E. W. Collings

The Ohio State University, Columbus, Ohio, United States

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Publications (322)382.56 Total impact

  • Source
    H.S. Kim · M.D. Sumption · M.A. Susner · H. Lim · E.W. Collings
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    ABSTRACT: The heat treatment, tensile testing, and bulge testing of Cu and Nb tubes has been carried out to gain experience for the subsequent hydroforming of Nb tube into seamless superconducting radio frequency (SRF) cavities for high energy particle acceleration. In the experimental part of the study samples removed from representative tubes were prepared for heat treatment, tensile testing, residual resistance ratio measurement, and orientation imaging electron microscopy (OIM). After being optimally heat treated Cu and Nb tubes were subjected to hydraulic bulge testing and the results analyzed. In the final part of the study finite-element models (FEM) incorporating constitutive (stress-strain) relationships analytically derived from the tensile and bulge tests, respectively, were used to replicate the bulge test. As expected, agreement was obtained between the experimental bulge parameters and the FEM model based on the bulge-derived constitutive relationship. Not so for the FEM model based on tensile-test data. It is concluded that a constitutive relationship based on bulge testing is necessary to predict a material's performance under hydraulic deformation.
    Full-text · Article · Dec 2015
  • Y. Yang · G. Li · M. Susner · M.D. Sumption · M. Rindfleisch · M. Tomsic · E.W. Collings
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    ABSTRACT: The influences of strand twisting and bending (applied at room temperature) on the critical current densities, Jc, and n-values of MgB2 multifilamentary strands were evaluated at 4.2 K as function of applied field strength, B. Three types of MgB2 strand were evaluated: (i) advanced internal magnesium infiltration (AIMI)-processed strands with 18 filaments (AIMI-18), (ii) powder-in-tube (PIT) strands processed using a continuous tube forming and filling (CTFF) technique with 36 filaments (PIT-36) and (iii) CTFF processed PIT strands with 54 filaments (PIT-54). Transport measurements of Jc(B) and n-value at 4.2 K in fields of up to 10 T were made on: (i) PIT-54 after it was twisted (at room temperature) to twist pitch values, Lp, of 10-100 mm. Transport measurements of Jc(B) and n-value were performed at 4.2 K; (ii) PIT-36 and AIMI-18 after applying bending strains up to 0.6% at room temperature. PIT-54 twisted to pitches of 100 mm down to 10 mm exhibited no degradation in Jc(B) and only small changes in n-value. Both the Jc(B) and n-value of PIT-36 were seen to be tolerant to bending strain of up to 0.4%. On the other hand, AIMI-18 showed ±10% changes in Jc(B) and significant scatter in n-value over the bending strain range of 0-0.6%.
    No preview · Article · Oct 2015 · Physica C Superconductivity
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    ABSTRACT: High quality, c-axis oriented, MgB 2 thin films were successfully grown on 6H-SiC substrates using pulsed laser deposition (PLD) with subsequent in situ annealing. To obtain high purity films free from oxygen contamination, a dense Mg–B target was specially made from a high temperature, high pressure reaction of Mg and B to form large-grained (10–50 m) MgB 2. Microstructural analysis via electron microscopy found that the resulting grains of the film were composed of ultrafine columnar grains of 19–30 nm. XRD analysis showed the MgB 2 films to be c-axis oriented; the a-axis and c-axis lattice parameters were determined to be 3.073 ± 0.005Å and 3.528 ± 0.010Å, respectively. The superconducting critical temperature , T c,onset , increased monotonically as the annealing temperature was increased, varying from 25.2 K to 33.7 K. The superconducting critical current density as determined from magnetic measurements, J cm , at 5 K, was 10 5 A/cm 2 at 7.8 T; at 20 K, 10 5 A/cm 2 was reached at 3.1 T. The transport and pinning properties of these films were compared to " powder-in-tube " (PIT) and " internal-infiltration " (AIMI) processed wires. Additionally, examination of the pinning mechanism showed that when scaled to the peak in the pinning curve, the films follow the grain boundary, or surface, pinning mechanism quite well, and are similar to the response seen for C doped PIT and AIMI strands, in contrast to the behavior seen in undoped PIT wires, in which deviations are seen at high b (b = B/B c2). On the other hand, the magnitude of the pinning force was similar for the thin films and AIMI conductors, unlike the values from connectivity-suppressed PIT strands.
    Full-text · Article · Sep 2015 · Applied Surface Science
  • G.Z. Li · M.D. Sumption · E.W. Collings
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    ABSTRACT: Significantly enhanced critical current density (Jc) for MgB2 superconducting wires can be obtained following the advanced internal Mg infiltration (AIMI) route. But unless suitable precautions are taken, the AIMI-processed MgB2 wires will exhibit incomplete MgB2 layer formation, i.e. reduced superconductor core size and hence suppressed current-carrying capability. Microstructural characterization of AIMI MgB2 wires before and after the heat treatment reveals that the reaction mechanism changes from a “Mg infiltration-reaction” at the beginning of the heat treatment to a “Mg diffusion-reaction” once a dense MgB2 layer is formed. A drastic drop in the Mg transport rate from infiltration to diffusion causes the termination of the MgB2 core growth. To quantify this process, a two-stage kinetic model is built to describe the MgB2 layer formation and growth. The derived kinetic model and the associated experimental observations indicate that fully reacted AIMI-processed MgB2 wires can be achieved following the optimization of B particle size, B powder packing density, MgB2 reaction activation energy and its response to the additions of dopants.
    No preview · Article · Sep 2015 · Acta Materialia
  • M Majoros · M D Sumption · E W Collings · N J Long

