E. W. Collings

The Ohio State University, Columbus, Ohio, United States

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Publications (272)311.15 Total impact

  • X Xu, M D Sumption, E W Collings
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    ABSTRACT: The impacts of heat treatment (HT) temperature and Ti doping on low-field flux jumping and 12 T Jc of high-performance internal-Sn, distributed barrier (Nb-Ta)3Sn strands have been explored. It was found that higher HT temperatures could suppress low-field flux jumps by not only reducing the Jc (B) curve slope, but also increasing the heat capacity and decreasing the dJc /dT. A metric, Jc,3 T/Jc,12 T (the ratio of 3 T to 12 T Jc ), was used to describe the slope of the Jc (B) curve. In addition, an analytical equation was derived to predict the amplitude of a flux jump. The Jc (B) curves were further analyzed in the form of Kramer plots to extract the irreversibility field, Birr, and the maximum bulk pinning forces, Fp,max. The variations of Birr, Fp,max and grain size, d, with HT and Ti doping were also analyzed. Fp,max initially increasing linearly with 1/d, saturated at small values of d, possibly because the grains became columnar.
    Superconductor Science and Technology 08/2014; 27(9):095009. · 2.76 Impact Factor
  • M A Susner, M D Sumption, A Takase, E W Collings
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    ABSTRACT: In an investigation of possible atomic substitution for the Mg site in MgB2, superconducting thin films were deposited by pulsed laser deposition using MgB2 and ZrB2 targets. The resulting c-axis-oriented thin films contained various concentrations of Zr. The structural, chemical, and superconductive properties of these films were investigated. ZrB2 additions were found to increase the a lattice parameter; STEM-based chemical analysis showed Zr to be present within the grains. The superconducting critical temperature was suppressed for the heavily-doped samples. These observations are strong evidence for the substitution of Zr for Mg in the Mg sublattice of MgB2.
    Superconductor Science and Technology 06/2014; 27(7):075009. · 2.76 Impact Factor
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    ABSTRACT: We have used high-pressure, high-temperature synthesis at 1500-1700 °C and 10 MPa to create homogeneously C-substituted MgB2 from a B4C + Mg mixture. X-ray diffraction analysis showed large peak-shifts consistent with a decrease in the a lattice parameter for the B4C-derived MgB2 as compared to an undoped sample (0.033-0.037 Å, depending on the sample). Microstructural investigation showed a three-phase mixture in the B4C-derived ingots: MgB2-xCx (with 0.178 < x < 0.195), MgB2C2, and Mg. The carbon concentration determined from the lattice parameter shift (5.95 at. %) matched well with the calorimetrically derived concentration of 5.3-5.8 at. % C. Furthermore, the carbon content measured by electron probe micro-analysis was shown to be 6.2 ± 1.3 at. %. Finally, we performed bulk specific heat measurements to determine the homogeneity of C-doping in the MgB2. The width of the Tc distribution for the C-doped MgB2 was only 3-6 K with a full-width half maximum (FWHM) of 1.4 K, compared to a width of 2.5 K and a FWHM of 0.65 for an undoped sample. The consistency of these three measurements on a large-grained homogeneous material is unambiguously supportive of C-substitution.
    03/2014; 104(16).
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    X. Xu, M. Sumption, X. Peng, E. W. Collings
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    ABSTRACT: 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 Nb3Sn 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 {\deg}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).
    Applied Physics Letters 02/2014; 104(8). · 3.79 Impact Factor
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    ABSTRACT: We have studied thermodynamic phase stability in the Mg–B system through use of a high-pressure, high-temperature apparatus consisting of a large pressure vessel and an RF induction heater. The incongruent melting temperature for MgB2 was found to be ∼1450 °C at 10 MPa using thermal analysis data applied to both MgB2 powder samples and Mg/B mixtures. The experimental temperature is ∼300 °C lower than temperatures shown in calculated phase diagrams of the Mg–B system at the same pressure and the discrepancy demonstrates the need for further experimental investigations of phase stability in binary Mg–B and ternary Mg–B–X systems. In this study C (as an impurity in boron) was found to have a large effect on the peritectic temperature, with a relatively small (0.7 wt% C) impurity concentration resulting in a ∼40 °C elevation of the peritectic temperature. Along with morphological characterization, XRD and EPMA analyses were used to identify phases and confirm the peritectic transformation in the Mg–B phase diagram.
