Strong magnetic fields are required in many fields, such as medicine (magnetic resonance imaging), pharmacy (nuclear magnetic resonance), particle accelerators (such as the Large Hadron Collider) and fusion devices (for example, the International Thermonuclear Experimental Reactor, ITER), as well as for other diverse scientific and industrial uses. For almost two decades, 45 tesla has been the highest achievable direct-current (d.c.) magnetic field; however, such a field requires the use of a 31-megawatt, 33.6-tesla resistive magnet inside 11.4-tesla low-temperature superconductor coils1, and such high-power resistive magnets are available in only a few facilities worldwide2. By contrast, superconducting magnets are widespread owing to their low power requirements. Here we report a high-temperature superconductor coil that generates a magnetic field of 14.4 tesla inside a 31.1-tesla resistive background magnet to obtain a d.c. magnetic field of 45.5 tesla—the highest field achieved so far, to our knowledge. The magnet uses a conductor tape coated with REBCO (REBa2Cu3Ox, where RE = Y, Gd) on a 30-micrometre-thick substrate3, making the coil highly compact and capable of operating at the very high winding current density of 1,260 amperes per square millimetre. Operation at such a current density is possible only because the magnet is wound without insulation4, which allows rapid and safe quenching from the superconducting to the normal state5,6,7,8,9,10. The 45.5-tesla test magnet validates predictions11 for high-field copper oxide superconductor magnets by achieving a field twice as high as those generated by low-temperature superconducting magnets.
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The data that support the findings of this study are available from the corresponding author upon reasonable request.
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We are grateful to many for help in the coil construction phase, including B. Jarvis (winding), P. Noyes (testing), S. Bole and G. Miller (design), and D. Hazelton at SuperPower Inc. for helping to procure this special coated conductor from early production. This work was performed at the National High Magnetic Field Laboratory, which is supported by National Science Foundation Cooperative Agreement DMR-1644779 and the State of Florida. A part of S.H.’s analysis work was supported by the Samsung Research Funding and Incubation Center of Samsung Electronics under project number SRFC-IT1801-09 and the National Research Foundation of Korea as part of the Mid-Career Research Program (number 2018R1A2B3009249).
The authors declare no competing interests.
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Extended data figures and tables
The test coils were made with the same 30-μm-thick substrate tape used in LBC3 and were built to simulate the outermost 25 turns of LBC3. The tapes in Coil A and Coil B have only one slit edge, where their orientation and position is varied from the supposed damage-free orientations of Fig. 4. Coil A is positioned with its slit edge facing inwards towards the magnet centre, whereas Coil B has the reverse and unsafe orientation. Coils A and B are placed into the same 31-T magnet used for the LBC3 coil test in a position similar to that of pancake P1, where the radial field is highest. Coil C is placed in the central field region, where the radial field is essentially zero and only hoop tension operates, mimicking the central pancakes P6 and P7.
Extended Data Fig. 2 Two-dimensional Hall magnetization maps and reconstructed transport critical current, Ic.
The maps were obtained for coils A, B and C before (top) and after (bottom) the high-field tests, and Ic was reconstructed for 77 K, B||c and 0.6 T. None of the coils was quenched. Coils A and B were cycled eight and five times, respectively, between 225–250 A in a background field of 31 T. The peak hoop strain (magnetic plus bending) was 0.27%. Coil A showed no Ic degradation, but coil B developed obvious damage on its slit edge (see circled region), which also suffered permanent rippling damage. The arrowed defects in coil B have a period matching the coil circumference, which we attribute to a periodic stress concentration. Coil C was cycled five times between 220–240 A and 240–250 A. The current was raised to 295 A at the end of the test, which corresponds to a hoop strain of 0.5%.
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Hahn, S., Kim, K., Kim, K. et al. 45.5-tesla direct-current magnetic field generated with a high-temperature superconducting magnet. Nature 570, 496–499 (2019). https://doi.org/10.1038/s41586-019-1293-1
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