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Tripled critical current in racetrack coils made of Bi-2212 Rutherford cables with overpressure processing and leakage control

  • Author(s): Zhang, Kai
  • Higley, Hugh
  • Ye, Liyang
  • Gourlay, Steve
  • Prestemon, Soren
  • Shen, Tengming
  • Bosque, Ernesto
  • English, Charles
  • Jiang, Jianyi
  • Kim, Youngjae
  • Lu, Jun
  • Trociewitz, Ulf
  • Hellstrom, Eric
  • Larbalestier, David
  • et al.
Abstract

© 2018 IOP Publishing Ltd. We fabricated three racetrack coils (RC1, RC2, and RC3) from Bi-2212 Rutherford cables (17-strand, thickness × width = 1.44 mm × 7.8 mm, strand diameter = 0.8 mm) and applied overpressure processing heat treatment (OPHT). The quench currents of RC1 and RC2 reached 5268 A and 5781 A, respectively, despite them still, surprisingly, exhibiting some Bi-2212 leakage to the surface. After removing most of the leakages using a simple-to-implement insulation scheme, the quench current of RC3 improved to 6485 A, which is about three times the average quench current of a dozen racetrack coils that had been fabricated and reacted using the conventional 1 bar heat treatment. The results confirm the effectiveness of the OPHT technology and the new leakage control scheme for coils made from Bi-2212 Rutherford cables. Coils exhibited an increased quench current with increasing the current ramp rate from 5 to 200 A s -1 ; they were quite stable against point and transient disturbances, and were capable of adsorbing persistent Joule heating at ∼80 mW for >15 s before quenching. These behaviors are different from Nb-Ti and Nb 3 Sn accelerator magnets. Overall, our results provide a critical evaluation and verification of Bi-2212 wire and magnet technologies (wire, insulation, heat treatment, coil fabrication, and coil operation), reveal crucial new stability features of Bi-2212 magnets, and demonstrate technological options for it to become a practical high-field magnet technology.

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