Superconducting solenoid designed for 400 kJ at 25 kA under conditions of fast discharge and field reversal

A 1.26 mH superconducting solenoid made of NbTi and Cu-CuNi mixed matrix superconductor was designed and fabricated. The coil was designed to tore 400 kJ at a current of 25 kA and was operated to currents of 20 kA. Development of high current cables and low loss superconductors are both necessary undertakings for future fusion devices. The first tests of the coil involved a very slow charge of the coil followed by a rapid discharge in 1.07 ms with a capacitor bank and a normal conductor load coil in a resonant L-C-L circuit. The second test consisted of a slow charge followed by a discharge and recharge on a time scale of a few seconds. This latter cycle resembled that expected in a Tokamak induction coil. Loss measurements were made by an electrical method during the second series of tests.