Suitable excitation condition in overshooting process for suppressing magnetic field attenuation in y-based coated conductor coils

In Y-based coated conductor coils, a shielding current is induced by the magnetic field component perpendicular to the broad face of the coated conductor. Since the magnetic field induced by the shielding current gradually attenuates with time, the temporally stable magnetic field required for high-resolution imaging in magnetic resonance imaging (MRI) applications is difficult to obtain. We investigated the suitable excitation conditions in an overshooting process required for suppressing the magnetic field attenuation. We fabricated a double-pancake coil composed of GdBCO tapes and measured the shielding magnetic flux density and its variation rate using Hall probes attached to the outermost layer of the coil. The variation rate of magnetic flux density decreased with the maximum coil current. The overshooting current required for zero variation rate of magnetic flux density increased with target coil current in the small coil current region, and decreased with target coil current in the large coil current region. The suitable powering conditions for the overshooting process could be obtained by considering the relationship between the final operating current of the coil, the shielding magnetic flux density, and the required overshooting current for zero field variation rates at the end of the current ramping.