Design and construction of the helical R&D coil (TOKI-HB)

Abstract

The helical R&D coil TOKI-HB has been designed and fabricated to demonstrate the feasibility of constructing a pool-cooled superconducting helical coil extrapolatable to the Large Helical Device (LHD). In addition, the fabrication and tests of the coil will provide much needed engineering data on crucial materials and processes for the LHD. The major design parameters of the helical coil are: major radius 0.8 m, minor radius 0.2 m, helical pitch 3, coil number 1, maximum central field 0.75 T, maximum coil field 3 T, superconductor NbTi, operating current 8.93 kA and stored magnetic energy 1.9 MJ. This system consists of a helical coil wound on a hollow torus, liquid-nitrogen shields, a vacuum vessel and a control dewar. Major items of measurement plans are cool-down characteristics, cryogenic stability, stress due to the electromagnetic force, and accuracy of the magnetic field. This paper will summarize the design concept and the fabrication process of this system.