319 results on '"M.D. Sumption"'
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2. The Roles of Grain Boundary Refinement and Nano-Precipitates in Flux Pinning of APC Nb3Sn
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M.D. Sumption, Xingchen Xu, J Rochester, X Peng, and Mattia Ortino
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Flux pinning ,Materials science ,Condensed matter physics ,Diffusion ,Alloy ,Oxide ,engineering.material ,Condensed Matter Physics ,01 natural sciences ,Grain size ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,engineering ,Grain boundary ,Electrical and Electronic Engineering ,010306 general physics ,Pinning force ,Solid solution - Abstract
Internally oxidized Nb3Sn wires with artificial pinning centers (APC) have been developed by manufacturing a multifilament PIT-style wire, each filament consisting of a Nb-Ta-Zr alloy tube filled with a mixture of Sn, Cu, and oxide powders. During heat treatment, the oxide decomposes, and the oxygen goes into solid solution in the Nb alloy. Upon Sn diffusion into the Nb alloy, ZrO2 nanoprecipitates form which serve both to inhibit grain coarsening and directly pin magnetic flux. The finer grain structure and high concentration of non-superconducting precipitates serve as flux pinning sites and enhance high-field J c; direct pinning by the precipitates also shifts the maximum pinning force to higher fields. To distinguish these two effects, an APC wire with a high heat treatment temperature (700 °C) was compared to a conventional PIT wire with very low heat treatment temperature (600 °C), resulting in similar grain size in both samples. The pinning force vs applied field ( F p -B ) curve was deconvoluted into grain boundary and point pinning components. It was found that the grain boundary component of the APC wire was very close to the F p- B curve for the PIT wire, demonstrating that the two pinning components in an APC wire are directly additive. It was then possible to show that, in the 15-20 T regime, direct pinning contributed 45-50% of the total pinning.
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- 2021
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3. YBCO Coated Conductor Interlayer Electrical Contact Resistance Measured From 77 K to 4 K Under Applied Pressures up to 9.4 MPa
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E.W. Collings, M.D. Sumption, and S.C. Xue
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Materials science ,Contact resistance ,Condensed Matter Physics ,01 natural sciences ,Temperature measurement ,Electrical contacts ,Electronic, Optical and Magnetic Materials ,Conductor ,Transverse plane ,Stack (abstract data type) ,0103 physical sciences ,Electrical and Electronic Engineering ,Composite material ,010306 general physics ,Contact area ,Electrical conductor - Abstract
The inter-tape resistance is a key parameter for REBCO coated conductors, cables, and coils for various applications. We explored the transverse resistance for sets of REBCO tape stacks, measured in a “through-the-stack” configuration. For the first measurements (Rig 1), the stacks were cooled to LN2 temperature and the tape stack resistance was measured as a function of applied pressure (i.e., the pressure was applied during the measurement) up to 417 kPa. We analyzed these direct measurements to examine the contributions of the tape surfaces vs the internal tape contributions, and the results were translated into a contact efficiency, η , defined as η = Rc*Ac (the contact resistance * contact area). It was found that the electrical contact efficiency, η , for an un-pressurized stack was ≅ 0.934 Ω•cm2, but was reduced by a factor of 8 under 417 kPa of pressure to η ≅ 0.111 Ω•cm2. A second test rig was used to explore tape stack resistances from 4.2 K – 77 K. This rig allowed pressures of up to 9.94 MPa to be applied. Here, the pressure was first applied, and then the sample was cooled. This difference between Rig 1 and Rig 2 allowed us to compare the protocols of fixed pressure (Rig 1) and fixed constraint (Rig 2). The contact efficiency reached 178 μΩ•cm2 at 4.2 K and 232 μΩ•cm2 at 77 K.
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- 2021
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4. The Magnetization of Bi:2212 Rutherford Cables for Particle Accelerator Applications
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C. S. Myers, Tengming Shen, J Rochester, M.D. Sumption, E.W. Collings, and Milan Majoros
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Rutherford cable ,Materials science ,High-temperature superconductivity ,Condensed matter physics ,Magnetometer ,Particle accelerator ,Superconducting magnet ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetization ,law ,Magnet ,0103 physical sciences ,Electromagnetic shielding ,Electrical and Electronic Engineering ,010306 general physics - Abstract
High temperature superconductors, including Bi:2212, are being considered for high magnetic field magnets to be used in particle accelerators. A knowledge of HTS magnetization properties are needed for calculating field errors in such accelerator magnets. Here we present magnetic measurements of a 17 strand Bi:2212 Rutherford cable. The Bi:2212 strand was a Bruker OST PMM170123 non-twisted wire wound into a cable with dimensions 1.46 mm x 7.8 mm and cable pitch of 50.8 mm. M-H loop measurements were made with a Hall probe at 4.2 K. Two calibration methods were compared, (i) a flux exclusion approach, and (ii) a Ni replacement technique. The latter was found to be more reliable in this case. An effective filament diameter of 358 μm was calculated for the strand at 4.2 K and a perpendicular applied field of 3.33 T, significantly larger than the diameter of the filament bundle. Magnetization values at 1 T on the shielding branch were seen to be 100 kA/m when normalized to the total strand in the cable volume. The penetration field ≅ 0.4 T.
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- 2021
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5. Electrical and mechanical properties of high electrical conductivity CNT/Cu‐yarns with Br doping and Cu encapsulation
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C J Thong, Yu Mao, Michael Tomsic, M.D. Sumption, E.W. Collings, Shengchen Xue, C. Kovacs, and John Philips
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high specific strength ,Materials science ,Doping ,Carbon nanotube ,high specific conductivity ,Encapsulation (networking) ,law.invention ,Chemical engineering ,Electrical resistivity and conductivity ,law ,TA401-492 ,dopants stabilization ,carbon nanotube ,composite conductor ,Materials of engineering and construction. Mechanics of materials - Abstract
Carbon nanotubes (CNTs) are an ideal starting material for the development of strong, light‐weight conductors. In this work, we pursued the development of high specific electrical conductivity and high specific strength CNT/metal composites. We started with CNT yarns which had an initial electrical conductivity, σe, of 3.14 MS m‐1 and a density of 1.32 g cm‐3. We brominated the yarns, demonstrating increases in σe, with our best samples reaching σe = 7.00 MS m‐1. To increase the stability of the bromination, we electroplated a Cu layer onto the Br‐doped yarn which led to a stabilization of the conductivity improvement. This was quantified by monitoring periodically the σe of a Br‐doped and metallized CNT yarn over a period of 69 days, during which time the sample was otherwise exposed to ambient conditions. Analysis gives a value 6.15 MS m‐1 for the brominated yarn after metallization which is excellent for CNT yarns. Tensile tests on these Cu/CNT composites showed tensile strengths reaching 700 MPa, Young's modulus values of 22.8 GPa, and specific tensile strength values of 146 kN*m kg‐1 (this latter is 6X that of Cu). Our best CNT‐Cu composites show specific conductivity values comparable with that of Cu but with much higher specific tensile strengths.
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- 2021
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6. High critical current density in internally-oxidized Nb3Sn superconductors and its origin
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X Peng, J Rochester, M.D. Sumption, Jaeyel Lee, and Xingchen Xu
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010302 applied physics ,Superconductivity ,Materials science ,Condensed matter physics ,Mechanical Engineering ,education ,Metals and Alloys ,02 engineering and technology ,Atom probe ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Future Circular Collider ,Grain size ,law.invention ,Mechanics of Materials ,Transmission electron microscopy ,law ,0103 physical sciences ,General Materials Science ,Critical current ,0210 nano-technology - Abstract
We report achievement of non-Cu-matrix critical current density (Jc) in internally-oxidized Nb3Sn superconductors that surpasses the best state-of-the-art Nb3Sn and the Jc specification of the Future Circular Collider. We then explore the mechanism of the improvement, which was believed to be caused by refined grain size. However, our experiment showed that even with similar grain size, internally-oxidized wires had significantly higher Jc than non-oxidized wires. This, combined with transmission electron microscopy and atom probe tomography studies which showed a high density of intragranular nano-precipitates with suitable sizes as pinning centers in internally-oxidized wires, demonstrates a significant contribution from the nano-precipitates.
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- 2020
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7. Modified Interconductor Contact Resistivity in Coated Conductor Stacks and Roebel Cables
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M.D. Sumption, E.W. Collings, C. Kovacs, and Milan Majoros
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Materials science ,Contact resistance ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Conductor ,Stack (abstract data type) ,Electrical resistivity and conductivity ,0103 physical sciences ,Surface roughness ,Electrical and Electronic Engineering ,Composite material ,010306 general physics ,Layer (electronics) ,Electrical conductor ,Diffusion bonding - Abstract
Interconductor contact resistivity ( ICR ) is a key property in determining the stability and current sharing of coated conductor cables. Most coated conductor cables have relatively high contact resistivity and low current sharing as fabricated because of surface roughness and an oxide layer that forms on the Cu-stabilizer. Here we work to quantify the differences in using three methods to modify ICR : sample diffusion bonding, deposition surface modification, and thin conformable inserts. At first a stack of two coated conductors was used to simulate a cable. This stack was put under transverse pressure and exposed to moderate temperatures to promote diffusion bonding via the removal of the unstable Cu-oxide layer ( ICR measurements were performed on stacks before and after diffusion bonding, for stacks with deposited surface layers, and for stacks with a smart material insert. In addition, Roebel cables were prepared with deposited layers on the individual strands and atmospherically controlled diffusion bonding, and ICR was compared between the as-received and modified Roebel cables as well as coated conductor stacks.
