T Takeuchi

Publications (85)100.24 Total impact

• Article: Electron Backscatter Diffraction Analysis on ${hbox {Nb}}_{3}{hbox {Sn}}$ and ${hbox {Nb}}_{3}{hbox {Al}}$ Multifilaments

  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 Nb₃Sn, cannot be performed for Nb₃Al since transgranular fracture is the dominant fracture mode. Instead, we have evaluated the grain size of Nb₃Al using electron backscatter diffraction (EBSD). To check the validity of EBSD analysis for A15 grain structures, bronze-route Nb₃Sn filaments were also examined by EBSD. The deformation-and-transformation of bcc supersaturated-solid solution Nb(Al)_ss was found not only to homogenize and refine the grain size of the resultant Nb₃Al 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)_ss retains a 〈110〉 fibrous texture as well as the filament barrier (Nb, Ta) does. The transformed Nb₃Al also has the weak 〈110〉 fibrous texture, whereas Nb₃Sn has almost never texture. A clear relationship between Jc and the inverse of grain size was not observed.
  IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
• Article: Fabrication of Long-Length Wire by the Metastable Solid-Solution-Strand Restacking Method

  N. Banno, T. Takeuchi, K. Tsuchiya, K. Nakagawa
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  ABSTRACT: This paper describes two subjects, both aimed at the industrialization of Nb₃Al conductors. One is the metastable solid-solution-strand restacking method, which is expected to be a low-cost Cu-stabilization method compared with the electroplating technique. In this paper, we mainly focus on recent efforts toward long-length production. The key point here is an improvement of the contact between the Cu tube and the restacked original strands. The second subject is the first attempt at “constant voltage” control in the continuous rapid-heating and quenching operation for 300-m-class precursor wire. With constant current control, changes in the diameter of the wire lead to variations in power per unit volume, so that the processing temperature changes. With constant voltage control, changes in diameter of the wire do not lead to changes in the power per unit volume, so that the processing temperature does not change and thus the uniformity of the longitudinal performance is improved.
  IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
• Article: Low Critical Current Sensitivity of RHQT ${rm Nb}_{3}{rm Al}$ Wires Under Transverse Compressive Stress Up to 300 MPa

  B. Seeber, A. Ferreira, G. Mondonico, F. Buta, C. Senatore, R. Flukiger, T. Takeuchi
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  ABSTRACT: The critical current of a Nb₃Al wire (RHQT process) with a rectangular cross section of 1.81 × 0.80 × mm² has been measured at 4.2 K under transverse compressive loads at fields between 15 T and 19 T. The same wire (HE2432) was previously used for winding an insert coil at NIMS (coil #B) that generated 4.5 T in a background field of 15 T at 4.2 K. In this work the load is applied perpendicularly to the narrow side of the conductor and the corresponding stresses reach 300 MPa. The critical current stays almost constant up to 150 MPa and shows a flat maximum around 75 MPa. At 300 MPa the critical current is reduced to 93%, 90% and 88% of its stress free value at 15 T, 17 T and 19 T, respectively. This indicates a rather small field dependence and significant degradation being seen only above 200 MPa. Depending on the field, unloading from 300 MPa yields to an almost complete recovery of I_c between 94% and 97% of its initial value, respectively. These observations are compared to the behavior of a Nb₃Sn bronze wire.
  IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
• Article: Electron backscatter diffraction analysis of Nb3Al multifilamentary strands prepared by rapid heating, quenching and transformation annealing

  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. · 2.66 Impact Factor
• Article: Magnetization studies of RHQT-processed Nb3Al wires for high-field accelerator magnet applications

  K Tsuchiya, S Nimori, T Takeuchi, N Banno, A Kikuchi, Y Iijima, A Terashima, Y Kuroda, T Takao
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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.
• Article: Study of Wires for High-Field Accelerator Magnet Applications

