Short sample tests of full-scale superconducting conductors for Large Helical Device

Superconducting conductors are being developed for the helical coils of the Large Helical Device (LHD). From the test results on scale-down R&D conductors, one conductor, KISO-4B, was selected for its simple structure and good stability. Another conductor, Design-M, has been manufactured in its actual scale from the first. These two types of conductors were subjected to full-scale tests. A new method of measuring the current distribution inside the conductor was introduced. A pickup coil wound on the conductor detects the magnetic flux change in the conductor longitudinal direction and becomes a sensor to measure the current distribution. Using the test facility for full-scale conductors, the Design-M conductor has been tested with regard to the critical current and stability, and the uneven current distribution from the outer layer strands to the inner layer strands inside the conductor was observed. However, no degradation of the critical current was measured.< >