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- 2020
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8. Study the Impact of Magnetic Field on Dosimetry of Proton Therapy Using Monte Carlo Simulation
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A. Ben Ali, M. Majoros, X. Zhang, E.W. Collings, N. Gupta, M.D. Sumption, and L. Lu
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Cancer Research ,Radiation ,Oncology ,Radiology, Nuclear Medicine and imaging - Published
- 2022
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9. Magnetization Measurements of CORCTMand Roebel Type YBCO Cables for Accelerators Using a ±3-T Dipole Magnetometer
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E.W. Collings, Milan Majoros, M.D. Sumption, and C. Kovacs
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Materials science ,business.industry ,Magnetometer ,Superconducting magnet ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetization ,Dipole ,Optics ,law ,Magnet ,0103 physical sciences ,Pickup ,Electrical and Electronic Engineering ,010306 general physics ,business ,Magnetic dipole ,Electrical conductor - Abstract
We present measurements on high-temperature superconducting (HTS) superconducting cables using a NbTi-wound, 3-T dipole ac magnetometer. Our goal is to measure the magnetization properties of the cables for use in accelerator magnet field error calculations. YBCO-wound CORCTM and Roebel cables were measured in pool boiling helium with no epoxy impregnation. The Roebel cable was a 9–5.6 style, while the CORCTM sample had 16 tapes, and was 3.21 mm OD. For measurement, the samples were inserted in a G-10 holder with pickup and compensation coils, and subjected to a ramping dipole field. The signals were read from a set of nanovoltmeters using data aquisition (DAQ) to monitor the pickup coils, and the data were imported into a LabVIEW software program. The Roebel and CORCTM cable measurements were compared to one another and to the tapes they were made with. Maximum cable magnetization was 1000 kA/m for the CORC and 2200 kA/m for the Roebel when normalizing to total cable volume. These values increased to 2860 and 2640 kA/m, respectively, when normalizing to tape volume.
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- 2019
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10. Study of Superconducting, Structural, and Thermal Properties of SnO2 Added MgB2 Bulks
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Danlu Zhang, Chee J. Thong, E.W. Collings, M A Rindfleisch, and M.D. Sumption
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Diffraction ,Superconductivity ,Materials science ,Doping ,Analytical chemistry ,chemistry.chemical_element ,Condensed Matter Physics ,01 natural sciences ,Oxygen ,Article ,Electronic, Optical and Magnetic Materials ,Physical property ,chemistry ,Lattice (order) ,0103 physical sciences ,Electrical and Electronic Engineering ,010306 general physics ,Thermal analysis ,Critical field - Abstract
A series of SnO 2 added MgB 2 bulk superconductors were prepared by in situ route to study the effect of oxygen doping on superconducting and structural properties of MgB 2 . Several (MgB 2 ) 1-x (SnO 2 ) x samples were fabricated with x ranging from 0, 3 wt%, 4 wt%, and 6 wt%. Upper critical field (B c2 ) and irreversible field (B irr ) were measured by physical property measurement system. Thermal analysis was performed on the as-received SnO 2 powder. Critical current densities (J cm ) were obtained at 4.2 K using magnetic measurement. X-ray diffraction results showed evidence of full SnO 2 decomposition in all the doped bulk samples and a shift of a-axis in MgB 2 lattice was seen. Oxygen was successfully released during heat treatment, yet no enhancement of B C2 or B irr was seen, indicating that oxygen atoms did not end up in the host lattice. Further exploration of different processing procedures is still needed in order to get oxygen substitution on the host lattice sites.
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- 2019
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11. A Tear-Drop Bifilar Sample Holder for Full Excitation and Stability Studies of HTS Cables at 4.2 K Using a Superconducting Transformer
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Milan Majoros, C. Kovacs, Alexander V. Zlobin, Emanuela Barzi, and M.D. Sumption
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Superconductivity ,Materials science ,System of measurement ,Bifilar coil ,Mechanical engineering ,Solenoid ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,Transverse plane ,law ,Magnet ,Electrical and Electronic Engineering ,Transformer ,Excitation - Abstract
HTS cables proposed for next-generation main, hybrid, and insert magnets will have very high I c (>10 kA) at 14 T and above. Determining the quench, current-sharing, and other properties of these cables will require measurement systems, which will likely incorporate a superconducting transformer. The utilization of high-field persistent mode solenoids will make size and cost less prohibitive, allowing a higher frequency of measurements within a larger number of research facilities. Additionally, a system designed for use with solenoids will allow for experiments at higher maximum fields than those achievable using dipoles and split coils. Proposed in this document is a bifilar sample probe, which fits within a 77-mm bore solenoid capable of measuring up to a 6-mm outer diameter conductor-on-round-core REBCO cables or wires up to 20 kA in transverse fields at 12 T and 4.2 K. Splices and mechanical considerations will be discussed.
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- 2019
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12. Quench Measurements in a YBCO Pancake Coil at 77 K and 4.2 K in Magnetic Fields up to 10 Tesla
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Milan Majoros, Danlu Zhang, M.D. Sumption, and E.W. Collings
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Materials science ,Condensed matter physics ,Liquid helium ,Voltage limit ,Liquid nitrogen ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetic field ,law ,Electromagnetic coil ,Thermocouple ,Electrical and Electronic Engineering ,Current (fluid) ,Voltage - Abstract
We measured stability and quench in a YBCO pancake coil in liquid nitrogen bath (77.3 K) and in liquid helium bath (4.2 K) with externally applied magnetic fields up to 10 T. The pancake coil was instrumented with voltage taps and thermocouples in the winding for measurements of radial and azimuthal quench propagations. A heater was placed on the inner-most part of the winding. Heat pulses of various powers and durations were generated at different coil currents to measure quench and normal zone propagation. A protection circuit with a possibility of setting different quench voltage limits was used to turn off the coil current after the voltage limit was exceeded.
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- 2019
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13. Magnetization and Flux Penetration of YBCO CORC Cable Segments at the Injection Fields of Accelerator Magnets
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C. S. Myers, M.D. Sumption, and E.W. Collings
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Superconductivity ,Materials science ,Condensed matter physics ,Magnetometer ,Beam steering ,Particle accelerator ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetic field ,Magnetization ,law ,Condensed Matter::Superconductivity ,Magnet ,0103 physical sciences ,Physics::Accelerator Physics ,Electrical and Electronic Engineering ,010306 general physics ,Electrical conductor - Abstract
High-temperature-superconducting (HTS) cables are being considered for use in particle accelerator beam steering magnets. Knowledge of the magnetic properties of these HTS cables is needed for accelerator magnet design. Here, we present the results from a Hall probe magnetometer made for measuring the M-μ 0 H of short sections of superconducting cables in applied magnetic fields up to 12 T. The M-μ 0 H of a CORC cable was measured with field sweeps of ± 4.5 T and also a -2- to 8-T loop. Relevant to a particle accelerator with an injection field of 1 T, the magnetization M inj of the CORC cable was ≅ 900 kA/m and the penetration field B p ≅ 1 T. The magnetization and penetration field of the cables are compared to tape from which the cables were wound, and the results are compared to NbTi and Nb 3 Sn conductors.
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- 2019
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14. Magnetization and Creep in YBCO Tape and CORC Cables for Particle Accelerators: Value and Modification Via Preinjection Cycle
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E.W. Collings, M.D. Sumption, and C. S. Myers
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Superconductivity ,Materials science ,Condensed matter physics ,Magnetometer ,Persistent current ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Magnetic field ,law.invention ,Magnetization ,Dipole ,law ,Condensed Matter::Superconductivity ,Magnet ,0103 physical sciences ,Electrical and Electronic Engineering ,010306 general physics ,Quadrupole magnet - Abstract
High-temperature superconductors (HTSs), including YBCO coated conductors, are being considered for high field dipole and quadrupole magnets for future particle accelerators. The quality of the magnetic field generated by the magnet and its temporal stability are important considerations. The persistent current magnetization of superconductors can degrade the field quality of the magnetic field generated by magnets made from them by causing error fields, and flux creep in the superconductor may lead to drift in the value of the magnetic field during magnetic field ramp holding sequences, including at particle injection. HTS composites possess larger persistent current magnetizations and larger flux creep than low-temperature superconductor composites, and therefore, the error fields and any temporal change of them are typically larger. In this paper, the 4.2 K magnetization of a small segment of coated conductor was measured in a vibrating sample magnetometer in perpendicular fields up to 14 T, and the decay was measured at 1 T. The magnetization and decay of a CORC cable were measured in a 12 T cryogen-free magnet. A Hall sensor, placed close to the sample, was used to measure the magnetization. The applied magnetic field was ramped through full flux penetration, and then, brought within one flux penetration depth of the target applied magnetic field before the decay measurement was started. Selective cycling of the magnetic field applied to the samples was explored as a technique to reduce the magnetization and its decay. Significant suppression of both the initial magnetization at 1 T and its decay were observed.
