Progress of HTS STARS Conductor Development for the Next-Generation Helical Fusion Experimental Device

A High-Temperature Superconducting (HTS) magnet is being considered to for use in the next-generation helical experimental devices. Three types of large-current HTS conductors are being developed, and one of them is the STARS (Stacked Tapes Assembled in Rigid Structure) conductor which uses HTS tapes with a simple stacking technique. Following the proof-of-principle experimental results obtained in the former 100-kA-class prototype hand-made conductor sample, an actually applicable conductor is being developed with a rated current of 18 kA at a temperature of 20 K and a magnetic field of ∼10 T. One of the crucial requirements for this conductor is to have a high current density of 80 A/mm2. In the first phase of the development, a 3-m short sample was fabricated by applying laser-beam welding to the stainless-steel jacket. It was tested in liquid nitrogen at 77 K with no external magnetic field. Then the sample was tested in gaseous helium at 20 - 40 K under a magnetic field of 6 - 8 T, and the results show that the basic requirements were satisfied