  K. Tsuchiya, T. Takeuchi, N. Banno, A. Kikuchi, Y. Iijima, S. Nimori, H. Takigawa, A. Terashima, A. Yamamoto, Y. Kuroda, T. Takao, K. Tagawa, K. Tanaka, K. Nakagawa
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  ABSTRACT: Rapid heating, quenching and transformation (RHQT)-processed Nb₃Al wires possess better strain tolerance than Nb₃Sn wires. However, RHQT-processed Nb₃Al wires so far developed show lower non-copper critical current density (J_c) than recently developed high-J_c Nb₃Sn wires in the field range of 12-15 T. Therefore, the development of Nb₃Al wires having enhancing J_c in this field range is a major concern for accelerator magnet designers. Among a number of fabrication parameters that might affect J_c properties, we analysed the effect of thickness of Al and Nb foils in the jelly-roll-shaped filaments embedded in the precursor wires. Mechanical and superconducting properties of these wires with various Al-foil thicknesses in the filaments were investigated.
  IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
• Article: Production and Operation of a 15 T Hybrid Magnet System Powered by a Single Power Supply

  T. Takeuchi, N. Banno, Y. Iijima, A. Kikuchi, H. Kitaguchi, M. Yoshikawa, K. Tagawa, K. Nakagawa
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  ABSTRACT: We have recently developed a thin-type Cu clad stabilized Nb₃Al flat-wire which can be more densely wound into a coil. Using this flat-wire we have upgraded an existing 14 T Nb-Ti/Nb₃Sn magnet with a ?? 30 mm clear bore, by replacing the inner coil, to a compact 15 T Nb-Ti/Nb₃Al magnet. The Nb₃Al inner coil was connected in series with the Nb-Ti outer coil and excited by a common power supply to generate 15 T in a ?? 40 mm clear bore, after a training of Nb-Ti coil. The resultant higher field and wider space will be used for critical current measurements of various superconducting wires being developed in NIMS.
  IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
• Article: Microstructural Observation of ITER Strands Under Bending Strain

  N. Banno, T. Takeuchi, N. Koizumi, K. Okuno
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  ABSTRACT: Several efforts are underway to better understand the current degradation phenomenon in ITER Nb₃Sn cable-in-conduit (CIC) conductors, using an electric circuit model of the strand interior. To support these efforts, this paper explores crack formation and filament coupling through microstructural observation of ITER-type Nb₃Sn strands under bending strain. Cracks began to appear at bending strains well below 1%, even in bronze-route Nb₃Sn strands, and typically appeared around 0.3%. In internal-tin Nb₃Sn strands, the strain causing crack formation decreased further, to about 0.25%. Magnetization measurements detected filament coupling, even in bronze-route Nb₃Sn strands. However, the effective filament diameter was so small that its influence on I_c-bending strain characteristics should be limited.
  IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
• Source

  Available from: fnal.gov

  Article: Comparison Between and Strands and Cables for High Field Accelerator Magnets

  R. Yamada, A. Kikuchi, E. Barzi, G. Chlachidze, A. Rusy, T. Takeuchi, M. Tartaglia, D. Turrioni, V. Velev, M. Wake, A.A. Zlobin
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  ABSTRACT: The Nb₃Al small racetrack magnet, SR07, has been successfully built and tested to its short sample limit beyond 10 Tesla without any training. Thus the practical application of Nb₃Al strands for high field accelerator magnets is established. The characteristics of the representative F4 strand and cable, are compared with the typical Nb₃Sn strand and cable. It is represented by the OST high current RRP Nb₃Sn strand with 108/127 configuration. The effects of Rutherford cabling to both type strands are explained and the inherent problem of the Nb₃Sn strand is discussed. Also the test results of two representative small racetrack magnets are compared from the stand point of Ic values, and training. The maximum current density of the Nb₃Al strands is still smaller than that of the Nb₃Sn strands, but if we take into account of the stress-strain characteristics, Nb₃Al strands become somewhat favorable in some applications.
  IEEE Transactions on Appiled Superconductivity 07/2010; · 1.04 Impact Factor
• Article: Characterization of Strands Subjected to an Axial-Strain for a Fusion DEMO Reactor