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- 2019
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15. Multi-Domain Modeling for High Temperature Superconducting Components for the CHEETA Hybrid Propulsion Power System
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Luigi Vanfretti, M.D. Sumption, Abhijit Khare, Meaghan Podlaski, and Phillip J. Ansell
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Electric power system ,Multi domain ,Materials science ,business.industry ,High temperature superconducting ,Aerospace engineering ,business ,Hybrid propulsion - Published
- 2021
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16. Design and Scaling Laws of a 40-MW-class Electric Power Distribution System for Liquid-H2 Fuel-Cell Propulsion
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Timothy J. Haugan, Mary Ann Sebastian, C. Kovacs, M.D. Sumption, and Bang-Hung Tsao
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Physics ,Electric power distribution ,Scaling law ,Class (computer programming) ,business.industry ,Fuel cells ,Propulsion ,Aerospace engineering ,business - Published
- 2021
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17. Quench, Normal Zone Propagation Velocity, and the Development of an Active Protection Scheme for a Conduction Cooled, RW, MgB
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Michael Martens, David Doll, M.J. Tomsic, M.D. Sumption, Charles Poole, E.W. Collings, C. Kovacs, D Panik, Milan Majoros, Danlu Zhang, and M A Rindfleisch
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010302 applied physics ,Superconductivity ,Work (thermodynamics) ,Materials science ,Metals and Alloys ,Mechanics ,Condensed Matter Physics ,Thermal conduction ,01 natural sciences ,Article ,Normal zone ,Electromagnetic coil ,Magnet ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Development (differential geometry) ,Electrical and Electronic Engineering ,010306 general physics ,Voltage - Abstract
The development of coils that can survive a quench is crucial for demonstrating the viability of MgB(2)-based main magnet coils used in MRI systems. Here we have studied the performance and quench properties of a large (outer diameter: 901 mm; winding pack: 44 mm thick × 50.6 mm high) conduction-cooled, react-and-wind (R&W), MgB(2) superconducting coil. Minimum quench energy (MQE) values were measured at several coil operating currents (I(op)), and distinguished from the minimum energy needed to generate a normal zone (MGE). During these measurements, normal zone propagation velocities (NZPV) were also determined using multiple voltage taps placed around the heater zone. The conduction cooled coil obtained a critical current (I(c)) of 186 A at 15 K. As the operating currents (I(op)) varied from 80 A to 175 A, MQE ranged from 152 J to 10 J, and NZPV increased from 1.3 to 5.5 cm/s. Two kinds of heater were involved in this study: (1) a localized heater (“test heater”) used to initiate the quench, and (2) a larger “protection heater” used to protect the coil by distributing the normal zone after a quench was detected. The protection heater was placed on the outside surface of the coil winding. The test heater was also placed on the outside surface of the coil at a small opening made in the protection heater. As part of this work, we also developed and tested an active protection scheme for the coil. Such active protection schemes are of great interest for MgB(2)-based MRIs because they permit exploitation of the relatively large MQE values of MgB(2) to enable the use of higher J(e) values which in turn lead to competitive MgB(2) MRI designs. Finally, the ability to use a quench detection voltage to fire a protection heater as part of an active protection scheme was also demonstrated.
- Published
- 2021
18. Potential Applications of MTS and HTS to MRI Imaging Systems for Particle Beam Therapy
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M.D. Sumption, E.W. Collings, L. Lu, N. Gupta, and Milan Majoros
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Cancer Research ,Radiation ,Particle therapy ,business.industry ,medicine.medical_treatment ,Bragg peak ,Transverse plane ,Optics ,Oncology ,Deflection (engineering) ,Magnet ,Medicine ,Radiology, Nuclear Medicine and imaging ,Particle beam ,business ,Charged particle beam ,Beam (structure) - Abstract
Purpose/Objective(s) To explore the potential application of medium temperature superconductors (MTS) and high temperature superconductors (HTS) to the development of background magnets for MRI systems for use in combination with particle beam therapy (PBT) and the concept design for MRI-guided PBT. Materials/Methods In proton/heavy ion therapy, because of the sharp dose drop off owing to the Bragg peak effect, imaging guidance becomes crucial. Various imaging techniques have been considered, but MRI, with its soft tissue contrast, 3D imaging, high spatial resolution, and potential on-live monitoring feature would be particularly useful in combination with PBT. One of the key challenges is that the charged particle beam will be deflected in a transverse magnetic field. The deflection of the particle beam in the presence of the background B0 has received significant interest, and both in-line and transverse configurations have been considered. For in-line configurations, smaller deflections are seen, with some rotation, and for transverse, greater deflection, and momentum change. With the use of a pencil beam PCT approach in combination with computation, such deflections can in principle be compensated. However, if “real time” imaging is to be enabled, minimum computation and reconstruction time is desirable. For these reasons, minimizing and simplifying the deflection is desirable. This can be enabled with the use of the in-line configuration, but in this case an in-line system compacts enough to mount on a gantry may be of interest. This can be made more achievable with the use of MTS or HTS where less bulky magnets are possible, cooling is simplified, and systems are much less quench sensitive. At the same time, the minimization of fringe fields can also substantially simplify the particle beam trajectories and minimize their deflection. This may also be enabled for open configuration transverse configurations with the use of less bulky HTS and MTS magnets. For this work we performed magnetic modelling of several different configurations of MTS and HTS magnets, both in-line and transverse, using Vector fields and other modelling software. The sizes and configurations of the MTS and HTS systems as compared to potential competing LTS systems were then compared. Particle beam trajectories were then computed with GEANT software and compared. Results (1) MTS and HTS systems can allow the development of in-line MR which are sufficiently compact, open, and robust (to quench) to allow mounting on a gantry. This reduces particle beam deflection, while at the same time allowing rotation of the beam around the patient; (2) Several designs for minimized fringe fields are given, both for in-line and transverse configurations. Conclusion MTS and HTS have a significant potential for application to MRI-guided Particle Therapy based on their potential for mounting on a gantry, and enabling of more open background magnet configurations. Magnet designs with minimized fringe fields are also possible and useful.
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- 2021
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19. Enhanced higher temperature irreversibility field and critical current density in MgB(2) wires with Dy(2)O(3) additions
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M.J. Tomsic, E.W. Collings, M.D. Sumption, Y. Yang, and M A Rindfleisch
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Materials science ,Flux pinning ,Doping ,Metals and Alloys ,Analytical chemistry ,Condensed Matter Physics ,Crystallographic defect ,Article ,chemistry.chemical_compound ,chemistry ,Transmission electron microscopy ,Materials Chemistry ,Ceramics and Composites ,Magnesium diboride ,Grain boundary ,Electrical and Electronic Engineering ,Critical field ,Pinning force - Abstract
Bulk samples of magnesium diboride (MgB2) doped with 0.5 wt% of the rare earth oxides (REOs) Nd2O3 and Dy2O3 (named B-ND and B-DY) prepared by standard powder processing, and wires of MgB2 doped with 0.5 wt% Dy2O3 (named W-DY) prepared by a commercial powder-in-tube processing were studied. Investigations included x-ray diffractometry, scanning- and transmission electron microscopy, magnetic measurement of superconducting transition temperature (T c), magnetic and resistive measurements of upper critical field (B c2) and irreversibility field (B irr), as well as magnetic and transport measurements of critical current densities versus applied field (J cm(B) and J c(B), respectively). It was found that although the products of REO doping did not substitute into the MgB2 lattice, REO-based inclusions resided within grains and at grain boundaries. Curves of bulk pinning force density (F p) versus reduced field (b = B/B irr) showed that flux pinning was by predominantly by grain boundaries, not point defects. At all temperatures the F p(b) of W-DY experienced enhancement by inclusion-induced grain boundary refinement but at higher temperatures F p(b) was still further increased by a Dy2O3 additive-induced increase in B irr of about 1 T at all temperatures up to 20 K (and beyond). It is noted that Dy2O3 increases B irr and that it does so, not just at 4 K, but in the higher temperature regime. This important property, shared by a number of REOs and other oxides promises to extend the applications range of MgB2 conductors.
- Published
- 2021
20. Quench and stability of Roebel cables at 77 K and self-field: Minimum quench power, cold end cooling, and cable cooling efficiency
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Milan Majoros, C. Kovacs, E.W. Collings, and M.D. Sumption
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010302 applied physics ,Materials science ,General Physics and Astronomy ,Stability diagram ,Mechanics ,01 natural sciences ,Leidenfrost effect ,Heat generation ,0103 physical sciences ,General Materials Science ,Critical current ,010306 general physics ,Self field ,Cooling efficiency - Abstract
A 9-tape, 14 mm wide ReBCO Roebel cable was soldered onto a U-shaped holder. The critical current, Ic, was measured at 77 K and self-field. The cryostability of the cable was studied in response to the application of local pulses of 1–14 W at several values of i = I/Ic. A detailed analysis of the cable’s cryostability was presented. With a Stekly parameter α = G/Q « 1 and a heat generation margin of ∼190 kW/m2 the present ReBCO cable was shown to be ultra cryostable with respect to internally generated transport-current overload. However, the cable was much less stable against externally and locally applied disturbances because of the tendency to initiate local film boiling. A locally applied 10 W led to a prediction of a film-boiling-cooled zone with a temperature of 181 K. However, when cold-end cooling was considered, the predicted hot spot temperature decreased to 87–115 K depending on the surface-cooling efficiency. Predictions were compared to experiment extracting a cooling efficiency parameter representing the penetration of the cryogen into the cable. Experiment showed the generation of time stable normal zones which were a function of disturbance power. This led to the description of the cable stability in terms of minimum quench power; the results are presented in stability diagrams.
