AC Loss Properties of Stacked REBCO Superconducting Tapes

REBCO superconducting tapes have excellent critical current properties even at high temperature and high magnetic field. Many projects for the research and development of superconducting machines and devices with REBCO tapes are in progress worldwide. The important problem to realize them is the ac loss reduction of REBCO superconducting tapes since the most part of thermal load of cryocoolers is the ac loss. The evaluation of the induced ac loss in the windings is also quite important to design the superconducting system, especially the cooling system. In this study, we investigated the applicability of the scaling law to the stacked tapes using the currently fabricated REBCO superconducting tapes. We defined the number of stacked tapes as n, and the temperature as T. The ac loss for B_m < B_pe decreased with increasing n due to the influence of diamagnetic field, whereas the ac losses for B_mgt; B_pe agreed with each other regardless of n. By defining I_c around zero field at the respective temperature, in the respective number of stacked tapes as Ic0(T, n), I_c-B normalized by using Ic0(T, n). The normalized I_c-B curves coincided with one master curve for every n regardless of T. The normalized M-H curves and ac loss curves against the field amplitude by using Ic0(T, n) also coincided with one master curves for every n regardless of T. It was verified that the scaling law of M and ac loss was available even if the REBCO tapes stacked into multilayers.