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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.

Flukiger R.,University of Geneva | Al Hossain M.S.,University of Geneva | Senatore C.,University of Geneva | Buta F.,University of Geneva | Rindfleisch M.,Hyper Technology Research Inc.
IEEE Transactions on Applied Superconductivity | Year: 2011

By means of Cold High Pressure Densification (CHPD), the critical current density, Jc, of binary and alloyed MgB2 wires has been enhanced by more than a factor 2 at 4.2 K and at fields up to 19 T. The relative MgB2 mass density of binary MgB2 wires was enhanced to ̃54% after applying 2.5 GPa at 300 K before reaction. In C 4H6O5 (malic acid) alloyed wires, densification also caused the enhancement of Birr, as a consequence of a slightly enhanced C content, determined by X ray diffraction. Almost isotropic J c values were obtained for C4H6O5 added wires of 1 × 0.6 mm2 cross section, the values of J c(4.2K) = 1 × 104 A/cm2 for parallel and perpendicular fields being obtained at 13.8 and 13.4 T, respectively (1 μV/cm criterion). The corresponding values for 20 K were both close to 6.2 T. The value of B// irr at 20 K was 11 T. The positive effects of cold densification on Jc and Birr on MgB2 was also observed on 150 mm long wires alloyed with C4H6O 5 (malic acid) or with SiC, by the succession of 6 overlapping pressure steps. This process can be extended to long wire lengths: by means of a newly developed prototype machine with an automatic press/release/ advance sequence, a first wire length of 1 m was densified at 1.5 GPa, yielding J c(4.2 K) = 1 × 104 A/cm2 at 13.1 T. Further improvements are expected after optimization. © 2011 IEEE.

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.

Ghosh A.K.,Brookhaven National Laboratory | Gregory E.,Supergenics LLC i | 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.

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.

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