AC LOSS MEASUREMENTS OF THE EXPERIMENTS ON A SINGLE INNER VERTICAL COIL (EXSIV) FOR THE LARGE HELICAL DEVICE

The AC losses of the Inner Vertical (IV) coil have been measured durin g the Experiments on a Single Inner Vertical coil (EXSIV). The IV coil s are the smallest poloidal coils of the Large Helical Device (LHD) an d their inner and outer diameters are 3.2 m and 4.2 m, respectively. T he coil consists of 16 pancake coils wound with the cable-in-conduit c onductors (CICC) whose strands are NbTi/Cu without any surface coating . The AC losses were measured with calorimetric method during excitati on tests and current shut-on tests. In addition to the usual inter-str and coupling losses with short time constants, unexpected coupling los ses were observed due to the coupling current of a long time constant.