OPTIMIZATION OF WETTED SURFACE FRACTION OF HELICAL-COIL FOR LHD

LHD is a fusion experimental device with pool-cooled superconducting h elical coils. The transverse component of the magnetic field in the he lical coils becomes zero near Ore core of the coil and becomes higher toward the edge. On the contrary, load per unit length on each discont inuous insulator between the conductors becomes the largest at the cor e region of the coil. By changing wetted surface fraction of the condu ctors according to the strength of the field, the cryogenic stability of the coil can be enhanced without enlarging the maximum compressive stress on the insulators.