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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. Source

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. Source

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. Source

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. Source

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. Source

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