    No preview · Article · Aug 2015 · Superconductor Science and Technology
  • Source
    G Z Li · ⇑ Sumption · E W Collings
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    ABSTRACT: Significantly enhanced critical current density (J c) for MgB 2 superconducting wires can be obtained following the advanced internal Mg infiltration (AIMI) route. But unless suitable precautions are taken, the AIMI-processed MgB 2 wires will exhibit incomplete MgB 2 layer formation, i.e. reduced superconduc-tor core size and hence suppressed current-carrying capability. Microstructural characterization of AIMI MgB 2 wires before and after the heat treatment reveals that the reaction mechanism changes from a ''Mg infiltration-reaction'' at the beginning of the heat treatment to a ''Mg diffusion-reaction'' once a dense MgB 2 layer is formed. A drastic drop in the Mg transport rate from infiltration to diffusion causes the termination of the MgB 2 core growth. To quantify this process, a two-stage kinetic model is built to describe the MgB 2 layer formation and growth. The derived kinetic model and the associated experimental observations indicate that fully reacted AIMI-processed MgB 2 wires can be achieved following the optimization of B particle size, B powder packing density, MgB 2 reaction activation energy and its response to the additions of dopants.
    Full-text · Article · Jun 2015 · Acta Materialia
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    ABSTRACT: Persistent magnetization currents are induced in superconducting filaments during the current ramping in magnets. The resulting perturbation to the design magnetic field leads to field quality degradation, particularly at low field, where the effect is stronger relative to the main field. The effects observed in NbTi accelerator magnets were reproduced well with the critical-state model. However, this approach becomes less accurate for the calculation of the persistent-current effects observed in Nb3Sn accelerator magnets. Here, a finite-element method based on the measured strand magnetization is validated using three state-of-the-art Nb3Sn accelerator magnets featuring different subelement diameters, conductor critical currents, magnet designs, and test temperatures. The temperature dependence of the persistent-current effects is reproduced. Based on the validated model, the impact of conductor design on the persistent-current effects is discussed. The strengths, limitations, and possible improvements of the approach are also discussed.
    Full-text · Article · Jun 2015 · IEEE Transactions on Applied Superconductivity
  • Source
    X. Xu · M. Majoros · M.D. Sumption · E.W. Collings
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    ABSTRACT: For many accelerator magnets field quality at the bore is a critical requirement for which reason it is necessary to fully characterize the persistent-current magnetization of strands of the kind under consideration for these magnets. The magnetization of a strand is generally measured in a magnetometer. However, certain effects can differentiate such measurements from the true magnetizations of strands in magnets. This report focuses on persistent-current magnetization: 1) measured by vibrating-sample magnetometer on segments of strand extracted from a section of heat treated $hbox{Nb}_{3}hbox{Sn} $ cable as functions of angle of the applied field, and 2) calculated as function of applied transport current. It is found that the magnetization of a strand in a cable increases by $sim$10% as the field applied to the cable is shifted from edge-on to face-on, and that the difference between the current-on and current-off magnetizations is not significant until close to the operational field of a magnet.
    Full-text · Article · Jun 2015 · IEEE Transactions on Applied Superconductivity
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    ABSTRACT: The coupling magnetization of a Rutherford cable is inversely proportional to an effective interstrand contact resistance Reff, a function of the crossing-strand resistance Rc, and the adjacent strand resistance Ra. In cored cables, Reff continuously varies with W, the core width expressed as percent interstrand cover. For a series of un-heat-treated stabrite-coated NbTi LHC-inner cables with stainless-steel (SS, insulating) cores, Reff (W) decreased smoothly as W decreased from 100%, whereas for a set of research-wound SS-cored Nb3Sn cables, Reff plummeted abruptly and remained low over most of the range. The difference is due to the controlling influence of Rc - 2.5 μΩ for the stabrite/NbTi and 0.26 μΩ for Nb3Sn. The experimental behavior was replicated in the Reff (W )'s calculated by the program CUDI, which (using the basic parameters of the QXF cable) went on to show in terms of decreasing W that: 1) in QXF-type Nb3Sn cables (Rc = 0.26 μΩ), Reff dropped even more suddenly when the SS core, instead of being centered, was offset to one edge of the cable; 2) Reff decreased more gradually in cables with higher Rc's; and 3) a suitable Reff for a Nb3Sn cable can be achieved by inserting a suitably resistive core rather than an insulating (SS) one.
    No preview · Article · Jun 2015 · IEEE Transactions on Applied Superconductivity
  • M Majoros · M D Sumption · E W Collings · N J Long
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    ABSTRACT: A Roebel cable, one twist pitch long, was modified from its as-received state by soldering copper strips between the strands to provide inter-strand connections enabling current sharing. Various DC transport currents (representing different percentages of its critical current) were applied to a single strand of such a modified cable at 77 K in a liquid nitrogen bath. Simultaneous monitoring of I–V curves in different parts of the strand as well as in its interconnections with other strands was made using a number of sensitive Keithley nanovoltmeters in combination with a multi-channel high-speed data acquisition card, all controlled via LabView software. Current sharing onset was observed at about 1.02 of strand I c. At a strand current of 1.3I c about 5% of the current was shared through the copper strip interconnections. A finite element method modeling was performed to estimate the inter-strand resistivities required to enable different levels of current sharing. The relative contributions of coupling and hysteretic magnetization (and loss) were compared, and for our cable and tape geometry, and at dB/dt = 1 T s−1, and our inter-strand resistance of 0.77 mΩ, (enabling a current sharing of 5% at 1.3I c ) the coupling component was 0.32% of the hysteretic component. However, inter-strand contact resistance values of 100–1000 times smaller (close to those of NbTi and Nb3Sn based accelerator cables) would make the coupling components comparable in size to the hysteretic components.
    No preview · Article · May 2015 · Superconductor Science and Technology

