Numerical Evaluation of the Reinforcing Effect of the Advanced YOROI Coil Structure for the HTS Coil

REBCO coils applied to superconducting magnetic energy storage system, magnetic resonance imaging, medical accelerator, and so on, are expected to result in high efficiency and compactness due to the realization of higher magnetic field and current density. Because these devices require large coil radius, huge hoop stress 'BJR' (= magnetic field × current density × coil radius) is produced in the coil winding and the damage to these devices is likely to cause. In our previous study, we proposed a novel coil structure called the Y-based oxide superconductor and reinforcing outer integrated (YOROI) structure to achieve a high-strength REBCO pancake coil. The YOROI structure comprises upper and lower plates and the outer frame of the winding outer periphery. The frames are forcibly expanded by the superconducting coil winding situated inside when the coil winding is subjected to an electromagnetic force. The outer frame is connected to the upper and lower plates and transfers a part of the electromagnetic force from the coil winding to the reinforcing outer plates. The reinforcing outer plates then support the coil to suppress the coil deformation against the electromagnetic forces. The YOROI structure achieved the resistance to a maximum hoop stress of 2 GPa, which was calculated from the BJR in an excitation test at 4.2 K in 8-T backup fields. In this study, we investigated the effect of the stress control structure to realize the HTS coil with a mechanical strength of over 2 GPa using a three-dimensional finite-element structural analysis.