High temperature superconductor cables for EU-DEMO TF-magnets

Abstract

Actual progress of High Temperature Superconductor (HTS) REBCO tapes show an enormous increase of critical current density especially at highest field. These results offer new possibilities for the application of REBCO for large fusion magnets with a magnetic field well above 13T at the conductor and a large temperature margin >10K. In parallel promising new proposals for the formation of high current HTS fusion conductors from these REBCO tapes are emerging, promising the applicability for fusion magnets, e.g. for a TF magnet of an European DEMO.The actual progress of REBCO tapes and several promising HTS fusion cable proposals will be highlighted which open the path to future high field HTS magnets for fusion. Using such REBCO tape data, calculations and modeling of a TF coil for an EU-DEMO based on the PROCESS code will be presented, showing that with today's HTS performance an EU-DEMO TF conductor is feasible, which can be operated at 4.5K with a maximum field at the conductor of approximately 13.3T (magnetic field at the plasma center approximately 6.8T) with a temperature margin of approximately 12K.Special attention will be given to a new stacked HTS conductor fabrication technique proposed by KIT which is optimized for long length production of HTS strands with high engineering current density. Due to the cross shape of the soldered superconductor stacked, this type of strand is called HTS CrossConductor or HTS CroCo. The implementation of the simple, reliable and easily scalable fabrication routine will be outlined. Measurement results of first samples show the expected critical current calculated from the individual tape opening the way to a compact kA-class HTS strands. These HTS strands can be used as a basis to build a fusion cable for a TF-coil for an EU-DEMO.