  T. Hemmi, N. Koizumi, Y. Nunoya, Y. Okui, K. Matsui, Y. Nabara, T. Isono, Y. Takahashi, K. Okuno, N. Banno, A. Kikuchi, Y. Iijima, T. Takeuchi
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  ABSTRACT: A Nb₃Al strand, produced by the ldquorapid-heating, quenching and transformation annealing (RHQT)rdquo process, has been developed in collaboration between JAEA and NIMS aiming at application to the conductor in a fusion DEMO reactor. A detailed description of critical current characteristics of the Nb₃Al RHQT strand may assist in predicting accurate conductor performance. Calculations of the critical current density are adjusted to 5 scaling laws. Advantages of the newly developed strand compared to the Nb₃Sn ITER strand and the Nb₃Al Insert strand include improved strain tolerance and a higher current density at around 16 T. Performance parameters of the Nb₃Al RHQT strand include 450 A/mm² at 15.9 T, 5.7 K and -0.4%. These performance parameters fulfill the requirements of the TF conductor of the fusion DEMO reactor. Therefore, the Nb₃Al RHQT strand represents an improved performance with prospective application in the fusion DEMO reactor. In addition, the Nb₃Al RHQT strand has the potential to enhance further the critical current density.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Article: Quench Tests and FEM Analysis of Rutherford Cables and Small Racetrack Magnets

  R. Yamada, A. Kikuchi, G. Chlachidze, G. Ambrosio, N. Andreev, E. Barzi, R.H. Carcagno, V.V. Kashikin, S. Kotelnikov, M. Lamm, I. Novitski, D. Orris, C. Sylvester, T. Takeuchi, M. Tartaglia, J.C. Tompkins, D. Turrioni, M. Wake, A. Yuan, A.V. Zlobin
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  ABSTRACT: In collaboration between NIMS and Fermilab, we have made copper stabilized Nb₃Al Rutherford cables, using Nb-matrixed and Ta-matrixed strands. First these cables were investigated at high current in low self field using a flux pump. Using these Rutherford cables, we built and tested small racetrack magnets. The magnet made with the Nb-matrixed strand showed the flux jump instability in low field. The small racetrack magnet wound with the Ta-matrixed Nb₃Al Rutherford cable was very stable at 4.5 K operation without any instability, as well as at 2.2 K operation. With the successful operation of the small racetrack magnet up to its short sample data, the feasibility of the Nb₃Al strand and its Rutherford cable for their application to high field magnets is established. The characteristics of Nb₃Al Rutherford cable is compared with that of the Nb₃Sn Rutherford cable and the advantages of Nb₃Al Rutherford cable are discussed.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Article: Development of Ta-Matrix Wire for Next-Generation Accelerator Magnet

  K. Tsuchiya, A. Terashima, A. Yamamoto, C. Mitsuda, T. Takeuchi, N. Banno, S. Nimori, A. Kikuchi, Y. Iijima, T. Fukuda, K. Takenaka, T. Takao, K. Nakagawa, K. Tagawa, K. Tanaka
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  ABSTRACT: We have been developing rapid heating, quenching and transformation (RHQT) processed Nb₃Al wires for next-generation accelerator magnets that require magnetic fields between 12 and 17 T. However, it has recently been found that the conventional Nb-matrix wire shows a rather strong magnetic instability at low fields. Taking this into consideration, we have begun developing Ta-matrix Nb₃Al wires. We have fabricated a precursor wire with a Ta-matrix volume fraction of 0.8, and the mechanical properties of the RHQ-processed wire were examined. The effects of the RHQ condition and the area reduction (AR) after RHQ on the critical current density ( J _c) , and magnetization of the wire have also been examined. This paper describes the properties for the Ta-matrix wire in comparison with those of the Nb-matrix wire.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Source

  Available from: Gen Nishijima

  Article: Quench and Normal Zone Propagation Characteristics of RHQT-Processed Wires Under Cryocooler-Cooling Conditions

  S. Murase, M. Shimoyama, N. Nanato, S.B. Kim, G. Nishijima, K. Watanabe, A. Kikuchi, N. Banno, T. Takeuchi
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  ABSTRACT: The minimum quench energy ( MQE ) and normal zone propagation velocity ( NZPV ) of three kinds of Nb₃Al superconductors fabricated by the rapid heating, quenching and transformation (RHQT) process were measured under various conditions of applied magnetic field (10-14 T), temperature (7-11 K), and transport current (80-95% of the critical current), while cooled by a cryocooler for developing the over 20-T class cryogen-free magnet. As a result, MQE values were related to the critical current density ( J _c); high MQE was obtained for low J _c. It is assumed that J _c has a stronger influence on the MQE than specific heat, thermal conductivity, resistivity, and other parameters of the composite superconductor including the matrix and the stabilizer. NZPV was mainly proportional to the transport current density varying with applied field and temperature. The second contribution to NZPV is assumed to be heat capacity depending on the wire configuration.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Article: Design and Loading Test Results of 21 T@4.2 K Magnet Using RHQT Insert Coils