    Thermochimica Acta 01/2014; 576:27–35. · 1.99 Impact Factor
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    ABSTRACT: In this paper, we report the properties of two tube type Ta doped Nb3Sn strands: one strand was additionally Ti doped by way of a Sn-Ti alloy core, and the other had high Cu/Sn ratio within the filaments. Higher irreversibility field (Birr) was obtained on the quaternary strand with respect to the (Nb-7.5 wt.%Ta)3Sn strand. High Cu/Sn ratio decreased the amount of coarse grain formation, but also degraded the layer Jc of the tube type strand by depressing the Sn content in the fine grain (FG) layer. A new type of strand, the subelement of which is composed of seven bare Cu-Sn cored Nb tube filaments, was designed with the aim to reduce the unreacted Nb area fractions. The test results of the first experimental strand are reported. The unreacted Nb ratio is reduced relative to normal tube type strands and the FG area fraction is improved. The unique structure of this strand makes it also possible to improve the stoichiometry of FG and reduce the effective diameter (deff) .
    IEEE Transactions on Applied Superconductivity 01/2014; 24(3):1-4. · 1.20 Impact Factor
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    ABSTRACT: One of the goals of the Large Hadron Collider Accelerator Research Program (LARP) is to demonstrate the feasibility of Nb3Sn technology for a proposed luminosity upgrade based on large aperture high gradient quadrupole (HQ) magnets. For such magnets, field quality at the bore is a critical requirement for which reason the parasitic magnetization of the windings must be reduced to manageable limits. In other words, it is necessary to minimize 1) the static intrastrand persistent-current magnetization of the cable and 2) the cable's coupling magnetization caused by coupling currents passing through interstrand contact resistance during field ramping. This report focuses on persistent-current magnetization as measured by vibrating-sample magnetometry on pieces of strand removed from a section of heat treated HQ cable.
    IEEE Transactions on Applied Superconductivity 01/2014; 24(3):1-5. · 1.20 Impact Factor
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    ABSTRACT: A series of high-performing continuous-tube-filling-forming-fabricated (CTFF) powder-in-tube-type (PIT) MgB2 strands have been prepared, with critical current densities, Jcs, higher than 1.30×105 A/cm2 and n-values above 30 at 4.2 K, 5 T. The transport Jcs and corresponding n-values of a selected sample C1 were reported at temperatures, T, of 4.2-30 K and magnetic fields, B, of 0-12 T. The Jc - B data were fitted by Eisterer's percolation model and the temperature dependences of the fitting parameters were analyzed. The n - Jc curves showed a power law relationship n∞Jcm, also previously observed in state-of-the-art monocore MgB2 wires. Further analysis revealed that, like monofilamentary wires, the n(B, T) of this multifilamentary strand can also be estimated for all B and T based on the results of transport voltage-current (V- I) measurements made at one arbitrarily chosen temperature.
    IEEE Transactions on Applied Superconductivity 01/2014; 24(3):1-5. · 1.20 Impact Factor
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    ABSTRACT: A dc transport current was applied to the strands of a Roebel cable at 77 K in liquid nitrogen bath. The inter-strand contact resistance was measured. It was modified either by applying a pressure on the cable at 77 K in liquid nitrogen bath or using different soldering patterns between the strands of the cable. Magnetization ac losses were measured in frequency range 50-200 Hz in applied magnetic field 4-70 mT perpendicular to the broader face of the cable to test the inter-strand contact resistance effect. High stability and very low level of coupling losses were observed in the cables even with the lowest inter-strand resistances.
    IEEE Transactions on Applied Superconductivity 01/2014; 24(3):1-5. · 1.20 Impact Factor
  • X. Xu, M. D. Sumption, E. W. Collings
