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Eltsev Y.,RAS Lebedev Physical Institute | Lee S.,Tokyo Superconductivity Research Laboratory | Nakao K.,Tokyo Superconductivity Research Laboratory | Tajima S.,Tokyo Superconductivity Research Laboratory
Superconductor Science and Technology | Year: 2010

We have studied electrical transport properties of a high quality Bi 2Sr2Ca2Cu3O10 + x crystal below a superconducting critical temperature, Tc. In magnetic fields B parallel to the c axis just above a voltage response onset resistance versus temperature data are well fitted to the vortex-glass model. Obtained from the vortex-glass analysis, a melting transition boundary for Bi-2223 crystal is shifted towards lower temperatures compared to previously reported data for a (Bi, Pb)-2223 single crystal. The critical current density, Jc, of Bi-2223 crystals is close to Jc values presented elsewhere for Bi-2223 tapes, suggesting a principal role of weak intrinsic pinning properties of Bi-2223 as a main limiting factor of Jc of Bi-2223 conductors. © 2010 IOP Publishing Ltd.

Maruyama O.,Tokyo Superconductivity Research Laboratory | Ohkuma T.,Tokyo Superconductivity Research Laboratory | Izumi T.,Tokyo Superconductivity Research Laboratory
Physics Procedia | Year: 2013

Japanese nati - FY2008. In this project, high temperature superconducting (HTS) cable using REBCO tapes has been developing. These HTS cables are expected as a compact size with large capacity and low loss power transmission. In the future, it is supposed that these cables will be installed in power grid for replacing existing power cables. Under the operating HTS cable in the power grid, it is necessary that the REBCO tapes in the long distance cable are kept cooling at low temperature stably and efficiently by liquid nitrogen (LN 2). In this paper, the flow characteristic, such as pressure drop of LN2 flowing in the long distance HTS cable, and the heat transfer characteristic against heat generation, such as AC loss, and heat leak from cryostat-pipes were analytically estimated with varying the volumetric flow and the diameter of outer pipe wall which are parameters easy to control in cable system design. As a result, it was confirmed that the volumetric flow increasing is affective to extending the maximum distance which can be transmitted but it required increasing discharge pressure too. This increasing discharge pressure can be restricted without affecting the longitudinal distribution of the HTS temperature by expanding of the diameter of outer pipe wall. © 2013 The Authors.

Takeuchi K.,Kyoto University | Amemiya N.,Kyoto University | Nakamura T.,Kyoto University | Maruyama O.,Tokyo Superconductivity Research Laboratory | Ohkuma T.,Tokyo Superconductivity Research Laboratory
Superconductor Science and Technology | Year: 2011

Since the superconductor layers of YBCO-coated conductors are very thin, the ac loss of coated conductors is dominated by the magnetic flux density normal to the conductor face. In cables, most of the normal magnetic flux component is generated near gaps between coated conductors. Although the effects of gaps are significant, there are few reports on the electromagnetic field analysis of cables with spiral structures carried out while taking the gap effect into consideration. In a finitely long cable with a spiral structure, the electromagnetic field is naturally periodic along the cable axis. In a two-layer cable, the simplest period along the cable axis is the least common multiple of the spiral pitches in the inner and outer layers. However, we verified that there is a shorter period, and the same electromagnetic field distribution appears in all conductors of the same layer. Using these periodicities, we developed a three-dimensional model for the analysis of two-layer cables with a spiral structure. Current distributions of cables were analyzed using this model, and ac losses were calculated. In addition, these results were compared with ac losses calculated by two-dimensional analysis performed on the cross section of a cable. It was verified that the ac loss in a cable is correctly calculated by the 2D model when the spiral pitch is long enough. However, in the case of a tightly twisted cable, the ac losses calculated by the 2D model include some errors caused by an approximation in which the spiral structure is ignored. © 2011 IOP Publishing Ltd.

