Speaker
Description
High-temperature superconductors (HTS) are promising candidates for use in the high-field magnets needed in thermal nuclear fusion reactors. Their high critical temperatures allow them to operate at temperatures far above 4 K and ease requirements on nuclear heat generation and heating during ramping of the magnetic field. Other benefits compared to low-temperature superconductors include higher mechanical strength and the possibility to operate at high magnetic fields, exceeding 16 T. Advanced Conductor Technologies is developing HTS Conductor on Round Core (CORC®) cables and wires wound from ReBa2Cu3O7-x (ReBCO) coated tapes, for use in high-field magnet applications. HTS cables can enable demountable fusion magnets that would allow easier access to the fusion experiment for maintenance and parts replacement. CORC® cables are also developed for fusion magnets operating at currents in excess of 80 kA, requiring them to be bundled into a cable-in-conduit conductor (CICC) configuration. Major technical challenges to the use of ReBCO coated conductors in fusion magnets include the need for high current capacity magnet cables and practical, low-resistance cable joints, capable of injecting current uniformly into the many tape layers that make up the cables. Optimization steps on CORC® cables have resulted in high current terminations that have a significantly improved contact resistance with even current injection at high ramp rates exceeding 6 kA/s. Several individual joints were constructed and tested in liquid nitrogen and liquid helium to currents up to 9,000 A with contact resistances as low as 96 nΩ at 76 K and 6 nΩ at 4 K. Schemes for bundling multiple cables together into CICC conductors are being explored to enable stable 100 kA-class joints with contact resistances of less than 1 nΩ.
