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Kim J.H.,University of Wollongong | Oh S.,National Fusion Research Institute | Kumakura H.,Japan National Institute of Materials Science | Matsumoto A.,Japan National Institute of Materials Science | And 9 more authors.
Advanced Materials | Year: 2011

High electrical current without dissipation is valuable, not only for power transmission, but also in other fields, such as energy storage or high-field magnets for medical applications. The superconductor magnesium diboride (MgB 2) has a transition temperature of about 40 K [1] and thus can be operated without the need for liquid helium, which is expensive. MgB 2 wire made from inexpensive, clean, starting materials will further accelerate the spread of practical superconductor applications. Here we report on an economical way of producing high-performance MgB 2 wire using carbon-encapsulated boron nanopowder and coarse magnesium powder. It was found that carbon encapsulation suppresses surface oxidation, while nanometer-sized boron can be fully reacted with magnesium at low sintering temperature. Ductile magnesium coarse powders are elongated during the cold-working, leading to alignment of voids and enhanced grain connectivity. As a result, superconducting wires with very high critical current density can be fabricated using inexpensive starting materials. Hints for overcoming major obstacles that have been discussed over the past decade can be found, and further improvements are also expected. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ghosh A.K.,Brookhaven National Laboratory | Gregory E.,Supergenics I LLC | Peng X.,Hyper Technology Research Inc.
IEEE Transactions on Applied Superconductivity | Year: 2011

High-Jc Nb3Sn strands often exhibit instabilities in 4.2 K liquid helium at low fields ∼0.5 to 3 T which are associated with magnetization flux-jumps. However at 1.9 K in superfluid helium, a minimum in premature quench currents at intermediate fields of 5 to 7 T has been observed in voltage-current measurements. These measurements are typically used for critical current determinations, and the premature quenching is driven by current redistribution within the strand as the current is increased and is termed "self-field" instability. In this paper, the magnetization and self-field stability of Nb3Sn strands with Jc ∼ 2000 A/mm at 12 T are described for a series of wires made using the Sn-tube approach with filament diameters ranging from 13 to 65 μm. The copper stabilizer of these wires after reaction has residual resistivity ratio, RRR, of ∼5, which in effect means that any dynamic stabilization from thermal conduction effects is negligible. In this regime of RRR, we find that the magnetization stability with transport current increases with decreasing filament diameter as predicted by simple adiabatic theory. We also observed that at 4.2 K the self-field stability improved with decreasing filament size, but became worse with decreasing temperature as seen in measurements at 2.0 K. © 2010 IEEE.

Susner M.A.,Ohio State University | Daniels T.W.,Ohio State University | Daniels T.W.,University of Pittsburgh | Sumption M.D.,Ohio State University | And 3 more authors.
Superconductor Science and Technology | Year: 2012

Monocore powder-in-tube MgB 2 precursor strands were cold-drawn and heat-treated at 600 and 700°C for times of up to 71h, and structureproperty relationships examined. Drawing induced elongation of the Mg particles led, after heat treatment (HT), to a textured macrostructure consisting of elongated fine polycrystalline MgB 2 fibers (or veins) separated by elongated pores. The superconducting transition temperature (T c), critical current density (J c) and bulk pinning force density (F p) were correlated with the macrostructure and grain size. Grain size increased with HT time at both 600 and 700°C. Critical current density and hence F p decreased monotonically but not linearly with grain size. Overall, it was observed that at 700°C the MgB 2 reaction was more or less complete after as little as 30min; at 600°C full reaction completion did not occur until 72h into the HT. Transport, J ct(B), was measured in a perpendicular applied field, and the magnetic critical current densities, J ⊥ cm(B)and J φ cm(B), were measured in perpendicular and parallel (axial) applied fields, respectively. Particularly noticeable was the premature drop-off of at fields well below the irreversibility field of J ct(B). This effect is attributed to the fibrous macrostructure and its accompanying anisotropic connectivity. Magnetic measurements with the field directed along the strand axis yielded a critical density, J ⊥ cm(B) , for current flowing transversely to the strand axis that was less than, and dropped off more rapidly than, J ct(B). In the conventional magnetic measurement, the loop currents that support the magnetization are restricted by the lower of J ct(B) and J φ cm(B): in the present case the latter, leading to the premature drop-off of the measured compared to J ct(B) with increasing field. This result is supported by Kramer plots of the J φ cm(B) and J ct(B) data, which lead to an irreversibility field for transverse current that is very much less than the usual transport-measured longitudinal one, B irr,t. © 2012 IOP Publishing Ltd.

