Journal
SUPERCONDUCTOR SCIENCE & TECHNOLOGY
Volume 31, Issue 10, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/1361-6668/aada2f
Keywords
Bi-2212; overpressure processing; accelerator magnet; quench; HTS racetrack coil
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Funding
- Office of High Energy Physics (OHEP) of the US Department of Energy (DOE) through a US DOE Early Career Award
- Office of Science of the US DOE [DE-AC02-05CH11231]
- China Scholarship Council
- US DOE OHEP [DE-SC0010421]
- National Science Foundation [DMR-1157490]
- State of Florida
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We fabricated three racetrack coils (RC1, RC2, and RC3) from Bi-2212 Rutherford cables (17-strand, thickness x width = 1.44 mm x 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 similar to 80 mW for >15 s before quenching. These behaviors are different from Nb-Ti and Nb3Sn 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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