Energization Current Waveform to Reduce Irregular Magnetic Fields in Multi-Stacked No-Insulation REBCO Coil Systems

No-Insulation (NI) REBCO coils are being considered for application in high-field whole-body magnetic resonance imaging (MRI). In such applications, the magnetic field generated by the coil must exhibit high spatial accuracy and temporal stability. However, in NI-REBCO coils, two key factors can compromise magnetic field accuracy: (1) irregular magnetic fields caused by screening currents induced in the REBCO tape and (2) excitation delays due to radial current flow during coil energization, which occur in the NI coil winding. To address issue 1, the “overshoot method”—in which the current is initially raised above the operating level before being reduced to the target operating value—has been confirmed to improve temporal magnetic field stability. However, the effectiveness of this method may be affected by issue 2, the excitation delay specific to NI coils. In this study, we explore the two electromagnetic phenomena unique to NI-REBCO coils, investigate the effects of both the overshoot method and a modified version incorporating a plateau, and ultimately determine the optimal current waveform for improving performance.