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- 2018
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21. Effect of biaxial cold pressure densification (BCPD) on Ba0.6K0.4Fe2As2 round wire using optimized precursor
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Zhixiang Shi, Mike Tomsic, S.C. Xue, E.W. Collings, F Wan, M A Rindfleisch, Xiaodong Li, M.D. Sumption, and Dan Zhang
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Superconductivity ,Materials science ,Annealing (metallurgy) ,Process Chemistry and Technology ,Metallurgy ,Sintering ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Critical current ,010306 general physics ,0210 nano-technology - Abstract
(Ba,Sr) 1- x K x Fe 2 As 2 superconductor is of great interest as a wire for practical applications. In this paper, Ba 0.6 K 0.4 Fe 2 As 2 precursor powder was prepared by high-energy ball-milling aided sintering (12 h/750 °C). The prepared precursor was drawn to powder-in-tube round wire. Partial as-drawn wires were subjected to biaxial cold pressure densification (BCPD) at 0.5 and 1.0 GPa, followed by an annealing for 1 min/770 °C. According to our results, the BCPD improved the grain connectivity of the BCPDed wires without degrading the superconductivity. A (Ba,Sr) 1- x K x Fe 2 As 2 round-wire record transport critical current density, 1.14×10 5 A/cm 2 (4.2 K, 2 T), was observed in our BCPDed samples.
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- 2018
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22. AC losses of Roebel and CORC® cables at higher AC magnetic fields and ramp rates
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John Murphy, Milan Majoros, Danko van der Laan, Timothy J. Haugan, Nicholas J. Long, E.W. Collings, and M.D. Sumption
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Materials science ,CORC ,Nuclear engineering ,Materials Chemistry ,Metals and Alloys ,Ceramics and Composites ,Electrical and Electronic Engineering ,Condensed Matter Physics ,computer ,computer.programming_language ,Magnetic field - Abstract
We have measured ReBCO coated conductor-based conductor on round core (CORC®) and Roebel cables at 77 K in a spinning magnet calorimeter, which subjected the tapes in the samples to a radial magnetic field of 566 mT (peak) at frequencies up to 120 Hz (272 T s−1, cyclic average) with an approximately sinusoidal waveform. The samples were oriented such that the field applied to the tapes within the cables was entirely radial, simplifying subsequent analysis. An expression for loss which included hysteretic, flux creep and eddy current losses was fit to both the CORC® and the Roebel cables. This expression allowed easy comparison of the relative influence of eddy currents and flux creep (or power-law behavior) effects. The loss of both the CORC ® and Roebel cables measured here were seen to be essentially the sum of the hysteretic loss, flux creep effects, and the normal metal eddy current losses of the individual tapes. The losses of these cables were measured at high B × dB/dt with no coupling current loss observed under the present preparation conditions. The influence of flux creep effects on loss were not negligible. The losses of the CORC® cable per meter of tape were seen to be reduced from the case of a flat tape because of the helical geometry of the tapes.
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- 2021
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23. AC loss in YBCO coated conductors at high dB/dt measured using a spinning magnet calorimeter (stator testbed environment)
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M.D. Sumption, T.J. Haugan, N.N. Gheorghiu, Milan Majoros, T. J. Bullard, John P. Murphy, and E.W. Collings
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010302 applied physics ,Materials science ,Solenoidal vector field ,business.industry ,Stator ,General Physics and Astronomy ,01 natural sciences ,Calorimeter ,law.invention ,Halbach array ,Optics ,Amplitude ,Nuclear magnetic resonance ,law ,Magnet ,0103 physical sciences ,Eddy current ,General Materials Science ,010306 general physics ,business ,Residual-resistance ratio - Abstract
A new facility for the measurement of AC loss in superconductors at high dB/dt has been developed. The test device has a spinning rotor consisting of permanent magnets arranged in a Halbach array; the sample, positioned outside of this, is exposed to a time varying AC field with a peak radial field of 0.566 T. At a rotor speed of 3600 RPM the frequency of the AC field is 240 Hz, the radial dB/dt is 543 T/s and the tangential dB/dt is 249 T/s. Loss is measured using nitrogen boiloff from a double wall calorimeter feeding a gas flow meter. The system is calibrated using power from a known resistor. YBCO tape losses were measured in the new device and compared to the results from a solenoidal magnet AC loss system measurement of the same samples (in this latter case measurements were limited to a field of amplitude 0.1 T and a dB/dt of 100 T/s). Solenoidal magnet system AC loss measurements taken on a YBCO sample agreed with the Brandt loss expression associated with a 0–0.1 T Ic of 128 A. Subsequently, losses for two more YBCO tapes nominally identical to the first were individually measured in this spinning magnet calorimeter (SMC) machine with a Bmax of 0.566 T and dB/dt of up to 272 T/s. The losses, compared to a simplified version of the Brandt expression, were consistent with the average Ic expected for the tape in the 0–0.5 T range at 77 K. The eddy current contribution was consistent with a 77 K residual resistance ratio, RR, of 4.0. The SMC results for these samples agreed to within 5%. Good agreement was also obtained between the results of the SMC AC loss measurement and the solenoidal magnet AC loss measurement on the same samples.
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- 2017
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24. Recent Progress in Application of Internal Oxidation Technique in Nb3Sn Strands
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X Peng, M.D. Sumption, Xingchen Xu, and E.W. Collings
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Materials science ,Dopant ,Doping ,Nanoparticle ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Grain size ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,chemistry ,0103 physical sciences ,Electrical and Electronic Engineering ,Niobium-tin ,010306 general physics ,0210 nano-technology ,Internal oxidation ,Current density ,Titanium - Abstract
The internal oxidation technique can generate ZrO 2 nano particles in Nb 3 Sn strands, which markedly refine the Nb 3 Sn grain size and boost the high-field critical current density (J c ). This paper summarizes recent efforts on implementing this technique in practical Nb 3 Sn wires and adding Ti as a dopant. It is demonstrated that this technique can be readily incorporated into the present Nb 3 Sn conductor manufacturing technology. Powderin-tube (PIT) strands with fine subelements (~25 μm) based on this technique were successfully fabricated, and proper heat treatments for oxygen transfer were explored. Future work for producing strands ready for applications is proposed.
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- 2017
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25. Demonstration of a Practical Nb$_3$ Sn Coil for an Actively Shielded Generator
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X Peng, J. Yue, E. W. Collings, David Loder, Milan Majoros, David Doll, M.D. Sumption, Reed Sanchez, Kiruba S. Haran, Chris Kovacs, and Matthew Feddersen
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010302 applied physics ,Electric machine ,Materials science ,business.product_category ,Superconducting electric machine ,Mechanical engineering ,Superconducting magnetic energy storage ,Superconducting magnet ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,law.invention ,Generator (circuit theory) ,Nuclear magnetic resonance ,Electromagnetic coil ,law ,0103 physical sciences ,Electromagnetic shielding ,Shielded cable ,Electrical and Electronic Engineering ,010306 general physics ,business - Abstract
This paper describes a detailed design of a 6-T Nb 3 Sn superconducting racetrack coil designed for conduction cooling. We then describe a bench test pursued as a proof of concept for one winding of an actively shielded air-core electric machine with superconducting field windings. Electromagnetic design selection is drawn from previous optimization work. The coil former design is then discussed. Numerical simulations of thermal and structural features are pursued to determine temperature distribution and strain within the winding. A coil instrumentation and experimental setup of a quasi-conduction cooled system is described. Finally, test results are presented; a maximum critical current of 480 A was reached at a peak temperature of 7.9 K, surpassing the operational current goal of 435 A. Future work and planned improvements to the test setup are discussed.
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- 2017
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26. Fabrication and Superconductivity of Ba0.6K0.4Fe2As2/Ag Wires and Tapes Using Mechanical Alloyed Precursor
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Zhi Xiang Shi, C. S. Myers, Xiong Li, M.D. Sumption, F Wan, and E.W. Collings
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Superconductivity ,Materials science ,Fabrication ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,0103 physical sciences ,Critical current ,Electrical and Electronic Engineering ,Composite material ,010306 general physics ,0210 nano-technology ,Ball mill ,Groove (engineering) - Abstract
Conventional methods of Ba 0.6 K 0.4 Fe 2 As 2 precursor preparation are complicated and expensive. In this paper, we describe the mechanical alloying of precursor by high-energy ball milling and its processing to wires and tapes. Our approach is to high-energy ball-mill a starting mixture of Ba and K pieces with Fe and As powders. The resultant powders are packed into an Ag sheath and reduced by groove rolling or flat rolling. Critical current density measurements were performed on unsintered wire and tape, and compared to the results of measurements on wire and tape sintered at 750 °C for 12 h. We achieved 6.98 × 10 4 A/cm 2 at 4.2 K and self-field in the sintered tape. Our results indicate that the mechanical alloyed precursor and the resulting Ag-sheathed Ba 0.6 K 0.4 Fe 2 As 2 wires and tapes are promising but require further development.