  • No preview · Article · Jan 2015 · IEEE Transactions on Applied Superconductivity
  • M Majoros · M D Sumption · E W Collings · D C van der Laan
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    ABSTRACT: Described are the results of magnetization loss measurements made at 77 K on several YBCO conductor-on-round-core (CORC) cables in ac magnetic fields of up to 80 mT in amplitude and frequencies of 50 to 200 Hz, applied perpendicular to the cable axis. The cables contained up to 40 tapes that were wound in as many as 13 layers. Measurements on the cables with different configurations were made as functions of applied ac field amplitude and frequency to determine the effects of their layout on ac loss. In large scale devices such as e.g. Superconducting Magnetic Energy Storage (SMES) magnets, the observed ac losses represent less than 0.1% of their stored energy.
    No preview · Article · Dec 2014 · Superconductor Science and Technology
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    Full-text · Dataset · Sep 2014
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    ABSTRACT: A series of MgB2 superconducting composite strands co-doped with Dy2O3 and C were prepared via an advanced internal Mg infiltration (AIMI) route. The transport properties and MgB2 layer growth were studied in terms of the Dy2O3 doping level, reaction temperature, and reaction time. Transport studies showed that both critical current densities, Jcs, and irreversibility fields, Birrs, were increased with Dy2O3 doping. The highest layer Jc was 1.35 × 10^5 A/cm2 at 4.2 K, 10 T, 30 % higher than that of the best AIMI wires without Dy2O3 doping. The highest “non-barrier” Jc reached 3.6 × 10^4 A/cm2 at 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 Jc reached 10^4 A/cm2 was 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 Birr was seen at 10 K and 15 K, the increases in Jc at higher temperatures were consistent with observed increases in Birr of 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 MgB2 was enhanced by Dy2O3 doping.
    Full-text · Article · Sep 2014 · Applied Physics Letters
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    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.
    Full-text · Article · Aug 2014 · Superconductor Science and Technology
  • 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.
    No preview · Article · Jun 2014 · Superconductor Science and Technology
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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.
    No preview · Article · Jun 2014 · IEEE Transactions on Applied Superconductivity
  • E.W. Collings · M.A. Susner · M.D. Sumption · D.R. Dietderich
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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.
    No preview · Article · Jun 2014 · IEEE Transactions on Applied Superconductivity
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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.
    Full-text · Article · Jun 2014 · IEEE Transactions on Applied Superconductivity
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    Xingchen Xu · Edward Collings · Michael Sumption · Chris Kovacs · Xuan Peng
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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) .
    Full-text · Article · Jun 2014 · IEEE Transactions on Applied Superconductivity

Publication Stats

3k Citations
382.56 Total Impact Points

Institutions

  • 1992-2015
    • The Ohio State University
      • Department of Materials Science and Engineering
      Columbus, Ohio, United States
  • 2005
    • Kagoshima University
      Kagosima, Kagoshima, Japan
  • 2001
    • Lawrence Berkeley National Laboratory
      • Nuclear Science Division
      Berkeley, California, United States
  • 1999
    • Yamaguchi University
      • Department of Electrical and Electronic Engineering
      Yamaguti, Yamaguchi, Japan
  • 1995
    • University of Wollongong
      • Institute for Superconducting and Electronic Materials
      City of Greater Wollongong, New South Wales, Australia
  • 1968-1995
    • Battelle Memorial Institute
      • Department of Physics
      Columbus, Ohio, United States
  • 1991
    • Iowa State University
      Ames, Iowa, United States
  • 1975
    • Wichita State University
      Wichita, Kansas, United States