 1986–2009
    • Kagoshima University
      • • Department of Electorical and Electronics Engineering
      • • Faculty of Engineering
      Kagosima, Kagoshima, Japan
  • 1994
    • Fukuoka Institute of Technology
      Hukuoka, Fukuoka, Japan
  • 1985
    • Kumamoto University
      Kumamoto, Kumamoto Prefecture, Japan
  • 1978–1984
    • Kyushu University
      • Department of Electronics
      Hukuoka, Fukuoka, Japan