Evaluation of the AC Loss Characteristics of Multifilamentary REBCO Tapes by the Mechanical Scratching of MgO Areas

AC loss is a common challenge in superconducting AC applications that increases the temperature and causes quenching, and therefore, it is crucial to reduce the AC loss. Multifilament tapes fabricated via a new method that can create a low critical current density region in the superconducting layer by scratching a buffer layer to make it multifilamentary has been proposed. However, these tapes are not completely insulated. Few studies have compared the measured AC losses of coils wound with multifilament and monofilament tapes and identified whether scaling laws are adaptable to multifilament tapes. In this study, we measure the AC losses of multifilament tapes under various conditions, such as with thinner copper layers and two-stacked pancake coils wound with them, to examine the effect of electrical coupling using a copper plate and confirm the AC loss reduction effect, respectively. These tapes are not physically separated from each other, and therefore, the AC loss is measured by varying the number of coils turns. We investigate whether the scaling laws are applicable to the multifilament tapes. The results confirm that coupling loss is present; however, the AC loss for B > 0(p) (B and B-p represent the external magnetic field amplitude and the magnet field amplitude when it penetrates the superconducting layer, respectively) is reduced sufficiently. Further, the temperature and field angle scaling law can be adapted to this multifilament tape. The AC losses of the coils wound with monofilament and multifilament tapes did not show any significant differences when the number of turns was changed.