Record current density of 344 A mm−2 at 4.2 K and 17 T in CORC® accelerator magnet cables

Abstract

One of the biggest challenges in developing conductor on round core (CORC®) magnet cables for use in the next generation of accelerator magnets is raising their engineering current density JE to approach 600 A mm−2 at 20 T, while maintaining their flexibility. One route to increase JE could be to add more RE-Ba2Cu3O7−δ coated conductors to the cable, but this would increase the cable size and reduce its flexibility. The preferred route to higher JE is a reduction in diameter of the CORC® cable, while maintaining the number of tapes wound into the cable. The availability of very thin tapes containing substrates of 30 μm thickness enabled us to wind a 5.1 mm diameter CORC® cable from 50 coated conductors, while maintaining a tape critical current Ic of about 97% after cabling. The cable Ic was 7030 A at 4.2 K in a background field of 17 T, corresponding to a JE of 344 A mm−2, which is the highest performance of any CORC® cable so far. The magnetic field dependence allowed us to extrapolate the cable performance to 20 T to predict an Ic of 5654 A and a JE of 309 A mm−2. The results clearly show that rapid progress is being made on overcoming the JE hurdle for use of CORC® cables in the next generation of accelerator magnets. Further optimization of the cable layout will likely increase JE towards 600 A mm−2 at 20 T in the near future, while further reduction in cable size will also make them even more flexible.