Xu X.,Ohio State University | Sumption M.D.,Ohio State University | Bhartiya S.,Ohio State University | Peng X.,Hyper Technology Research Inc. | Collings E.W.,Ohio State University
Superconductor Science and Technology | Year: 2013

In this work, the transport and magnetization properties of distributed barrier rod-in-tube (RIT) strands and tube type strands are studied. While tube type strands had smaller magnetizations and thus better stabilities in the low-field region, their 12 T non-Cu Jc values were somewhat smaller than those of the RIT strands. Microstructures were investigated in order to find out the reasons for the difference in non-Cu Jc values. Their grain size and stoichiometry were found to be comparable, leading to similar layer Jc values. Accordingly it was determined that the lower A15 area fraction rather than the quality of the A15 layer was the cause of the discrepancy in non-Cu Jc. Subsequently, the area utilizations of subelements were investigated. While for a RIT strand the fine grain (FG) A15 area occupies ∼60% of a subelement, for a tube type strand it is no more than 40%. Further analysis indicates that the low FG area fraction in a tube type strand is attributed to its much larger unreacted Nb area fraction. Finally, a simple change in strand architecture is proposed to reduce the unreacted Nb area fraction. © 2013 IOP Publishing Ltd.

Susner M.A.,Ohio State University | Yang Y.,Ohio State University | Sumption M.D.,Ohio State University | Collings E.W.,Ohio State University | And 3 more authors.
Superconductor Science and Technology | Year: 2011

Conventional doping methods that directly add C or a C-bearing species to Mg + B powder have the disadvantage of adding C inhomogeneously, yielding either under-reacted regions or, in some cases, secondary phases which may be either beneficial or detrimental. Alternatively, pre-doped B powder provides a more homogeneous distribution of the C dopant in MgB2. In this work, powders containing varying amounts of C were used to produce in situ MgB 2 strands which showed high values of Bc2, Birr and transport Jc (104 A cm-2 at 13.3 T). Compared to SiC-added and malic-acid-treated strands the pre-doped MgB2 showed high values of Birr primarily due to more efficient C substitution into the B sublattice and a concomitant increase in transport Jc. © 2011 IOP Publishing Ltd.

Xu X.,Ohio State University | Sumption M.D.,Ohio State University | Peng X.,Hyper Technology Research Inc.
Advanced Materials | Year: 2015

Nb3Sn strands fabricated using Nb-Zr alloy, can be internally oxidized, provided that oxygen is properly supplied via an oxide powder. This allows the formation of fine intragranular and intergranular ZrO2 particles in a Nb3Sn matrix. These particles can refine the grain size by a factor of three and thereby greatly enhance the Nb3Sn critical current density. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Xu X.,Ohio State University | Sumption M.,Ohio State University | Peng X.,Hyper Technology Research Inc. | Collings E.W.,Ohio State University
Applied Physics Letters | Year: 2014

In this Letter, we demonstrate that if oxygen can be properly supplied to (Nb-Zr)-Sn wires, ZrO2 precipitates will form during the heat treatment, refining the Nb3Sn grain size markedly. Here, a Nb 3Sn subelement was fabricated in which Nb-1Zr alloy was used, and oxygen was supplied via SnO2 powder. The results showed that such a design could supply sufficient oxygen to internally oxidize the Zr in the Nb-1Zr alloy, and that the sample reacted at 650 C had grain sizes of ∼45 nm, less than half the size of the grains in present Nb3Sn conductors. Magnetic measurements showed that the peak of the pinning force vs. field (Fp-B) curve was shifted to ∼0.3Birr (the irreversibility field). © 2014 AIP Publishing LLC.

Li G.Z.,Ohio State University | Sumption M.D.,Ohio State University | Rindfleisch M.A.,Hyper Technology Research Inc. | Thong C.J.,Hyper Technology Research Inc. | And 2 more authors.
Applied Physics Letters | Year: 2014