  T. Takeuchi, H. Kitaguchi, N. Banno, Y. Iijima, A. Kikuchi, M. Yoshikawa
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  ABSTRACT: In this experiment, we designed, constructed and tested a 21 T superconducting magnet to be operated at 4.2 K, consisting of a Nb₃Al inner coil with an exclusive power supply, and a series of Nb₃Al middle, Nb₃Sn outer-1 and Nb-Ti outer-2 coils with a common power supply. The flux jumps of the Nb₃Al middle coil occurred in low magnetic fields and caused frequent shutdowns of an overvoltage-sensitive common power supply; however, we discovered this could be avoided by reducing the current ramp rate. The outer-middle coil unexpectedly quenched at 17.7 T, which was less than the expected 19.3 T. Simultaneous excitation of the inner coil was scarcely effective in increasing the quench current of the outer-middle coil, indicating that the Ic degraded location is relatively far from the inner coil. However, energization of the inner coil to a quench, in a backup field of 17.6 T by the outer-middle coil generated a central field of 20 T in a 25.4 mm clear bore at 4.2 K.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Article: Superconducting Properties of Wire Fabricated by Diffusion Reaction Between Ag-Sn-Mg Alloy and Nb

  M. Iwatani, K. Inoue, T. Takeuchi, T. Kiyoshi
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  ABSTRACT: Mg addition improves T _c, B _irr, and I _c of the Nb₃Sn formed by diffusion reaction between Nb and Ag-Sn alloy, when the diffusion reaction is performed below 650 ^degC. The obtained superconducting properties are similar to those of the bronze-processed Nb₃Sn. The formation temperature of Nb₃Sn is reduced by the Mg addition. By using OM, SEM, and field emission type EPMA, we could not measure the thickness of Nb₃Sn layers, which may be thinner than 0.5 mum. It is not clear that the Mg addition increases the formation rate of Nb₃Sn. However, the Nb₃Sn layers should have very high J _c. The attainable overall J _c of the Nb₃Sn wire are as high as those of the bronze-processed Nb₃Sn wire without Ti and Ta additions, although the optimization of the cross-sectional configuration of Nb and Ag-Sn-Mg in the wire has not yet performed. Therefore the potential of the Nb₃Sn conductor made by the new process seems to be very attractive for the practical applications.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Article: Development of Fine Multifilamentary Conductors

  N. Banno, T. Takeuchi, K. Tanaka, K. Nakagawa, S. Nimori, Y. Iijima, A. Kikuchi
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  ABSTRACT: A new configuration of Nb₃Al conductor with a fine multifilamentary structure is presented. The wire is fabricated by a simple re-stacking (RS) method, in which rapid-quenched ductile BCC Nb-Al phase wires are re-stacked into a stabilizing Cu tube and co-drawn into a final form. Such a simple stabilization method will be effective to cut the Nb₃Al fabrication cost. The developed RS Nb₃Al conductor has a non-Cu J _c of almost about 1000 A/mm² at 15 T, 4.2 K. The effective filament diameter is 14 mum and the hysteresis loss (+/- 3 T) is 370 mJ/cm³, which is small enough with respect to the ITER target specification.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Source

  Available from: fnal.gov

  Article: Characteristics of Cu Stabilized Strands With Low Cu Ratio

  A. Kikuchi, R. Yamada, E. Barzi, M. Kobayashi, M. Lamm, K. Nakagawa, K.-i. Sasaki, T. Takeuchi, D. Turrioni, A.V. Zlobin
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  ABSTRACT: Characteristics of recently developed F4-Nb₃Al strand with low Cu ratio are described. The overall J _c of the Nb₃Al strand could be easily increased by decreasing of the Cu ratio. Although the quench of a pulse-like voltage generation is usually observed in superconducting unstable conductor, the F4 strand with a low Cu ratio of 0.61 exhibited an ordinary critical transition of gradual voltage generation. The F4 strand does not have magnetic instabilities at 4.2 K because of the tantalum interfilament matrix. The overall J _c of the F4 strand achieved was 80-85% of the RRP strand. In the large mechanical stress above 100 MPa, the overall J _c of the F4 strand might be comparable to that of high J _c RRP-Nb₃Sn strands. The Rutherford cable with a high packing factor of 86.5% has been fabricated using F4 strands. The small racetrack magnet, SR07, was also fabricated by a 14 m F4 cable. The quench current, I _q, of SR07 were obtained 22.4 kA at 4.5 K and 25.2 kA at 2.2 K. The tantalum matrix Nb₃Al strands are promising for the application of super-cooled high-field magnets as well as 4.2 K operation magnets.
  IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
• Article: Minimization of the hysteresis loss and low-field instability in technical Nb3Al conductors

