Design of superconducting coil system for remodeling JT-60

At JAERI a plan of remodeling JT-60 tokamak fusion device by using superconducting coil system is being considered to investigate performance of break-even plasma in long pulse operation. The coil system are composed of Toroidal Field (TF), Central Solenoid (CS) and Equilibrium Field (EF) coils. The TF coil is designed to have a maximum field of 7.4 T at winding with a nominal current of 19.4 kA and a magnetic stored energy of 1.7 GJ which is larger than that of every superconducting coil constructed so far. The coil uses a cable-in-conduit conductor that a Nb₃Al (or Nb₃Sn) strand cable is inserted into a square stainless steel conduit with a circular hole and is wound with a react-and-wind technique. The design operating temperature is 4.6 K. The CS which consists of 4 modules is operated with a maximum field of 7.4 T and a maximum ramp up rate of 1.0 T/s. For the conductor, a square Nb₃Sn cable-in-conduit conductor with stainless steel conduit is used. The EF coil consists of 6 coils that the maximum size coil has an outer diameter of 11 in. The EF4 coil which has a maximum field of 7.4 T and a ramp up rate of 2.2 T/s uses the same conductor as CS and other field coils use a NbTi cable-in-conduit conductor.