Prediction of the J_C (B) Behavior of Bi-2212 Wires at High Field

Bi-2212 wires have been produced for much of the last decade with varying architectures, powder sources, and great variability of final J_C(B) properties. As Bi-2212 transitions from an R&D materials development to a magnet technology, means to predictably forecast J_C(B) becomes increasingly valuable. Here we report on characterizations of short samples having J_C(15 T, 4.2 K) varying from 1210 to 6560 A/mm², measured in fields up to 31 T, and drawn from 10 billets. Using both 4 K transport and variable temperature vibrating sample magnetometer measurements, capable of probing the 20 K irreversibility field, B_irr = μ₀H_k, we found that the vortex pinning properties are very stable across these wires, which all used the same standard powder composition (Bi_2.17Sr_1.94Ca_0.89Cu_2.00O_8+x), even though it has been made by three different manufacturers over nine years. We conclude that a power-law fit J_C ∝ B^-α, where α = 0.280 (σ = 0.015), works well at 4.2 K over the field range of at least 3-30 T and that μ₀H_k(20 K) remains stable at 8.6 ± 0.4 T. We conclude that the dominant current limiting mechanism predicting J_C(B) in Bi-2212 is the effective filament connectivity. J_C(B) at high fields may thus be predicted by simple I_C measurements at easily accessible fields in the 3-15 T range.