  N Banno, T Takeuchi, S Nimori, K Tanaka, K Nakagawa, K Tsuchiya
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  ABSTRACT: This paper focuses on the magnetization characteristics of technical Nb3Al conductors, in particular the minimization of their hysteresis loss and low-field instability. Unlike the case of Nb3Sn wire fabrication, the Nb3Al wire is fabricated by a phase transformation process, in which it is believed that the Jc properties of the transformed Nb3Al phase do not depend on the filament size or shape, but rather are principally controlled by the rapid heating and quenching or transformation conditions. However, the rapid heating and quenching process forces us to use high-melting-point metals like niobium as the matrix. The use of Nb strongly affects the magnetization because of its superconductivity in low fields. In this paper, the magnetization properties of several kinds of technical Nb3Al conductors, including Ta matrix wires, were studied. The use of Ta was effective in suppressing low-field instability. In addition, we propose a new process to further minimize the filament diameter by a re-stacking (RS) method, whereby the rapidly quenched strands are re-stacked into a stabilizing material tube and co-drawn. This process leads to a very fine multifilamentary structure with a filament diameter of less than 15 µm, thereby substantially reducing the magnetization, as compared with high-performance Nb3Sn wires, e.g. RRP Nb3Sn wire. The ± 3 T hysteresis loss of the RS Nb3Al conductor was 370 mJ cm−3 and the non-Cu Jc (12 T, 4.2 K) of the conductor was 1350 A mm−2. These values meet the ITER strand specification.
  Superconductor Science and Technology 09/2008; 21(11):115020. · 2.66 Impact Factor
• Article: Cu Stabilized Strands for the High Field Accelerator Magnet

  A. Kikuchi, R. Yamada, E. Barzi, M. Lamm, T. Takeuchi, D. Turrioni, A.V. Zlobin
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  ABSTRACT: Characteristics of developed Nb₃Al strand though the RHQT (rapid heating/quenching and transformation) process are described. One kilometer-long copper stabilized Nb₃Al round strands were economically fabricated with ion-plating and electroplating. The copper electroplating was successfully done with the high velocity of 5 m/h. A strong bonding between the copper and the precursor was achieved, and the mechanical rolling test did not show the separation of the copper stabilizer from the precursor. The rolled Nb₃Al strands showed no degradation both in critical current density and RRR value. Magnetic instability at 4.2 K at low fields was apparently improved on the F3 strand, relative to the previously F1 stand because a tantalum was used for the interfilament matrix of precursor. The large magnetic flux jumps, which were observed with the Fl strand, were suppressed at 4.2 K, although appeared again below 3.0 K. The twisted strands are shown to be effective to reduce the time-dependent eddy current coupling. It was obtained 48 mum of D_eff on F3 strand with twist pitch of 45 mm. In addition, the transverse pressure test for the Fl Nb₃Al strand was performed at 4.2 K and 12 T. The critical current did not degrade with the transverse pressure up to 210 MPa.
  IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor
• Article: Development of RHQT-Processed Wire for High-Field Accelerator Magnet Applications

  K. Tsuchiya, C. Mitsuda, A. Terashima, A. Yamamoto, T. Takeuchi, N. Banno, S. Nimori, A. Kikuchi, Y. Iijima, K. Okamoto, T. Fukuda, K. Takenaka, T. Takao, K. Tagawa
  [show abstract] [hide abstract]
  ABSTRACT: In the development of RHQT-processed Nb₃Al wires for high-field accelerator magnet applications, one of the major objectives is to increase the non-copper critical current density in the field range of 12-15 T. To pursue this goal, a low-matrix- ratio wire was fabricated, and the effects of the RHQ conditions and the area reduction after the RHQ treatment on the properties of the wire were investigated. This paper describes the details and results of this study.
  IEEE Transactions on Appiled Superconductivity 07/2008; · 1.04 Impact Factor