In the last 30 days

• Open/close Superconducting wind turbine generators

  A B Abrahamsen et al 2010 Supercond. Sci. Technol. 23 034019 Tag this article

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  We have examined the potential of 10 MW superconducting direct drive generators to enter the European offshore wind power market and estimated that the production of about 1200 superconducting turbines until 2030 would correspond to 10% of the EU offshore market. The expected properties of future offshore turbines of 8 and 10 MW have been determined from an up-scaling of an existing 5 MW turbine and the necessary properties of the superconducting drive train are discussed. We have found that the absence of the gear box is the main benefit and the reduced weight and size is secondary. However, the main challenge of the superconducting direct drive technology is to prove that the reliability is superior to the alternative drive trains based on gearboxes or permanent magnets. A strategy of successive testing of superconducting direct drive trains in real wind turbines of 10 kW, 100 kW, 1 MW and 10 MW is suggested to secure the accumulation of reliability experience. Finally, the quantities of high temperature superconducting tape needed for a 10 kW and an extreme high field 10 MW generator are found to be 7.5 km and 1500 km, respectively. A more realistic estimate is 200–300 km of tape per 10 MW generator and it is concluded that the present production capacity of coated conductors must be increased by a factor of 36 by 2020, resulting in a ten times lower price of the tape in order to reach a realistic price level for the superconducting drive train.

• Open/close Intrinsic phase separation in superconducting K_0.8Fe_1.6Se₂ (T_c = 31.8 K) single crystals

  Alessandro Ricci et al 2011 Supercond. Sci. Technol. 24 082002 Tag this article

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  Temperature dependent single-crystal x-ray diffraction (XRD) in transmission mode probing the bulk of the newly discovered K _0.8Fe _1.6Se ₂ superconductor ( T _c = 31.8 K) using synchrotron radiation is reported. A clear evidence of intrinsic phase separation at 520 K between two competing phases, (i) a first majority magnetic phase with a ThCr ₂Si ₂-type tetragonal lattice modulated by the iron vacancy ordering and (ii) a minority non-magnetic phase having an in-plane compressed lattice volume and a weak superstructure, is reported. The XRD peaks due to the Fe vacancy ordering in the majority phase disappear on increasing the temperature to 580 K, well above phase separation temperature, confirming the order–disorder phase transition. The intrinsic phase separation at 520 K between a competing first magnetic phase and a second non-magnetic phase in the normal phase both having lattice superstructures (that imply different Fermi surface topology reconstructions and charge densities) is assigned to a lattice-electronic instability of the K _0.8Fe _1.6Se ₂ system typical of a system tuned at a Lifshitz critical point of an electronic topological transition that gives a multigap superconductor tuned to a shape resonance.

• Open/close An overview on iron based superconductors

  P M Aswathy et al 2010 Supercond. Sci. Technol. 23 073001 Tag this article

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  The discovery of superconductivity at relatively higher temperatures in a non-cuprate system, LnFeAsO _{1 − x}F _x (Ln = lanthanides) has created tremendous activity among the reseachers in this field. This review is an overview on the present status and the future scope for iron pnictides. The various structural categories of iron based superconductors, the structural aspects, different preparation techniques of the material and the necessity for its optimization are discussed. The highlighting features of iron pnictide, i.e. the very high upper critical field, moderate magneto-transport and thermal properties, are also included. The article gives a summary of the prevailing arguments of researchers to relate the material to cuprates and also the comparative features of classical and MgB ₂ superconductors. The existing challenges, such as optimizing synthesis methods for technological applications and clarifying the ambiguity in the superconducting mechanism and the flexibility of the material for any site substitution, will keep iron based superconductors on the frontiers of research for a long time, in parallel to HTS.

• Open/close High-temperature superconductor fault current limiters: concepts, applications, and development status

  Mathias Noe and Michael Steurer 2007 Supercond. Sci. Technol. 20 R15 Tag this article

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  The application of superconducting fault current limiters (SCFCLs) in power systems is very attractive because SCFCLs offer superior technical performance in comparison to conventional devices to limit fault currents. Negligible impedance at normal conditions, fast and effective current limitation within the first current rise and repetitive operation with fast and automatic recovery are the main attributes for SCFCLs.