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- 2017
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27. AC Loss Reduction in Multifilamentary Coated Conductors With Transposed Filaments
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M.D. Sumption, Xiao-Fen Li, Venkat Selvamanickam, Anis Ben Yahia, and Milan Majoros
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010302 applied physics ,Laser ablation ,Materials science ,Transposition (telecommunications) ,chemistry.chemical_element ,Condensed Matter Physics ,Laser ,01 natural sciences ,Copper ,Electronic, Optical and Magnetic Materials ,law.invention ,Magnetization ,chemistry ,law ,0103 physical sciences ,Electrical and Electronic Engineering ,Composite material ,010306 general physics ,Electroplating ,Electrical conductor ,Striation - Abstract
Filamentization has been shown to be an effective method in reducing magnetization ac loss of RE-Ba-Cu-O (REBCO) coated conductors. We have used a laser striation method followed by selective electroplating of copper to fabricate fully stabilized multifilamentary REBCO tapes with 12, 24, and 46 filaments. While expected levels of ac loss reduction has been confirmed in short segments of such multifilamentary tapes, electric coupling between the filaments of long tapes needs to be suppressed by transposition of the filaments. In this work, a technique was developed and implemented to reduce ac losses in REBCO multifilamentary coated conductors through a new design that allows us to transpose the filaments without any mechanical twisting. The process consists of patterning REBCO tapes by laser ablation followed by partial insulation and bonding. A twofold reduction of ac magnetization losses was achieved in the transposed multifilamentary REBCO tape when subject to an external perpendicular magnetic field at frequencies between 50 and 200 Hz and peak field values up to 88 mT. The filament-to-filament resistance and its effect on the coupling have also been investigated.
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- 2017
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28. Architecture and Transport Properties of Multifilamentary MgB2 Strands for MRI and Low AC Loss Applications
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M.D. Sumption, Michael Tomsic, E.W. Collings, F Wan, and M A Rindfleisch
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010302 applied physics ,Materials science ,Condensed matter physics ,Monel ,engineering.material ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Conductor ,Protein filament ,Matrix (mathematics) ,Magnet ,0103 physical sciences ,engineering ,Critical current ,Electrical and Electronic Engineering ,Composite material ,010306 general physics - Abstract
Standard in-situ type MgB2 strands manufactured by Hyper Tech Inc have 19 - 36 subelements, a monel outer sheath, and a Cu interfilamentary matrix. Typical transport Jc s of the strands are 2×105 A/cm2 with n-values of 20 - 30 at 4.2 K and 5 T. This work introduces two new MgB2 conductor designs. First, a new class of MgB2 strand is designed for magnetic resonance imaging applications. This type has a higher Cu content designed to enhance protection of a magnet wound with it, and a larger diameter to increase the critical current. Second, a new class of low AC loss MgB2 strand with high filament count and a high resistance matrix is discussed. Transport properties at 4.2 K and fields up to 10 T are reported. Optical techniques are used to study the macro- and micro-structures of these MgB2 strands.
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- 2017
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29. Single-Strand Excitation for Probing Current Sharing and Parallel Resistance in Cored Nb3Sn Rutherford Cables at 4.2 K and 10 Tesla
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M.D. Sumption, E.W. Collings, and C. Kovacs
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Materials science ,Heat pulse ,Condensed Matter Physics ,01 natural sciences ,Oxygen atmosphere ,Electronic, Optical and Magnetic Materials ,Turn off ,Current sharing ,0103 physical sciences ,Electrical and Electronic Engineering ,Composite material ,Current (fluid) ,010306 general physics ,Excitation ,Voltage ,Single strand - Abstract
A rig was fabricated to test single-strand excitation and current sharing in Nb3 Sn Rutherford Cables. Measurements were performed on 400 mm lengths of a 27-strand, cored cable. In preparation for measurement, the cable was mounted onto a U-shaped holder, reacted for 72-48-50 h at 210-400-665 °C under 20 MPa. Current was injected into a single strand of the cable, and the onset of current sharing was seen above single strand Ic. After the onset of transition, the I-V showed a flat baseline the slope of which gave the transfer resistance to the two neighboring strands. Two cable samples were measured, one of which was reacted in a dilute oxygen atmosphere. The slightly oxidized cable had a R ∥ of 280 nΩ, whereas the other sample had a R,, was 70 nΩ per lay pitch. Varying I/Ic and a heat pulse from a carbon paste heater was used to turn off successive pairs of neighboring strands, and the resulting current-distribution was measured using voltage taps. These measurements were performed as a screening for cable and cable preparation protocol for larger scale measurements.
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- 2017
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30. AC Loss of Superconducting Materials- refined loss estimates for very high density motors and generators for hybrid-electric aircraft: MgB2 wires, Coated conductor tapes and wires
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M.D. Sumption, M.J. Tomsic, F Wan, and M A Rindfleisch
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Superconductivity ,Physics ,Generator (circuit theory) ,Amplitude ,law ,Electromagnetic coil ,Eddy current ,Extrapolation ,Electrical conductor ,Computational physics ,law.invention ,Conductor - Abstract
Superconducting winding are enabling for the development of the highest power density motors and generators for aircraft use. It is presently estimated that motors with standard Cu wire windings can reach a future limit of at best 20 kW/kg. On the other hand, motors with superconducting windings are estimated to be able to produce more than double this, roughly 45 kW/kg. Superconducting windings carry very large current densities (1 kA/mm2 winding J e and more) and can generate much higher winding fields (even as high as 3–8 T in some designs), but do generate losses in the windings which must be removed at cryogenic temperatures. Here we focus on comparison of calculated and measured losses for one of the most promising superconducting materials for low loss motor and generator application, MgB 2 . MgB 2 is available in the form of wires (about 0.3-1 mm OD), and as triplet or 6 x 1 cables of these wires. Here we measure the hysteretic, coupling, and eddy current components of loss for a set of low-loss, multifilamentary MgB 2 wires which have been recently developed. It is shown that present day MgB 2 conductors are capable of 1–5 W/cm3 in the 100–200 Hz range for field amplitudes of about 0.4 T, which makes them usable for motors and generators with sufficient attention to cooling design. Specific loss values are very dependent on frequency, field amplitude, and nature of the applied field (related to motor rotational speed, number of poles, and design) as well as conductor design. However, we compare low frequency results measured at 20 K and 0–3 T to theoretical expectation, and we then make extrapolations to frequencies up to 200 Hz (and give explicit expressions for such extrapolation). We in particular include here also the effect of maximum field amplitude variation on the average J c , allowing us to include for the conductors a semi-bean approximation which allows for more realistic loss modelling results.
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- 2019
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31. Influence of thermal and electrical turn-to-turn sharing on quench protection in superconducting coils for very high density motors and generators for hybrid-electric aircraft
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M. Majoros and M.D. Sumption
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Superconductivity ,Materials science ,Solenoidal vector field ,Electromagnetic coil ,Nuclear engineering ,Contact resistance ,Electrical conductor ,Finite element method ,Power density ,Conductor - Abstract
Superconducting winding are enabling for the development of the highest power density motors and generators for aircraft use. Some of the most promising materials are YBCO coated conductors, with their $T_{c}$ of 90 K, and useful operational range up to 77 K. NASA has preliminary designs for motors with Cu stators and coated conductor based rotor coils, and is considering the type of coil assembly for the YBCO windings. A key aspect of any YBCO coil is how to protect the coil from quench in the case of the initiation of a normal zone. The growth of the normal zone is several orders of magnitude lower than that of LTS conductors, increasing the potential for coil damage. On the other hand, the much larger minimum quench energy (MQE) makes these events much less likely. The use of a no insulation (NI) method to protect again such damage has been implemented in a number of solenoidal type coils, where a relatively low layer-to-layer contact resistance allows for current redistribution and coil protection in the case of a normal zone. Here we consider its application to racetrack coils. We have modelled a coated conductor wound racetrack coil and investigated its current sharing using finite element methods. A small defect 1 mm in length is assumed in the YBCO, and the level of current sharing is explore as a function of interlayer contact resistance. A clear transition from a high level of current sharing to a low level of current sharing is seen with the change in contact resistance.
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- 2019
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32. Metal composite T-junction terminals for MW-class aerospace electric power distribution
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Timothy J. Haugan, C. Kovacs, and M.D. Sumption
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History ,Electric power distribution ,Class (set theory) ,Materials science ,business.industry ,Composite number ,Engineering physics ,Computer Science Applications ,Education ,Metal ,visual_art ,visual_art.visual_art_medium ,business ,Aerospace ,T junction - Abstract
There is a recent surge in activity to develop high power electric (or hybrid electric) aircraft. Part of this development effort is the creation of lightweight and small volume high-performance motors and airborne power transmission cables. As part of the power transmission of a distributed propulsion aircraft will be T-terminals to extract power to individual motors from a “main” power cable. In this research, a standard pressed plate high purity Cu T-terminal, with cylindrical high-temperature superconducting cables (main cable current of 20 kA, branch cable current of 2.5 kA), were investigated using Multiphysics simulations. Then, a more geometrically optimized high purity Al-Cu composite T-terminal was simulated under similar conditions. Discussed are the influence of T-junction geometry, operating temperature (30 to 50 K), contact resistance, and magnetoresistance on joule losses of terminals with different masses. It is shown the Al-Cu terminal can greatly reduce joule losses/mass of the T-terminal while also having an intrinsic clamping force from thermal expansion of the Al shell of the composite structure.