A series of MgB2superconducting composite strands co-doped with Dy2O3and C was prepared via an advanced internal Mg infiltration (AIMI) route. The transport properties and MgB2layer growth were studied in terms of the Dy2O3doping level, reaction temperature, and reaction time. Transport studies showed that both critical current densities, Jcs, and irreversibility fields, Birrs, were increased with Dy2O3doping. The highest layer Jcwas 1.35 × 105A/cm2at 4.2 K, 10 T, 30% higher than that of the best AIMI wires without Dy2O3doping. The highest "non-barrier" Jcreached 3.6 × 104A/cm2at 4.2 K, 10 T, which was among the best results reported so far. The improvements were even more pronounced at higher temperatures where the field at which the layer Jcreached 104A/cm2was pushed out by 0.9 T at 20 K, 1.2 T at 25 K, and 1.4 T at 30 K. While little or no enhancement in Birrwas seen at 10 K and 15 K, the increases in Jcat higher temperatures were consistent with observed increases in Birrof 17% at 20 K, 44% at 25 K, and 400% at 30 K. Also, there were some indications that the reaction and layer growth of MgB2were enhanced by Dy2O3doping. © 2014 AIP Publishing LLC.

Agency: Department of Energy | Branch: | Program: SBIR | Phase: Phase II | Award Amount: 1.00M | Year: 2016

Superconducting Wire Technologies for Magnets. The need is for strands that operate at a minimum of 12 Tesla (T) field, with preference for production scale (> 3 km continuous lengths) wire technologies at 15 to 25 T. The strands are preferred to have higher engineering current densities, at least 400 amperes per square millimeter of strand cross section at the target field of operation and 4.2 K temperature, and have reduced effective filament diameter, in particular to less than 30 micrometers at 1 mm wire diameter, with minimal concomitant reduction of the thermal conductivity of the stabilizer or strand critical density. Hyper Tech has fabricated Nb3Sn strands with our tube approach strand with 200900 filaments at 0.7 mm OD in kilometer lengths. While the deff sizes and stabilities of these strands are excellent, and the conductor performance is very good at 2500 A/mm2 at 12 T, it would be very useful for HEP applications to push the nonCu Jc in these strands with high filament counts way beyond the 3000 + A/mm2 12T4.2K level (potential for 50% plus improvement over today’s commercial wires). GenIenr aPlh Sastaet eI,m wene ts oufc cheoewd etdh iisn p mroabkleinmg issu bbeeilnegm aendtdsr easnsde dr estacks with refined grain size in the reacted Nb3Sn superconductors. We have made 61subelement Nb1%Zr restack strands and drew them down to diameters of 0.7 mm, 0.5 mm, 0.4 mm and 0.25 mm with sub element size of 65 m, 45m, 35 m and 25m respectively. We obtained both magnetic and transport layer Jc of 10,000 A/mm2 at 12T4.2K in the binary Nb3Sn with ZrO2 in sub element. For the proposed Phase II program, we will first optimize the heat treatment schedule of the restack wires made in Phase I, and then further optimize the chemistry in the sub element. We will make 217 Sub element restack strands using the optimized sub elements and draw strands down to 0.7 mm diameter with sub element size of 35 m. We will demonstrate strand variants for easy ternary alloying. Through this Phase II, we will fabricate strands targeting to obtain a 50% Je performance of the best presently available commercial conductors at 15 T and 16T. Commercial applications and other benefits The success of this SBIR will lead to a Nb3Sn superconductors for next generation accelerators, fusion reactors, and medical applications such as NMR, MRI, and accelerators for medical purposes. Key Words 3Sn, Ternary Nb3Sn, TubeType, deff, NonCu Jc SumTmhiasr yp rfoogrr mamem pbuerrssu eosf tchoen gdreevsesl opment of improved Nbare used for understanding physics, and various computer and3 Smne cdoicnadlu acptoprlisc afotiro nasc.

Li G.Z.,Ohio State University | Sumption M.D.,Ohio State University | Susner M.A.,Ohio State University | Yang Y.,Ohio State University | And 5 more authors.
Superconductor Science and Technology | Year: 2012

Recent advances in MgB 2 conductors are leading to a new level of performance. Based on the use of proper powders, proper chemistry, and an architecture which incorporates internal Mg diffusion, a dense MgB 2 structure with not only a high critical current density J c, but also a high engineering critical current density, J e, can be obtained. In this paper, a series of these advanced (or second generation, 2G) conductors has been prepared. Scanning electron microscopy and associated energy dispersive x-ray spectroscopy were applied to characterize the microstructures and compositions of the wires, and a dense MgB 2 layer structure was observed. The best layer J c for our sample is 1.07×10 5Acm 2 at 10T, 4.2K, and our best J e is seen to be 1.67×10 4Acm 2 at 10T, 4.2K. Optimization of the transport properties of these advanced wires is discussed in terms of the B powder choice, area fraction, and MgB 2 layer growth mechanism. © 2012 IOP Publishing Ltd.

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