Status of Nb3Sn strand development in Korea Original Research Article

Although there were many research activities for the development of superconducting Nb3Sn strands, the major one started under KSTAR (Korea Superconducting Tokamak Advanced Research) project in 1996. After the success of a large scale production test of Nb3Sn strand using the internal tin route, a new mass production facility is under operation since 2004. KAT (Kiswire Advanced Technology Ltd.), an affiliate of Kiswire Ltd., manufactured various types of Nb3Sn strands using the internal tin process optimized for fusion magnets. For the Nb3Sn strand of the KSTAR PF coil, each module has ∼190 niobium filaments and 19 modules are restacked for the strand production. For the ITER TF strand, there are two types of basic design. One of them has 37and 19 modules with 169–219 niobium filaments in each module. The other has 19 modules with 164–190 niobium filaments in each module. Both the designs satisfy the requirements for ITER TF strand with enough margins. The characterization of the strands is performed by hysteresis loss measurement, RRR (Residual Resistivity Ratio), n-value, and critical current density measurement vs. temperature, magnetic field, and strain. The critical current density of the strands reached around 1100 A/mm2 at 12 T and 4.2 K. A well defined quality assurance program helped to produce a high quality strand with a piece length of more than 15 km. KAT has been provided Nb3Sn strand for KSTAR PF Coil and ready to produce the Nb3Sn strand for ITER TF coil. In this paper, the design concept, the fabrication procedure and the result of the strand performance test are discussed.