Numerical study for critical currents in nested superconducting MgB2 coil

This numerical study presents the current density variations, local magnetic field profiles, and current-voltage curves in a nested superconducting coil with 100 mm inner diameter. The nested coil has 6 layers, and each layer contains 102 turns of MgB2/Fe wire. The nested coil is different from a conventional solenoid coil in the sense that it allows currents of different amplitudes to be applied to different layers simultaneously. This is achieved with a coil model where the individual layers are formed separately one on top of the other. The current density in superconducting domains and the magnetic field distribution within the coil are calculated by using the 2D axisymmetric model in COMSOL. The E - I and E - t curves at 20 K are obtained for each layer of the coil under the condition that magnetic field dependence of the critical current density has been taken into consid-eration. The external current is only applied to the superconducting MgB2 cores and ramped up to a level where the 100 mu V/m criterion is not exceeded excessively.