Critical currents of silver-sheathed bismuth-based tapes at 20 K: Small coils and field orientation anisotropy in external fields up to 20 T

Abstract

Critical currents, including field orientation anisotropy, of silver-sheathed bismuth-based superconducting tapes, for both small coils and short samples, have been measured at 20 K (liquid hydrogen) in external fields up to 20 T. The performance of two small coils is consistent with the critical current data of short samples. One coil, at 20 K and in a field of 20 T, for example, produced a self field of 0.35 T (Ic=136 A; Jc=1.7×104 A/cm2). Short-sample critical current data indicate that field orientation anisotropy is more pronounced at 20 K than at 4.2 K. At 20 K and 20 T, e.g., Jc(H∥), critical current density in the parallel field orientation, is 5.23×104 A/cm2, while Jc(H⊥), critical current density in the perpendicular field orientation, is 1.75×104 A/cm2, an anisotropy factor, Jc(H⊥)/Jc(H∥), of 0.34. In the field range 2–15 T, the anisotropy factor at 20 K ranges 0.51–0.55.