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    ABSTRACT: In this work, an analytic model for phase formation and volume expansion during heat treatment in tube type Nb3Sn strands is presented. Tube type Nb3Sn conductors consist of Nb or Nb-Ta alloy tube with a simple Cu/Sn binary metal insert to form the basic subelement (filament). A number of these elements, each with an outer Cu jacket, are restacked to form a multifilamentary strand. The present tube type conductors, with 4.2 K, 12 T non-Cu critical current density (Jc) in the 2000-2500 A mm-2 range and effective subelement diameters (deff) in the 12-36 μm range, are of interest for a number of applications. During the reaction of typical tube type strands, the Sn-Cu becomes molten and reacts with the Nb tube first to form NbSn2, then Nb6Sn5. At later times in the reaction sequence, all of the NbSn2 and Nb6Sn5 is converted to Nb3Sn. Some of the Nb3Sn is formed by a Nb-Sn reaction and has a fine grain (FG) structure, while some is converted from Nb6Sn5, which results in a coarse grain (CG) region. The fractions of FG and CG A15 are important in determining the final conductor properties. In this work we develop an analytic model to predict the radial extents of the various phases, and in particular the final FG and CG fractions based on the starting Nb, Cu, and Sn amounts in the subelements. The model is then compared to experimental results and seen to give reasonable agreement. By virtue of this model we outline an approach to minimize the CG regions in tube type and PIT strands and maximize the final FG area fractions. Furthermore, the volume change during the various reaction stages was also studied. It is proposed that the Sn content in the Cu-Sn alloy has a crucial influence on the radial expansion.
    Superconductor Science and Technology 12/2013; 26(12):5006-. · 2.76 Impact Factor
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    ABSTRACT: An advanced internal Mg infiltration method (AIMI) in this paper has been shown to be effective in producing superconducting wires containing dense MgB2 layers with high critical current densities. In this study, the in-field critical current densities of a series of AIMI-fabricated MgB2 strands were investigated in terms of C doping levels, heat treatment (HT) time and filament numbers. The highest layer Jc for our monofilamentary AIMI strands is 1.5 x 10^5 A/cm2 at 10 T, 4.2 K, when the C concentration was 3 mol% and the strand was heat-treated at 675 {\deg}C for 4 hours. Transport critical currents were also measured at 4.2 K on short samples and one-meter segments of eighteen-filament C-doped AIMI strands. The layer Jcs reached 4.3 x 10^5 A/cm2 at 5 T and 7.1 x 10^4 A/cm2 at 10 T, twice as high as those of the best PIT strands. The analysis of these results indicates that the AIMI strands, possessing both high layer Jcs and engineering Jes after further optimization, have strong potential for commercial applications.
    Superconductor Science and Technology 07/2013; 26(9). · 2.76 Impact Factor
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    ABSTRACT: We notice that when MgB2 is doped so as to increase its Birr and Bc2, the low-field Jc is decreased.We propose that this phenomenon is intrinsic to superconductors with a large variability in Bc2.Using the surface pinning function, we have shown that increases in Bc2 will decrease low-B Jc.For an application where low-B Jc needs to be maximized, doping will be deleterious.Rather, increases in connectivity should be explored.
    Physica C Superconductivity 07/2013; · 0.72 Impact Factor
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    IEEE Transactions on Applied Superconductivity 06/2013; 23(3). · 1.20 Impact Factor
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    X Xu, M D Sumption, S Bhartiya, X Peng, E W Collings
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    ABSTRACT: 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 Jcs 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 Jcs. Accordingly it was determined that the lower A15 area fraction rather than the quality of 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.
    Superconductor Science and Technology 04/2013; 26(7). · 2.76 Impact Factor
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    ABSTRACT: We present a design and details of construction of two calorimetric systems that allow us to measure the total loss in high temperature superconducting coils or linear samples carrying alternating current while exposed to a strong alternating magnetic field. This measurement technique is based on the boil-off of liquid nitrogen. The first system is designed to measure ac losses in superconducting coils in self-field generated by AC transport current. The second system contains a permanent magnet rotor and simulates the environment of an electric motor or generator. The sensitivity of the system is such that it can measure low losses from a few milliwatts to several hundred milliwatts, in either a static or dynamic magnetic field.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):4701505-4701505. · 1.20 Impact Factor
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    ABSTRACT: ISI Document Delivery No.: 143VA
    IEEE Transactions on Applied Superconductivity 01/2013; 23:5. · 1.20 Impact Factor
  • H.S. Kim, M.D. Sumption, H. Lim, E.W. Collings