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- 2021
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33. The strong influence of Ti, Zr, Hf solutes and their oxidation on microstructure and performance of Nb3Sn superconductors
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J Rochester, X. Xu, M.D. Sumption, Jinwoo Hwang, Jaeyel Lee, G.A. Calderon Ortiz, and X. Peng
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Superconductivity ,Flux pinning ,Materials science ,Mechanical Engineering ,Alloy ,Metals and Alloys ,Oxide ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Microstructure ,01 natural sciences ,Grain size ,0104 chemical sciences ,chemistry.chemical_compound ,chemistry ,Mechanics of Materials ,Chemical physics ,Volume fraction ,Materials Chemistry ,engineering ,0210 nano-technology ,Internal oxidation - Abstract
Over the last few years a new type of Nb3Sn superconducting composite based on the internal oxidation approach has emerged and has demonstrated performance significantly superior to conventional Nb3Sn. It requires a supply of O and the use of a Nb alloy – Nb-X, where X is a solute element that can be selectively oxidized to form oxide particles within the Nb3Sn. Such oxide particles not only refine Nb3Sn grain size, but also have the proper size to act as artificial pinning centers (APC) directly restraining fluxon motion, and thus dramatically improve superconducting properties. In this article we show that the size and volume fraction of the oxide particles determine both the levels of grain refinement and the shift in the peak field of the flux pinning force (Fp-B) curve. We explore the factors influencing the microstructure and properties, which we find include: selection of the solute element X, solute content, O content, and heat treatment. For the selection of X, we searched the periodic table for all promising candidates but focused down on the group-IVB elements (Ti, Zr, Hf) here as the drawability of Nb3Sn wires made from Nb-Ti, Nb-Zr, and Nb-Hf alloys has been demonstrated in the past few decades. We found that while internally oxidizing Nb-1.5 at.%Ti led to negligible grain refinement and Fp-B peak shift, Nb-Zr alloys led to much more dramatic results, and internally oxidizing Nb-Hf alloys led to the strongest grain refinement and Fp-B peak shift. For Hf alloying in particular, we compared our internal oxidation method with another method for grain refinement, which uses Hf alloying itself without oxidation, and found that internal oxidation led to much stronger grain refinement and Fp-B peak shift. We also found that higher solute content and lower reaction temperature led to stronger grain refinement and Fp-B peak shift. We conclude with a discussion of the possible mechanisms for the influence of these factors.
- Published
- 2021
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34. Development of a multi-scale simulation model of tube hydroforming for superconducting RF cavities
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M.D. Sumption, Hyun Sik Kim, Hojun Lim, Hyuk Jong Bong, and E.W. Collings
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Hydroforming ,Materials science ,Mechanical Engineering ,Constitutive equation ,Superconducting radio frequency ,Mechanical engineering ,02 engineering and technology ,Flow stress ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Finite element method ,Mechanics of Materials ,0103 physical sciences ,Ultimate tensile strength ,General Materials Science ,010306 general physics ,0210 nano-technology ,Anisotropy ,Tensile testing - Abstract
This work focuses on finite element modeling of the hydroforming process for niobium tubes intended for use in superconducting radio frequency (SRF) cavities. The hydroforming of tubular samples into SRF-relevant shapes involves the complex geometries and loading conditions which develop during the deformation, as well as anisotropic materials properties. Numerical description of the process entails relatively complex numerical simulations. A crystal plasticity (CP) model was constructed that included the evolution of crystallographic orientation during deformation as well as the anisotropy of tubes in all directions and loading conditions. In this work we demonstrate a multi-scale simulation approach which uses both microscopic CP and macroscopic continuum models. In this approach a CP model (developed and implemented into ABAQUS using UMAT) was used for determining the flow stress curve only under bi-axial loading in order to reduce the computing time. The texture of the materials obtained using orientation imaging microscopy (OIM) and tensile test data were inputs for this model. Continuum FE analysis of tube hydroforming using the obtained constitutive equation from the CP modeling was then performed and compared to the results of hydraulic bulge testing. The results show that high quality predictions of the deformation under hydroforming of Nb tubes can be obtained using CP-FEM based on their known texture and the results of tensile tests. The importance of the CP-FEM based approach is that it reduces the need for hydraulic bulge testing, using a relatively simple computational approach.
- Published
- 2017
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35. The effect of chemical pressure on the structure and properties of A2CrOsO6 (A=Sr, Ca) ferrimagnetic double perovskite
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Michael A. Susner, Adam A. Aczel, M.D. Sumption, Jiaqiang Yan, James C. Gallagher, Patrick M. Woodward, Fengyuan Yang, Ryan Morrow, Adam J. Hauser, and Jennifer R. Soliz
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Condensed matter physics ,Magnetic moment ,Magnetism ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Ion ,Inorganic Chemistry ,Magnetization ,Octahedron ,chemistry ,Ferrimagnetism ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Osmium ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Saturation (magnetic) - Abstract
The ordered double perovskites Sr2CrOsO6 and Ca2CrOsO6 have been synthesized and characterized with neutron powder diffraction, electrical transport measurements, and high field magnetization experiments. As reported previously Sr2CrOsO6 crystallizes with R 3 ¯ symmetry due to a−a−a− octahedral tilting. A decrease in the tolerance factor leads to a−a−b+ octahedral tilting and P21/n space group symmetry for Ca2CrOsO6. Both materials are found to be ferrimagnetic insulators with saturation magnetizations near 0.2 μB. Sr2CrOsO6 orders at 660 K while Ca2CrOsO6 orders at 490 K. Variable temperature magnetization measurements suggest that the magnetization of the Cr3+ and Os3+ sublattices have different temperature dependences in Sr2CrOsO6. This leads to a non-monotonic temperature evolution of the magnetic moment. Similar behavior is not seen in Ca2CrOsO6. Both compounds have similar levels of Os/Cr antisite disorder, with order parameters of η=80.2(4)% for Sr2CrOsO6 and η=76.2(5)% for Ca2CrOsO6, where η=2θ−1 and θ is the occupancy of the osmium ion on the osmium-rich Wyckoff site.
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- 2016
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36. Persistent compositions of non-stoichiometric compounds with low bulk diffusivity: A theory and application to Nb3Sn superconductors
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Jaeyel Lee, J Rochester, X. Xu, M.D. Sumption, and X. Peng
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Superconductivity ,Materials science ,Mechanical Engineering ,Metals and Alloys ,Thermodynamics ,02 engineering and technology ,Atom probe ,Composition (combinatorics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermal diffusivity ,01 natural sciences ,0104 chemical sciences ,law.invention ,Mechanics of Materials ,law ,Materials Chemistry ,Grain boundary diffusion coefficient ,Autocatalytic reaction ,0210 nano-technology ,Internal oxidation ,Stoichiometry - Abstract
Non-stoichiometric compounds may develop a composition gradient when they are formed by reactive diffusional processes. This paper reports an interesting phenomenon that in compounds with low bulk diffusivities, which rely mainly on grain boundary diffusion for their growth, the final bulk compositions may be far from equilibrium, with a very low bulk diffusivity leading to fixed (persistent) compositions – one such example is Nb3Sn, a superconductor. We investigated the microchemistry at the reactive interface using atom probe tomography to clarify the diffusion reaction mechanism for this low-bulk-diffusivity case and thus propose a theory for what determines the compound composition, using Nb3Sn as an example for concreteness. Using certain approximations, we derive an explicit analytical equation that illustrates what factors determine its composition profile. We compare our model with the known facts of Nb3Sn and see good agreement. In particular, this model predicts that internal oxidation may lead to higher Sn contents than conventional, non-oxidized Nb3Sn. Our measurements show that this is indeed true, and that the internally-oxidized Nb3Sn also has higher upper critical fields, achieving up to 28.2 T at 4.2 K. We discuss the general applicability of this model to non-stoichiometric compounds with low bulk diffusivity, and propose it as a tool to help in the design and processing of such materials for compositional control.
