Superconducting poloidal coils for the reacting plasma project-test results of a model coil (RPC-I) at a 200 T/sec pulsing rate and design of a new coil (RPC-II)

A model pulse coil with a stored energy of 0.45 MJ at 6 T has been built and tested in order to meet the requirements of superconducting poloidal coils of a medium size tokamak of the Reacting Plasma Project. The inner and outer diameters of the coil (RPC-I) are 19.0 and 46.8 cm, respectively, with an axial length of 41.4 cm. The pulsing test was performed by a condenser discharge method with a clamp circuit. By applying a terminal voltage of 7.0 kV, the coil was charged up to 3.84 T in 26 msec and discharged to zero with a time constant of 100 msec. The average and maximum of pulsing rates in charge-up period were 147 T/sec and 231 T/sec, respectively. The associated a.c. loss per pulse was approximately 1 kJ which was only 0.57 % of the energy stored in the coil. These results have shown for the first time the scientific feasibility of superconducting pulse coils with a pulsing rate of about 200 T/sec. As the next step, we are constructing a new coil (RPC-II) with a winding composed of wider helium cooling channels and insulation sheets between layers.