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    ABSTRACT: The plastic constitutive equation of tubular materials under hydraulic pressure needs to be determined for the successful application of hydroforming technique to the seamless fabrication of multicell superconducting radiofrequency cavities. This paper provides the empirical constitutive properties of tubular material determined by tensile and hydraulic bulge tests. During an experimental bulge test, the internal pressure, bulge height and wall thickness were continuously measured. Based on this data, the flow stress curves were calculated using an analytical model. From the obtained flow stress curves, numerical simulations were performed, and the resulting bulge heights and wall thicknesses obtained were compared with the experimental results to verify the procedure.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):3500604-3500604. · 1.20 Impact Factor
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    ABSTRACT: Unlike the known isoelectronic undoped intrinsic FeAs compounds, LiFeAs does not show any spin-density wave behavior but exhibits superconductivity at ambient pressures without chemical doping. It has a superconducting transition temperature, Tc, of 18 K with electron-like carriers and a very high 0 K upper critical magnetic field, Bc2(0), of greater than 80 T making the compound suitable for many high magnetic field applications at cryogenic temperatures. Oxypnictide materials are known for a complexity of their methods of preparation. The reported methods of LiFeAs preparation are based on the solid-state reaction at high temperatures (740 °-1050 °C) for long times (24-60 h). In the present work a simple electrochemical route is proposed for the preparation of a pnictide LiFeAs superconductor. During electrolysis, Li ions in the electrolyte become inserted into the FeAs lattice to form LiFeAs on the surface of the FeAs electrode. The proposed method differs from the existing electrochemical method and also from the traditional high temperature solid-state reaction methods. It is promising for the preparation of LiFeAs bulks and large scale LiFeAs films or tapes for various electric power or high magnetic field applications at cryogenic temperatures.
    IEEE Transactions on Applied Superconductivity 01/2013; 23(3):7300204-7300204. · 1.20 Impact Factor
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    ABSTRACT: Intra-wire resistance and AC loss of various multi-filamentary MgB2 wires with filaments surrounded by Nb barriers have been measured and analyzed. The intra-wire resistance is measured with a direct four-probe voltage–current method at various temperatures. The AC loss is acquired by both vibrating sample magnetometer (VSM) and magnetization measurements at 4.2 K. With the aid of finite element method simulations, the filament-to-matrix contact resistance and effective transverse resistivity are derived from direct intra-wire resistance measurements. The effective transverse resistivity values are in good agreement with those analytically derived from the AC coupling loss measurements. Surprisingly, very high values of filament-to-matrix contact resistivity are found, being 2 or 3 orders higher than commonly found for NbTi or Nb3Sn wires.
    Superconductor Science and Technology 12/2012; 26(2):025002. · 2.76 Impact Factor
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    ABSTRACT: Cu sheathed polycrystalline Ba0.6K0.4Fe2As2 superconducting wire was prepared by a two-step powder-in-tube method. A pressure of 2 GPa was applied to a short sample before heat treatment. Magnetization and transport measurements were performed to investigate the effects of cold high pressure densification on the microstructure and superconductivity. The cold pressed sample shows an improved self-field transport critical current density of 2.8 × 104 A/cm2 (Ic = 83 A) at 4.2 K, which is nearly as twice as the unpressed sample. However, both samples manifest pronounced weak-link behavior, suggesting the technique need to be further optimized. The comparison of properties between pressed and unpressed sample and related mechanism was discussed.
    Physica C Superconductivity 12/2012; 483:13–16. · 0.72 Impact Factor

Publication Stats

1k Citations
311.15 Total Impact Points

Institutions

  • 1995–2014
    • The Ohio State University
      • Department of Materials Science and Engineering
      Columbus, Ohio, United States
  • 2011
    • Southeast University (China)
      Nan-ching-hsü, Jiangxi Sheng, China
  • 1995–2007
    • University of Wollongong
      • Institute for Superconducting and Electronic Materials
      Wollongong, New South Wales, Australia
  • 2005
    • Kagoshima University
      Kagosima, Kagoshima, Japan
  • 1969–1995
    • Battelle Memorial Institute
      • Department of Physics
      Columbus, Ohio, United States
  • 1991
    • Iowa State University
      Ames, Iowa, United States
  • 1972–1975
    • Wichita State University
      Wichita, Kansas, United States