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SMES technology based on MgB 2 superconductor and cryogenic-free cooling can offer a viable solution to power-intensive storage in the short term. One of the main obstacles to the development of dry-cooled SMES systems is the heat load removal due to the AC loss of the superconductor during fast charging and discharging cycles at high power. Accurate knowledge of the amount and distribution of AC loss in the coil is of paramount importance for the sizing and the design of the cooling system and for assessing the possible operational limits of the technology. In this manuscript, the AC loss of a 500 kJ/200 kW multifilamentary MgB 2 SMES during charge–discharge cycling at full power is numerically investigated. The methodology and assumptions of the calculation are briefly resumed, and numerical results are reported and discussed in detail. In particular, the time profile and the distribution of the dissipated power all over the coil are reported. An average dissipation of 85.5 mW/m is found all over the coil during one charge–discharge cycle at full power, with a peak of 150.1 mW/m in the turns lying at the ends of the coil. [ABSTRACT FROM AUTHOR]

Mg[B.sub.2] tapes and wires are prepared by using the ex-situ Powder-In-Tube (PIT) method and the effects of using different metallic materials for the sheaths in new round or square shaped multifilamentary wires are studied. The TEM analysis has highlighted the role played by the amorphous layer at the grain boundaries.

Various studies have been conducted to devise methods for the improvement of the magnetic behavior of the magnesium diboride tapes, which are produced through the ex-situ Powder-In-Tube (PIT) method. The insertion of SiC nanoparticles in the precursors is found to enhance the in-field properties of the tapes.

A three-year research project, called DRYSMES 4GRID, was recently funded by the Italian Minister of Economic Development, Italy. The project, which involves five Italian partners (companies, universities, and research institutes), is aimed to demonstrate the feasibility of cost-competitive SMES based on magnesium diboride (MgB2 ) with a cryogen-free cooling bymeans of the manufacturing and the testing of a demonstrator with an objective rating of 500 kJ/200 kW. This rating is deemed suitable for disclosing the critical technological aspects of all components in view of practical applications. A further goal of the project is the assessment of the technical and economic benefits that the SMES can bring to real-world electric grids. The general outline and technical objectives of the project are presented in this paper. Preliminary design assumptions and results concerning the MgB2 coil and the power condition system are also discussed. [ABSTRACT FROM AUTHOR]

The critical currents of several configurations of MgB2 conductors from Columbus Superconductors SpA were characterized under high magnetic fields. The measurements were performed at LNCMI Grenoble at a temperature of 4.2 K and under a magnetic field ranging from 3 up to 8 T. The characterization of the different configurations takes into account different parameters, such as the filling factor, number of filaments, shape, and type of matrix. Moreover, in order to define the minimum bending radius, the different samples were prebent at room temperature on different diameters (from 50 to 400 mm) and then straightened again before being tested. This work investigates the critical current density Jc, engineering current density Je, and the influence of bending strain over the critical current. The different samples are compared according to their critical current densities, engineering densities, and bending strain tolerances. [ABSTRACT FROM AUTHOR]

The SUPRAPOWER, an EU FP7 funded research project, is developing an innovative 10 MW class superconducting generator to provide an important breakthrough in the offshore wind industry. The 10 MW generators adopts modular concept to the superconducting coil and associated cryogenic systems. And the modular superconducting coil and cryostat of this novel generator will be validated through a scale-down rotating magnetic validator (RMV). The cryogenic cooling system for the RMV consists of two modular cryostats: a distributing cryostat and the corresponding rotating cryocooler system with a self-developed rotary joint. In order to achieve the SC coils' working temperature of 20 K, a two-stage G-M cryocooler will be applied and linked to the two modular cryostats by way of a conductive copper connection. The distributing cryostat was developed to envelop the cold head of the cryocooler, thermal link, and three binary current leads to electrically feed the coils. A rotary joint with Ferrofluid sealing was developed to transfer the helium gas between the rotating cold head and stationary oil-lubricated compressor. In this paper, the design, manufacture, and assembly of this cryogenic system for RMV will be presented in detail. [ABSTRACT FROM AUTHOR]

