title: Isotropic round-wire multifilament cuprate superconductor for generation of magnetic fields above 30 T.
abstract: Magnets are the principal market for superconductors, but making attractive conductors out of the high-temperature cuprate superconductors (HTSs) has proved difficult because of the presence of high-angle grain boundaries that are generally believed to lower the critical current density, J(c). To minimize such grain boundary obstacles, HTS conductors such as REBa2Cu3O(7-x) and (Bi, Pb)2Sr2Ca2Cu3O(10-x) are both made as tapes with a high aspect ratio and a large superconducting anisotropy. Here we report that Bi2Sr2CaCu2O(8-x) (Bi-2212) can be made in the much more desirable isotropic, round-wire, multifilament form that can be wound or cabled into arbitrary geometries and will be especially valuable for high-field NMR magnets beyond the present 1 GHz proton resonance limit of Nb3Sn technology. An appealing attribute of this Bi-2212 conductor is that, being without macroscopic texture, it contains many high-angle grain boundaries but nevertheless attains a very high J(c) of 2,500 A mm(-2) at 20 T and 4.2 K. The large potential of the conductor has been demonstrated by building a small coil that generated almost 2.6 T in a 31 T background field. This demonstration that grain boundary limits to high Jc can be practically overcome underlines the value of a renewed focus on grain boundary properties in non-ideal geometries.
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: D C
authors.initials: DC
authors.lastname: Larbalestier
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: J
authors.initials: J
authors.lastname: Jiang
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: U P
authors.initials: UP
authors.lastname: Trociewitz
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: F
authors.initials: F
authors.lastname: Kametani
authors.affiliation: European Organization for Nuclear Research, Geneva CH-1211, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Scheuerlein
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: M
authors.initials: M
authors.lastname: Dalban-Canassy
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: M
authors.initials: M
authors.lastname: Matras
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: P
authors.initials: P
authors.lastname: Chen
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: N C
authors.initials: NC
authors.lastname: Craig
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: P J
authors.initials: PJ
authors.lastname: Lee
authors.affiliation: Applied Superconductivity Center, National High Magnetic Field Laboratory, Florida State University, 2031 East Paul Dirac Drive, Tallahassee, Florida 32310, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Hellstrom