  In recent years there has been a significant progress in the research and development (R&D) of SCFCLs. This paper gives an extended review of different SCFCL concepts, SCFCL applications and the R&D status. Within the first part of this paper the most important SCFCLS and, to a limited extent, non-superconducting fault current limiter (FCL) concepts are explained and compared. The second part reviews interesting SCFCL applications at the distribution and transmission voltage level and the third part shows in detail the R&D status.

  It can be summarized that SCFCLs are, at present, not commercially available but several successful field tests demonstrated the technical feasibility of SCFCLs. First distribution level applications are expected soon. Considerable economical and technical benefits can be achieved by applying SCFCLs at the distribution and transmission voltage level.

• Open/close Microstructural and superconducting properties in single-domain Gd–Ba–Cu–O bulk superconductors with in situ formed Fe₃O₄ ferrimagnetic particles

  Kun Xu et al 2011 Supercond. Sci. Technol. 24 085001 Tag this article

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  Introducing secondary-phase inclusions into the superconducting matrix is regarded as an effective way to enhance the flux pinning performance of high temperature superconductors. The effect of Fe–B alloy additives on the microstructure and superconducting properties of top-seeded melt growth processed GdBa ₂Cu ₃O _{7 − δ} /Ag bulk superconductors has been investigated systematically. GdBa ₂Cu ₃O _{7 − δ} /Ag bulks 17 mm in diameter were melt-textured for various amounts of Fe–B additives in the range of 0–1.4 mol%. By means of scanning and transmission electron microscopy observations, the Fe–B alloy additives were found to decompose into ferrimagnetic Fe ₃O ₄, embedded inside or in the vicinity of silver particles. These ferrimagnetic particles may assist in reducing the Lorentz force exerted on the vortices and enhance the flux trapping capability and critical current density of Gd–Ba–Cu–O bulks. It was also found that the refinement of Gd ₂BaCuO ₅ and its homogeneous distribution was improved together with increase of the number of Gd ₂BaCuO ₅ particles when we increase the addition of Fe–B alloy particles. The amount added introduces a systematic change in the particle distribution dependent on both size and the numbers. The observed enhancement of the trapped flux may inherently include the magnetic interactions between the ferrimagnetic Fe ₃O ₄ with the surrounding compounds, which has a critical effect on the nucleation process of Gd ₂BaCuO ₅ inclusions.

• Open/close Physical property and electronic structure characterization of bulk superconducting Bi₃Ni

  Jagdish Kumar et al 2011 Supercond. Sci. Technol. 24 085002 Tag this article

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  We report the experimental and theoretical study of the magnetic nature of the Bi ₃Ni system. The structure is found to be orthorhombic ( Pnma) with lattice parameters a = 8.879 Å, b = 4.0998 Å and c = 4.099 Å. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5 N purity stoichiometric ingredients of Ni and Bi. The superconducting transition temperature is found to be 4.1 K as confirmed from magnetization and specific heat measurements. The lower critical field ( H _c1) and irreversibility field ( H _irr) are around 150 and 3000 Oe respectively at 2 K. Upper critical field ( H _c2), as determined from in-field (up to 4 T) ac susceptibility, is found to be around 2 T at 2 K. The normal state specific heat is fitted using the Sommerfeld–Debye equation C( T) = γ T + β T ³ + δ T ⁵ and the parameters obtained are γ = 11.08 mJ mol ^{− 1} K ^{− 2}, β = 3.73 mJ mol ^{− 1} K ^{− 4} and δ = 0.0140 mJ mol ^{− 1} K ^{− 6}. The calculated electronic density of states (DOS) at the Fermi level N( E _F) and Debye temperature Θ _D are 4.697 states/eV/f.u. and 127.7 K respectively. We also estimated the value of the electron–phonon coupling constant (λ) to be 1.23, which when substituted in the MacMillan equation gives T _c = 4.5 K. Density functional theory (DFT) based calculations for experimentally determined lattice parameters show that Ni in this compound is non-magnetic and ferromagnetic interactions seem to play no role. The Stoner condition IN( E _F) = 0.136 per Ni atom also indicates that the system cannot have any ferromagnetism. The fixed spin moment (FSM) calculations, by fixing total magnetic moment on the unit cell, also suggested that this system does not exhibit any signatures of ferromagnetism.

