Scribing Effect on Shielding Current in REBCO Superconducting Coils

Superconducting magnets for MRI operating in subcooled liquid nitrogen at 65 K are aggressively developed with \text{Re}-{1}\text{Ba}-{2}\text{Cu}-{3}\text{O}-{7 \hbox{ - }\delta} (REBCO, Re:Rare Earth such as Y, Gd, and Eu) superconducting tapes. Superconducting magnets for MRI generally need uniformity of magnetic field within parts per million (ppm) order in time and space. The disturbance is mainly caused by the shielding current induced in the wound REBCO tapes. In this study, to solve that, multifilamentization of REBCO tapes by scribing is introduced. Two pieces of small test coils with the same dimensions and parameters were wound with nonscribed and scribed EuBCO tapes into a four-filament structure. After cooling each test coil with subcooled liquid nitrogen at 65 K and applying bias magnetic field of 0-2 T, transport current was applied step by step with an interval of several tens ampere. Magnetic field variation at the coil center was observed. Though magnetic field followed the variation of transport current with a delay in the respective coils, scribing brought about not only reduction, but also quick decay of shielding current. For quantitative analysis, a fitting expression for the observed field variations was derived and discussed.