Record current density of 344Amm-2 at 4.2K and 17T in CORC® accelerator magnet cables

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