Haberkorn N.,Los Alamos National Laboratory | Maiorov B.,Los Alamos National Laboratory | Usov I.O.,Los Alamos National Laboratory | Weigand M.,Los Alamos National Laboratory | And 6 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

In this work we analyze the influence of random point defects introduced by 3 MeV proton irradiation on the critical current density (J c) and vortex dynamics of a Ba(Fe 0.925Co 0.075) 2As 2 single crystal. The results show that at low temperatures (T) the irradiation produces an enhancement of J c of up to 2.6 times. However the J c (T) retention at different magnetic fields (H) in the elastic regime, estimated by the n exponent in J c vs (1 -(T /T c )2 )n, is poorer after the irradiations due to the thermal softening of the pinning by the random point defects. We found that the elastic-to-plastic crossover and melting lines are only affected by the reduction of the superconducting critical temperature (T c); they are exactly the same after rescaling the phase diagram by T/T c. The pinning mechanisms in the single crystals can be associated with a mixed pinning landscape that produces a modulation in S(H, T) as a consequence of a fishtail or second peak in the magnetization. © 2012 American Physical Society.

Mawatari Y.,Japan National Institute of Advanced Industrial Science and Technology | Malozemoff A.P.,American Superconductor Corporation | Izumi T.,Tokyo Superconductivity Research Laboratory | Tanabe K.,Tokyo Superconductivity Research Laboratory | And 2 more authors.
Superconductor Science and Technology | Year: 2010

Hysteretic ac losses in monolayer power transmission cables with superconducting tapes are theoretically investigated. The ac losses depend on the tape shape and the cable configuration. The ac losses in two types of ideal cables are compared: the ac loss Qrnd in a round cable with curved superconducting tapes conforming to a cylindrical former, and the ac loss Q agl in an angular cable with flat superconducting tapes. The Q agl is larger than Qrnd because of the polygonal cross section of the angular cable, and the tape-width dependence of Qagl is very different from that of Qrnd. © 2010 IOP Publishing Ltd.

Miura M.,Tokyo Superconductivity Research Laboratory | Miura M.,Japan Society for the Promotion of Science | Yoshizumi M.,Tokyo Superconductivity Research Laboratory | Izumi T.,Tokyo Superconductivity Research Laboratory | Shiohara Y.,Tokyo Superconductivity Research Laboratory
Superconductor Science and Technology | Year: 2010

Grains of BaZrO3 (BZO) in REBa2Cu3O y (REBCO) films exhibit microstructural differences, depending on whether they were deposited by pulsed-laser deposition (PLD) or metal-organic deposition (MOD). In order to understand the origins of these differences, we examined the formation mechanism of BZO nanoparticles in the MOD process with detailed observations of the quenched films by transmission electron microscopy. The BZO nanoparticle was found to form in the precursor during the temperature ramp prior to the formation of the Y1-xSmxBa 2Cu3Oy (YSmBCO) crystals. The YSmBCO grew layer by layer while entrapping the BZO particles, which resulted in random dispersion of the BZO particles in the YSmBCO layer. Consequently, uniformly dispersed BZO nanoparticles were formed in the YSmBCO matrix derived from the TFA-MOD process. These findings indicate that a key factor in achieving fine dispersion of BZO nanoparticles in the superconducting matrix is strongly related to nucleation of the BZO phase crystals in the precursor before growth of the YSmBCO layer, which is unique to the MOD process. In subsequent testing, YSmBCO-coated conductors with uniformly dispersed and densely concentrated BZO nanoparticles showed striking isotropic magnetic-field angular dependence of critical currents. © 2010 IOP Publishing Ltd.

Amemiya N.,Kyoto University | Nakahata M.,Yokohama National University | Fujiwara N.,Tokyo Superconductivity Research Laboratory | Shiohara Y.,Tokyo Superconductivity Research Laboratory
Superconductor Science and Technology | Year: 2010

Electromagnetic field analyses were made in cross-sections of two-layer superconducting power transmission cables consisting of coated conductors to calculate their ac losses, neglecting the spiral arrangement of the coated conductor and assuming each coated conductor was parallel to the cable axis. A substrate of each coated conductor was placed inside when assembling the coated conductors into a cable. Based on the electromagnetic field analyses, ac losses in the superconductor layer in the coated conductor as well as those in the magnetic substrate were calculated. The magnetism of the substrate increases ac losses in the outer-layer coated conductors and in the inner-layer coated conductors in different ways. In outer-layer coated conductors, the hysteretic loss in the magnetic substrate itself dominates their ac losses, because their magnetic substrates are directly exposed to the magnetic field produced by the inner-layer current. In inner-layer coated conductors, ac loss in the superconductor layer increases, because the magnetic substrate of the outer-layer coated conductor attracts magnetic flux to increase the magnetic field component normal to the superconductor layer of the inner-layer coated conductor. The influence of the space between the two layers as well as the width of the coated conductor on the ac loss characteristics is also discussed. © 2010 IOP Publishing Ltd.

