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Stable, predictable and training-free operation of superconducting Bi-2212 Rutherford cable racetrack coils at the wire current density of 1000 A/mm2.

  • Author(s): Shen, Tengming;
  • Bosque, Ernesto;
  • Davis, Daniel;
  • Jiang, Jianyi;
  • White, Marvis;
  • Zhang, Kai;
  • Higley, Hugh;
  • Turqueti, Marcos;
  • Huang, Yibing;
  • Miao, Hanping;
  • Trociewitz, Ulf;
  • Hellstrom, Eric;
  • Parrell, Jeffrey;
  • Hunt, Andrew;
  • Gourlay, Stephen;
  • Prestemon, Soren;
  • Larbalestier, David
  • et al.
Abstract

High-temperature superconductors (HTS) could enable high-field magnets stronger than is possible with Nb-Ti and Nb3Sn, but two challenges have so far been the low engineering critical current density JE, especially in high-current cables, and the danger of quenches. Most HTS magnets made so far have been made out of REBCO coated conductor. Here we demonstrate stable, reliable and training-quench-free performance of Bi-2212 racetrack coils wound with a Rutherford cable fabricated from wires made with a new precursor powder. These round multifilamentary wires exhibited a record JE up to 950 A/mm2 at 30 T at 4.2 K. These coils carried up to 8.6 kA while generating 3.5 T at 4.2 K at a JE of 1020 A/mm2. Different from the unpredictable training performance of Nb-Ti and Nb3Sn magnets, these Bi-2212 magnets showed no training quenches and entered the flux flow state in a stable manner before thermal runaway and quench occurred. Also different from Nb-Ti, Nb3Sn, and REBCO magnets for which localized thermal runaways occur at unpredictable locations, the quenches of Bi-2212 magnets consistently occurred in the high field regions over a long conductor length. These characteristics make quench detection simple, enabling safe protection, and suggest a new paradigm of constructing quench-predictable superconducting magnets from Bi-2212.

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