Short sample tests of aluminum-stabilized superconductors for Large Helical Device

We have been developing aluminum-stabilized superconductors for the helical coils of the Large Helical Device (LHD). Two types of conductors, Design-M and KISO-4B, were selected to proceed to the full-scale short sample tests. The test facility for full-scale conductors consists of 100 kA vapor-cooled current leads, 9 T background field split coils, a cryostat and a 75 kA dc power supply. Since both conductors have multi-layered strand cables without transposition, it is feared that an uneven current distribution between strands may cause degradation of the critical current. To measure the current distribution inside the conductor, a new method using a pick up coil was introduced. Using this experimental setup, we have measured the critical current, the current distribution inside the conductor and the stability of both full-scale conductors.