Machi T.,Tokyo Superconductivity Research Laboratory | Nakao K.,Tokyo Superconductivity Research Laboratory | Kato T.,Japan Fine Ceramics Center | Hirayama T.,Japan Fine Ceramics Center | Tanabe K.,Tokyo Superconductivity Research Laboratory
Superconductor Science and Technology | Year: 2013

We have developed a reliable fabrication process based on a laser scribing method for multi-filamentary coated conductors with a low alternating current loss. This process consists of shallow laser irradiation and two-step chemical etching. The shallow laser irradiation, which penetrates into only a masking polymer tape and a silver stabilizing layer, suppresses generation of dross that is formed due to melting and hardening of a metal substrate. The two-step chemical etching individually for the stabilizing and the superconducting layers prevents over-etching of the superconducting layer and thus suppresses degradation of the critical current (Ic). By using the developed laser scribing process, we realized an improvement of processing speed and a reduction of Ic degradation at the same time. Subsequently, we developed reel-to-reel equipment to apply this process to coated conductors several hundred meters long. We succeeded in fabricating 280 m and 70 m long coated conductors with 5 mm width divided into three and five filaments, respectively. It was confirmed that they had one-third and one-fifth hysteresis loss, respectively, in comparison with that before processing, and high inter-filament resistance, over 0.1 MΩ cm. The typical degradation rates of Ic in the developed laser scribing process were less than 20%. © 2013 IOP Publishing Ltd.

Izumi T.,Tokyo Superconductivity Research Laboratory | Shiohara Y.,Tokyo Superconductivity Research Laboratory
Physica C: Superconductivity and its Applications | Year: 2010

On the research and development of coated conductors in Japan, the I c characteristics and the length have been remarkably improved in the national project. Five hundred meter-long tapes with higher Ic values than 300 A/cm-width were realized by the pulsed laser deposition (PLD) and the metal organic deposition using trifluoroacetates (TFA-MOD) processings for the superconducting layer on the IBAD-GZO buffered substrates. In order to realize the low cost by the increasing the production rate of the ion beam assisted deposition (IBAD) layer, the process of IBAD-MgO was developed and a 1000 m-long IBAD buffer tape was fabricated at an extremely high production rate of 1 km/h. On the other hand, the artificial pinning center has been introduced in both PLD and MOD processing. The BaZrO3 nano-rods were aligned along the caxis of GdBCO superconducting films by the PLD process. The J c value in the magnetic field parallel to the c-axis was remarkably improved. Additionally, the BaZrO3 nano-particles were uniformly dispersed in YGdBCO films by the TFA-MOD process and the Jc-B-θ property was confirmed to be isotropic. Based on the above-mentioned achievements, the new national project, whose main objective is the development of some electric power applications using a coated conductor, started in 2008. In this project, the improvement of the coated conductor includes the five sub-themes: (1) degradation of tapes, (2) high Ic under magnetic field, (3) low AC loss, (4) high mechanical strength and high Je and (5) low cost and high yield. © 2010 Elsevier B.V. All rights reserved.

Tanabe K.,Tokyo Superconductivity Research Laboratory | Hosono H.,Tokyo Superconductivity Research Laboratory | Hosono H.,Tokyo Institute of Technology
Japanese Journal of Applied Physics | Year: 2012

The recent discovery of iron-based superconductors has evoked enthusiasm for extensive research on these materials because they form the second high-temperature superconductor family after the copper oxide superconductors and impart an expectation for materials with a higher transition temperature (T c). It has also been clarified that they have peculiar physical properties including an unconventional pairing mechanism and superconducting properties preferable for application such as a high upper critical field and small anisotropy. This paper reviews the research on thin films, Josephson junctions, and superconducting wires and tapes made from iron-based superconductors, which has been performed toward the realization of future applications. Though there are many technical hurdles toward the practical application of these materials, some promising features such as a high critical current density in thin films under high magnetic fields and advantageous grain boundary properties over copper oxides have been clarified. © 2012 The Japan Society of Applied Physics.

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