Design of the high-Tc superconducting TF coil for the tight aspect ratio Tokamak power reactor (VECTOR)

The tight aspect ratio tokamak power reactor (VECTOR) is proposed as a compact fusion reactor in a cost-effective way at JAERI. In the coil system, a center solenoid is discarded from the inner side of the plasma to realize low aspect configuration and the TF coil inner leg side is a solid-like integrated center post structure. The toroidal field (TF) coil consists of 12 D-shaped coil units whose inner bores are 12 m in height and 6 m in width. The magnetic field at the plasma center is designed to be 5 T. The maximum field in winding of the TF coil is required to be 18.3 T because of low aspect ratio. The magnetic stored energy is 10.7 GJ much less than the 40 GJ for ITER. For such high field generation and high performance coil realization, a high T_c superconductor is applied to the TF coil. The coil operating current is 178 kA at 18.3 T. The structure of the TF coil unit is composed of 5 radial plates and 2 support plates unified through bolts without coil case. The radial plates are designed with "beak type" structure that its inner leg part is bent to attain high current density in winding. The conductor that is composed of high T_c superconductor strands impregnated with lead, is inserted into grooves of the radial plates. The lead plays an important role on solidification of the strands cabled and on enthalpy stabilization with its high heat capacity. For the high T_c material, Bi2212 is chosen. The operating temperature of the conductor is 20 K. The conductor is cooled indirectly from cooling plates provided between the radial plates. The conductor has the temperature margin of 3 K proofed against disturbance of 1 J/cc at 20 K.