- Published
- 2020
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37. Enhancement of B and B in bulk MgB2 superconductors with SnO2 Additions
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M.D. Sumption, Danlu Zhang, E.W. Collings, C J Thong, and Matt A. Rindfleisch
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010302 applied physics ,Superconductivity ,Materials science ,Tin dioxide ,Transition temperature ,Doping ,Analytical chemistry ,Energy Engineering and Power Technology ,Condensed Matter Physics ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Lattice strain ,Dwell time ,chemistry.chemical_compound ,Lattice constant ,chemistry ,0103 physical sciences ,Magnesium diboride ,Electrical and Electronic Engineering ,010306 general physics - Abstract
Three (MgB2)1-x(SnO2)x samples with x ranging from 0 to 5 wt% were prepared by the in situ route to study the effect of tin dioxide additions on the superconducting properties of MgB2 bulk materials. All of the reacted samples were slightly Mg deficient although the starting Mg:B precursor powder ratio was 1:2. A heat treatment (HT) temperature of 700 °C with a dwell time of 30 min was used. XRD results showed evidence of peak shifts for MgB2 phases with SnO2 addition. The magnitude of the a-axis lattice constant change (0.361 ± 0.075 %) calculated for the 3 wt% doped samples is comparable in magnitude to that seen previously for the C-doped MgB2 bulks which exhibited enhanced BC2. The upper critical fields (BC2) and the irreversibility fields (Birr) were measured resistively in fields up to 14 T at 5 K to Tc. The best BC2 value at 20 K (15.2 T based on extrapolation) was seen for sample IS3 (x =3 wt%), and was comparable to the best BC2 values (≈ 15 T at 20 K) seen for C-doped MgB2 bulks. IS3 had a corresponding Birr = 10.8 T (20 K). The superconducting transition temperature (Tc) appeared to increase slightly with doping, although within the range of error bars (37.4 K to 37.6 K for 1.6 T BC2 increase at 20 K), in contrast to C doping which is accompanied by a significant decrease in Tc (39 K to 36 K for 3.8 % C doped MgB2 bulk). We attribute the observed increase in both BC2 and Birr for SnO2-additions to lattice strain caused by the introduction of precipitates within the grains.
- Published
- 2020
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38. Performance metrics of electrical conductors for aerospace cryogenic motors, generators, and transmission cables
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Timothy J. Haugan, J. Murphy, Michael A. Susner, and M.D. Sumption
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Superconductivity ,Power transmission ,Materials science ,Electromagnetic coil ,Waste heat ,Nuclear engineering ,General Physics and Astronomy ,General Materials Science ,Thermal conduction ,Electrical conductor ,Liquid hydrogen ,Power density - Abstract
In this work we evaluate the performance of various electrical conductors, both normal-state and superconducting, at cryogenic temperatures with an eye towards motor, generator, and power transmission applications for use in all-electric and more-electric aircraft. In addition to MgB2 and YBCO superconductors, we consider high purity Cu and Al as well as carbon-nanotube (CNT) yarn. We analyze the normal-state conductors for current carrying capacity at room temperature as well as LN2 (77 K) and liquid hydrogen temperatures (20 K), where appropriate. To parameterize these materials for aerospace applications we have explored various options for defining current capacity metrics for these conductors at cryogenic temperatures. Paralleling definitions for ambient environment conductors, we first define electrical current capacity in terms of a limiting temperature rise for (i) windings directly immersed in a pool-boiling cryogen environment, and (ii) the case of thermal conduction though an epoxy winding. While neither metric is fully satisfactory, their implications are important. These results are then compared to a current capacity criterion developed in terms of a specified loss generation limit, which turns out to be a more meaningful approach. The results for these normal-state conductors operating at cryogenic temperatures are then compared to superconducting MgB2 and YBCO. After this, we consider two cases for overall system-level benefit in terms of power density, one for the case where the size of the cryogenic cooling apparatus is included, and a second case where the cooling is “free” (e.g., when liquid hydrogen is already onboard). We find total system weight reductions for the cryocooled case only for the superconducting options. If time varying magnetic fields are present, superconductor filament size must be kept small; an expression for limiting filament size is developed. For the case of “free” cooling, higher current levels are possible leading to reductions in winding size up to 16X using cryogenic normal-state conductors and values of 100–200X for superconducting options. The waste heat load is also substantially reduced because the total size of the winding is strongly reduced. This may significantly reduce the thermal management burden, a difficult problem for electric propulsion aircraft. We conclude that both superconductors and normal-state cryogenic conductors can increase power density in a case when liquid cryogen is “free”, but only superconductors can lead to total system power density increases when heat cannot be rejected to the fuel.
- Published
- 2020
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39. High performance, advanced-internal-magnesium-infiltration (AIMI) MgB2 wires processed using a vapor-solid reaction route
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E.W. Collings, M A Rindfleisch, F Wan, Michael Tomsic, M.D. Sumption, and C J Thong
- Subjects
Superconductivity ,Materials science ,Magnesium ,Metals and Alloys ,chemistry.chemical_element ,Solid reaction ,Condensed Matter Physics ,Infiltration (HVAC) ,Infiltration route ,Reaction layer ,chemistry ,Materials Chemistry ,Ceramics and Composites ,Critical current ,Electrical and Electronic Engineering ,Composite material - Abstract
MgB2 superconducting wires made using a Mg infiltration method have reached a higher performance than either in-situ or ex-situ mixed powder based routes. Indeed, very high layer Jc coupled with whole-strand Je (critical current per total strand cross section) exceeding 104 A cm-2 at 4.2 K, 10 T have been found for monocore MgB2 wires. However, previous multicore infiltration route wires have not reached their potential for Je due to partially reacted and non-uniform MgB2 layers. This study shows that 18-core MgB2 AIMI wires processed using a low temperature route can attain higher and more uniform Je values due to a more uniform MgB2 reaction layer. The formation of fully reacted, uniform MgB2 layers is attributed to the switch from a liquid-solid to a vapor-solid reaction route.
- Published
- 2020
- Full Text
- View/download PDF
40. Increased flux pinning force and critical current density in MgB2 by nano-La2O3 doping
- Author
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M.D. Sumption, C J Thong, Danlu Zhang, Mike Tomsic, F Wan, Matt Rindfleisch, and E.W. Collings
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Superconductivity ,Magnetization ,Materials science ,Flux pinning ,chemistry ,Electrical resistivity and conductivity ,Doping ,Nano ,Analytical chemistry ,chemistry.chemical_element ,Boron ,Article ,Grain size - Abstract
MgB2 superconducting wires and bulks with nano-La2O3 addition have been studied. A series of MgB2 superconducting bulk samples with nano-La2O3 addition levels of 0, 5, 7, 18wt% were prepared. AC resistivity data showed slight increases of Bc2 and unchanged Birr for the bulk samples with doping levels lower than 7 wt% and decreased critical fields for the heavily doped (18 wt%) bulk. X-ray diffraction (XRD) showed the presence of LaB6 in the nano-La2O3 doped MgB2 bulk samples and decreased MgB2 grain size in nano-La2O3 doped bulks. Monocore powder-in-tube (PIT) MgB2 wires without and with 5 wt% nano-La2O3 addition (P-05) were prepared for transport property measurement. 2mol%C-doped Specialty Materials Inc. (SMI) boron powder was used for wire P-05 and previously prepared control wires (control wires were made without the addition of nano-La2O3 powder, W-00 and P2). Low field magnetic properties were obtained from magnetization loop (M–H), transport critical current density (Jc) was measured at 4.2 K for the nano-La2O3 doped PIT wire (P-05) and the control samples (P2 and W-00). The transport critical current density Jc (B) of P-05 at 4.2 K and 8 T (6.0 ×104 A/cm2) was twice that of the control wire. The critical magnetic fields (Bc2 and Birr ) of P-05 and the control sample P2 were compared. The critical fields of P-05 were slightly less than those of P2. Kramer-Dew-Hughes plots indicated a change from surface pinning to a mixture of volume pinning and surface pinning. It is shown that enhancement of P-05’s transport properties is due to additional flux pinning by the fine-size rare-earth borides rather than enhanced Bc2 or Birr.
- Published
- 2020
- Full Text
- View/download PDF
41. The Role of CHPD and AIMI processing on enhancing JC and transverse connectivity of in-situ MgB2 strand
- Author
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M.D. Sumption, E.W. Collings, F Wan, and M A Rindfleisch
- Subjects
In situ ,Transverse plane ,Materials science ,Composite material ,Porosity - Abstract
Research into in-situ MgB2 strand has been focused on improvements in JC through reduction of porosity. Both of cold-high-pressure-densification (CHPD) and advanced-internal-magnesium-infiltration (AIMI) techniques can effectively remove the voids in in-situ MgB2 strands. This study shows the nature of the reduced porosity for in-situ MgB2 strands lies on increases in transverse grain connectivity as well as longitudinal connectivity. The CHPD method bi-axially applying 1.0 GPa and 1.5 GPa yielded 4.2 K J CM║s of 9.6 × 104 A/cm2 and 8.5 × 104 A/cm2 at 5 T, respectively, with compared with 6.0 × 104 A/cm2 for typical powder-in-tube (PIT) in-situ strand. Moreover, AIMI-processed monofilamentary MgB2 strand obtained even higher J Cs and transverse grain connectivity than the CHPD strands.
