Analysis of Discharges from a High-Temperature Superconducting Magnet

A crucial component to achieve burning plasma for the next generation magnetic confinement fusion devices will be the reliable and robust high-field and possibly high-temperature superconducting magnets. Of particular importance to the advanced tokamak design is the ability of the central solenoid magnet to quickly charge up to high current level; this provides sufficient magnetic flux swing that induces a toroidal plasma current for plasma initiation. A candidate material for these magnets, Nb₃Sn, has been shown to have performance degradation under high Lorentz force that is induced when the magnet is energized at a few 10s of kilo-Amperes. Here, we use a simplified coil fabrication process to make a scaled Nb₃Sn superconducting prototype and test its current charging and discharging behaviors. In addition, the test data obtained from previous experiments on the prototype coils in collaboration with the University of Geneva are analyzed and discussed. In particular, the coil behavior at its near critical current level will reveal the coil performance limit given the simplified fabrication technique used for this coil. We address the important issues of stability, current sharing among turns, quench protection, and energy distribution within the coil winding pack.