In this paper we report a detailed µ+SR and 19F NMR study of the La0.7Y0.3FeAsO1− xF x class of materials. Here, the diamagnetic La1− yY y substitution increases chemical pressure and, accordingly, sizeably enhances the optimal superconducting transition temperature. We investigate the magnetic-superconducting phase transition by keeping the Y content constant ( y = 0.3) and by varying the F content in the range $0.025\leq x\leq 0.15$. Our results show how magnetism and superconductivity coexist for x = 0.065. Such coexistence is due to segregation of the two phases in macroscopic regions, resembling what was observed in LaFeAsO1− xF x materials under applied hydrostatic pressure. This scenario is qualitatively different from the nanoscopic coexistence of the two order parameters observed when La is fully substituted by magnetic rare-earth ions like Sm or Ce. [ABSTRACT FROM AUTHOR]

We investigate the effect of external pressure on magnetic order in undoped LnFeAsO (Ln = La, Ce, Pr, Sm) by using muon spin relaxation measurements and ab initio calculations. Both the magnetic transition temperature Tm and the Fe magnetic moment decrease with external pressure. The effect is observed to be lanthanide dependent, with the strongest response for Ln = La and the weakest for Ln = Sm. The trend is qualitatively in agreement with our density functional theory calculations. The same calculations allow us to assign a value of 0.68(2)µB to the Fe moment, obtained from an accurate determination of the muon sites. Our data further show that the magnetic lanthanide order transitions do not follow the simple trend of Fe, possibly as a consequence of the different f -electron overlap. [ABSTRACT FROM AUTHOR]

In dc and ac practical applications of MgB[sub2] superconducting wires, an important role is represented by the material sheath that has to provide, among other things, a suitable electrical and thermal stabilization. One way to obtain a large-enough amount of low-resistivity material into the conductor architecture is to use it as the external sheath. In this paper, we study ex situ multifilamentary MgB[sub2] wires fabricated with oxide-dispersion strengthened copper (GlidCop) as the external sheath in order to reach a good compromise between critical current density and thermal properties. We prepared three GlidCop samples with different contents of dispersed submicroscopic Al[sub2]O[sub3] particles. We characterized the superconducting and thermal properties, and we showed that the good thermal conductivity, together with the good mechanical properties and a reasonable critical current density, makes the GlidCop composite wire a useful conductor for applications where high thermal conductivity is required at temperatures above 30 K, such as superconducting fault-current limiters. [ABSTRACT FROM AUTHOR]

The grain size and the grain boundaries play an important role in determining the pinning properties and the current carrying capability of MgB2. Here we present an experimental study on the effect of grain oxidation on the superconducting properties of MgB2 ex-situ Powder-in-Tube (PIT) tapes. We fabricated Fe-sheathed monofilamentary tapes using a variety of powders synthesized in inert (IA) or oxidizing (OA) atmosphere. In order to understand the role of magnesium oxide (MgO) we studied the effect of the presence of the oxidation layer on the field dependence of the critical current density. To this purpose, we developed a process for the powder synthesis and tube filling and sealing in controlled atmosphere to reduce the oxygen contamination; with this process the connectivity of the grains in the final tapes proved to be increased. Then, we introduced a controlled oxidation step. We will show how the presence of the MgO layer enhances the critical current field dependence. High energy X ray diffraction measurements were performed on the samples, and the grain size of the unsintered and sintered powders in the tapes was measured by means of Scanning Electron Microscopy (SEM). The pinning force was studied, and different mechanisms were found for the samples prepared in IA and OA. The different behavior shown by the two different typologies of tapes was correlated with the presence or absence of the MgO layer. [ABSTRACT FROM AUTHOR]

MgB2 monofilamentary nickel-sheathed tapes and wires were fabricated by means of the ex-situ powder-in-tube method using either high-energy ball milled and low temperature synthesized powders. In the first part of the paper it will be shown the effect of milling on tapes realized with powders synthesized at 900 °C. The milling time and the milling revolution speed were tuned in order to maximize the critical current density (Jc) in field: the maximum Jc, value of 6 x 104 A/cm2 at 5K and 4 T was obtained for the tape prepared with powders milled for 144 h at 180 rpm. In the second part of the paper we study the effect of the powders synthesis temperature in a wire configuration. Various synthesis temperature were investigated (730 °C-900 °C) finding a best Jc value for the wire prepared with powders synthesized at 745° C. We speculate that this optimal temperature is due to the fluidifying effect of unreacted magnesium content before the sintering process which could better connect the grains. [ABSTRACT FROM AUTHOR]