- Published
- 2020
- Full Text
- View/download PDF
42. Recent Progress with APC $Nb_3Sn$ Conductors
- Author
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Xingchen Xu, M.D. Sumption, Zuan Peng, and J Rochester
- Subjects
Materials science ,Fermilab ,Electrical conductor ,Engineering physics - Published
- 2018
- Full Text
- View/download PDF
43. AC Loss of Superconducting Materials in Motors and Generators for Very High Density Motors and Generators for Hybrid-Electric Aircraft
- Author
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M.D. Sumption
- Subjects
Superconductivity ,020301 aerospace & aeronautics ,Materials science ,0203 mechanical engineering ,0103 physical sciences ,High density ,02 engineering and technology ,Electric aircraft ,010306 general physics ,01 natural sciences ,Automotive engineering - Published
- 2018
- Full Text
- View/download PDF
44. Influence of Compaction During Reaction Heat Treatment on the Interstrand Contact Resistances of Nb 3Sn Rutherford Cables for Accelerator Magnets
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Milan Majoros, M.D. Sumption, Edward Collings Collings, Konstantin Yagotyntsev, D.R. Dietderich, Xiaorong Wang, Arend Nijhuis, and Energy, Materials and Systems
- Subjects
Interstrand contact resistance ,General Physics ,Materials science ,Magnetic field measurement ,Nb3Sn Rutherford cables ,Superconducting magnet ,01 natural sciences ,Magnetic cores ,chemistry.chemical_compound ,Nb3Sn strands ,0103 physical sciences ,Superconducting magnets ,Niobium-tin ,Electrical and Electronic Engineering ,010306 general physics ,Quadrupole magnet ,Nb3Sn accelerator magnets ,010302 applied physics ,Large Hadron Collider ,Condensed matter physics ,Superconducting cables ,Materials Engineering ,Coupling (probability) ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Core (optical fiber) ,Dipole ,chemistry ,Magnet ,interstrand contact resistance ,Cable insulation - Abstract
The high field superconducting magnets required for ongoing and planned upgrades to the Large Hadron Collider (LHC) will be wound with Nb3Sn Rutherford cables for which reason studies of Nb3Sn strand, cable, and magnet properties will continue to be needed. Of particular importance is field quality. The amplitudes of multipoles in the bore fields of dipole and quadrupole magnets, induced by ramp-rate-dependent coupling currents, are under the control of the interstrand contact resistances—crossing-strand, $R_{c}$ , adjacent strand, $R_{a}$ , or a combination of them, $R_{{\text{eff}}}$ . Although two decades ago it was agreed that for the LHC $R_{c}$ should be in the range 10–30 μ Ω, more recent measurements of LHC quadrupoles have revealed $R_{c}$ values ranging from 95 to 230 μ Ω. This paper discusses ways in which these values can be achieved. In a heavily compacted cable $R_{{\text{eff}}}$ can be tuned to some predictable value by varying the width of an included stainless steel (effectively “insulating”) core. But cables are no longer heavily compacted with the result that the crossing strands of the impregnated cable are separated by a thick epoxy layer that behaves like an insulating core. If a stainless steel core is actually present, $R_{{\text{eff}}}$ must be independent of core width. Since there is no guarantee that a fixed predetermined amount of interlayer separation could be reproduced from winding to winding it would be advisable to include a full width core.
- Published
- 2018
- Full Text
- View/download PDF
45. Bulge testing of copper and niobium tubes for hydroformed RF cavities
- Author
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E.W. Collings, M.D. Sumption, Hyun Sik Kim, Hojun Lim, and M. A. Susner
- Subjects
Hydroforming ,Materials science ,High energy particle ,Mechanical Engineering ,Metallurgy ,Superconducting radio frequency ,Astrophysics::Cosmology and Extragalactic Astrophysics ,02 engineering and technology ,Condensed Matter Physics ,01 natural sciences ,Finite element method ,020303 mechanical engineering & transports ,0203 mechanical engineering ,Mechanics of Materials ,0103 physical sciences ,Ultimate tensile strength ,General Materials Science ,Composite material ,Deformation (engineering) ,010306 general physics ,Astrophysics::Galaxy Astrophysics ,Residual-resistance ratio ,Tensile testing - 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.
- Published
- 2016
- Full Text
- View/download PDF
46. Microstructures and superconducting properties of high performance MgB2 thin films deposited from a high-purity, dense Mg–B target
- Author
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M.D. Sumption, G Z Li, E.W. Collings, M. A. Susner, and S.D. Bohnenstiehl
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Materials science ,Flux pinning ,Annealing (metallurgy) ,Analytical chemistry ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Microstructure ,Article ,Surfaces, Coatings and Films ,Pulsed laser deposition ,chemistry.chemical_compound ,Crystallography ,chemistry ,Magnesium diboride ,Grain boundary ,Thin film ,Pinning force - Abstract
High quality, c-axis oriented, MgB2 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 µm) MgB2. 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 MgB2 films to be c-axis oriented; the a-axis and c-axis lattice parameters were determined to be 3.073 ± 0.005 A and 3.528 ± 0.010 A, respectively. The superconducting critical temperature, Tc,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, Jcm , at 5 K, was 105 A/cm2 at 7.8 T; at 20 K, 105 A/cm2 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/Bc2 ). 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.
- Published
- 2015
- Full Text
- View/download PDF
47. Validation of Finite-Element Models of Persistent-Current Effects in Nb3Sn Accelerator Magnets
- Author
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Giorgio Ambrosio, M.D. Sumption, Soren Prestemon, A.K. Ghosh, G.L. Sabbi, Arno Godeke, D.R. Dietderich, Joseph DiMarco, Xingchen Xu, G.V. Velev, Maxim Marchevsky, E.W. Collings, S.A. Gourlay, Alexander V. Zlobin, Xiaorong Wang, Guram Chlachidze, and Helene Felice
- Subjects
Superconductivity ,Materials science ,Condensed matter physics ,Niobium ,chemistry.chemical_element ,Persistent current ,Particle accelerator ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Magnetic field ,Conductor ,law.invention ,Magnetization ,chemistry ,law ,Magnet ,Electrical and Electronic Engineering - 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 Nb 3 Sn accelerator magnets. Here, a finite-element method based on the measured strand magnetization is validated using three state-of-the-art Nb 3 Sn 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.
- Published
- 2015
- Full Text
- View/download PDF
48. Effects of Core Type, Placement, and Width on the Estimated Interstrand Coupling Properties of QXF-Type Nb3Sn Rutherford Cables
- Author
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D. R. Dietderich, Milan Majoros, E.W. Collings, M.D. Sumption, and X. Wang
- Subjects
Rutherford cable ,Magnetization ,Resistive touchscreen ,Materials science ,Nuclear magnetic resonance ,Condensed matter physics ,Contact resistance ,Electrical and Electronic Engineering ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials - Abstract
The coupling magnetization of a Rutherford cable is inversely proportional to an effective interstrand contact resistance R eff , a function of the crossing-strand resistance R c , and the adjacent strand resistance Ra. In cored cables, R eff 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, R eff (W) decreased smoothly as W decreased from 100%, whereas for a set of research-wound SS-cored Nb 3 Sn cables, R eff plummeted abruptly and remained low over most of the range. The difference is due to the controlling influence of R c - 2.5 μΩ for the stabrite/NbTi and 0.26 μΩ for Nb 3 Sn. The experimental behavior was replicated in the R eff (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 Nb 3 Sn cables (R c = 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) R eff decreased more gradually in cables with higher R c 's; and 3) a suitable R eff for a Nb 3 Sn cable can be achieved by inserting a suitably resistive core rather than an insulating (SS) one.
- Published
- 2015
- Full Text
- View/download PDF
49. Persistent-Current Magnetization of <tex-math notation='TeX'>$\hbox{Nb}_{3}\hbox{Sn} $</tex-math> Strands: Influence of Applied Field Angle and Transport Current
- Author
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M.D. Sumption, Xingchen Xu, Milan Majoros, and E.W. Collings
- Subjects
Materials science ,Field (physics) ,Condensed matter physics ,Magnetometer ,Persistent current ,Superconducting magnet ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,law.invention ,chemistry.chemical_compound ,Magnetization ,chemistry ,law ,Magnet ,Electrical and Electronic Engineering ,Current (fluid) ,Niobium-tin - 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 Nb 3 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 ~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.
- Published
- 2015
- Full Text
- View/download PDF
50. Reduced Magnetization and Loss in Ag–Mg Sheathed Bi2212 Wires: Systematics With Sample Twist Pitch and Length
- Author
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H. Miao, M.D. Sumption, C. S. Myers, Y. Huang, E.W. Collings, and Michael A. Susner
- Subjects
Superconductivity ,Protein filament ,Magnetization ,Materials science ,Condensed matter physics ,Field (physics) ,Continuum (design consultancy) ,Perpendicular ,Electrical and Electronic Engineering ,Twist ,Condensed Matter Physics ,Anisotropy ,Electronic, Optical and Magnetic Materials - Abstract
Suppression of magnetization and effective filament diameter deff with twisting was investigated for a series of recent Bi2212 strands manufactured by Oxford Superconducting Technologies. We measured magnetization as a function of field (out to 14 T), at 5.1 K, of twisted and nontwisted 37 × 18 double restack design strands. The samples were helical coils 5-6 mm in height and approximately 5 mm in diameter. The strand diameter was 0.8 mm. The magnetization of samples having twist pitches of 25.4, 12.7, and 6.35 mm were examined and compared to nontwisted samples of the same filament configuration. The critical state model was used to extract the 12-T d eff from magnetization data for comparison. Twisting the samples reduced d eff by a factor of 1.5-3. The d eff was shown to increase both with L and L p . Mathematical expressions, based upon the anisotropic continuum model, were fit to the data, and a parameter γ 2 , which quantifies the electrical connectivity perpendicular to the filament axis, was extracted. The bundle-to-bundle connectivity along the radial axis was found to be approximately 0.2%. The d eff was substantially reduced with L p . In addition, the importance of understanding sample length dependence for quantitative measurements is discussed.
- Published
- 2015
- Full Text
- View/download PDF
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