Measurement of superconductor motion in R&D coil for supercooling of the LHD helical coil

A superconducting solenoid coil was constructed using a large-scale superconductor to investigate the stability of helical coil in the Large Helical Device. The coil was cooled down to 3.2-4.4 K and current of 13 kA was put in. Superconductor motion was detected directly with a high sensitivity displacement gage. At the center of the magnet, the conductor expanded to outside stably, but the conductor at the corner showed contrary and incomprehensible behavior expected the conductor rotation due to mismatching to the magnetic field.