SHORT SAMPLE TESTS OF FULL-SCALE SUPERCONDUCTING CONDUCTORS FOR LARGE HELICAL DEVICE

We have been developing superconducting conductors for the helical coils of the Large Helical Device (LHD). From the test results of scale-down R&D conductors, one conductor, KISO-4B, was selected for its simple structure and good stability. Other conductor named Design-M have been manufactured in its actual scale from the first. These two types of conductors were selected and go forward to the full-scale tests. Since both conductors have multi-layered strand cables without the transposition, it is feared that the uneven current distribution between strands may cause the degradation of the critical current. A new method of measuring the current distribution inside the conductor was introduced. A pick up 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 about the critical current and stability. From the test results of Design-M, 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.