• Open/close Alcoholic beverages induce superconductivity in FeTe_{1 − x}S_x

  K Deguchi et al 2011 Supercond. Sci. Technol. 24 055008 Tag this article

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  We found that hot alcoholic beverages were effective in inducing superconductivity in FeTe _0.8S _0.2. Heating the FeTe _0.8S _0.2 compound in various alcoholic beverages enhances the superconducting properties compared to a pure water–ethanol mixture as a control. Heating with red wine for 24 h leads to the largest shielding volume fraction of 62.4% and the highest zero resistivity temperature of 7.8 K. Some components present in alcoholic beverages, other than water and ethanol, have the ability to induce superconductivity in the FeTe _0.8S _0.2 compound.

• Open/close An overview of Boeing flywheel energy storage systems with high-temperature superconducting bearings

  M Strasik et al 2010 Supercond. Sci. Technol. 23 034021 Tag this article

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  An overview summary of recent Boeing work on high-temperature superconducting (HTS) bearings is presented. A design is presented for a small flywheel energy storage system that is deployable in a field installation. The flywheel is suspended by a HTS bearing whose stator is conduction cooled by connection to a cryocooler. At full speed, the flywheel has 5 kW h of kinetic energy, and it can deliver 3 kW of three-phase 208 V power to an electrical load. The entire system, which includes a containment structure, is compatible with transportation by forklift or crane. Laboratory measurements of the bearing loss are combined with the parasitic loads to estimate the efficiency of the system. Improvements in structural composites are expected to enable the operation of flywheels with very high rim velocities. Small versions of such flywheels will be capable of very high rotational rates and will likely require the low loss inherent in HTS bearings to achieve these speeds. We present results of experiments with small-diameter rotors that use HTS bearings for levitation and rotate in vacuum at kHz rates. Bearing losses are presented as a function of rotor speed.

• Open/close Compact GdBa₂Cu₃O_7–δ coated conductor cables for electric power transmission and magnet applications

  D C van der Laan et al 2011 Supercond. Sci. Technol. 24 042001 Tag this article

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  Bundling high-temperature superconductors together to form high-current cables is required in, for instance, power transmission and low-inductance magnet applications. Cabling techniques that have been applied so far have not resulted in compact, mechanically robust, high-current cables that remain flexible. Here, we demonstrate that the cabling technique that we have introduced only recently enables the construction of cables from high-temperature superconducting coated conductors that meet these requirements. We present details of a cable, wound from GdBa ₂Cu ₃O _7–δ coated conductors, that has an outer diameter of 7.5 mm and a critical current of about 2800 A at 76 K and self-field. The compact size and flexibility make the cable suitable for Navy and Air Force power transmission, and would allow superconducting power transmission lines that have been installed in the electric power grid to be reduced in diameter. The potential of increasing the engineering current density of the cable, while maintaining flexibility, makes them also suitable for high-field magnet applications.

• Open/close Pure bending strains of Nb₃Sn wires

  Makoto Takayasu et al 2011 Supercond. Sci. Technol. 24 045012 Tag this article

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  This paper presents in detail recent pure bending strain investigations of ITER Nb ₃Sn wires including a pure bending device development, bending effects on the critical currents and their model analyses. The pure bending test device allows applying a uniform bending over a large range of bending strain on a strand sample under a large electromagnetic Lorentz force. Pure bending characteristics of five different Nb ₃Sn wires including three internal tin and two bronze wires were tested and evaluated with a newly developed integrated model that accounts for neutral axis shift, current transfer length, mechanical filament breakage and uniaxial strain release due to the applied bending load.