Analysis of eddy current AC loss for untwisted, multifilamentary superconducting composites with various aspect ratios

AC loss was measured for several types of untwisted multifilamentary superc onducting tapes using a VSM (Vibrating Sample Magnetometer) at 4.2 K in fie lds both face-on (FO) and edge-on (EO) to the wide sides of aspected sample s. The strand types investigated were NbTi/Cu-Mn (5000 filaments), NbTi/Cu (5000 filaments), and Bi2223/Ag. The samples were typically 1-1.5 cm long, untwisted, with a wide variety of outer aspect ratios, a/b. The measured lo sses were compared to those predicted by an expression linear in a/b. From this expression, the transverse resistivity of the matrix, rho (perpendicul ar to), was extracted and compared to that determined from directly measure d RRR values, where rho (perpendicular to) = ((1+lambda)/(1-lambda))(+/-1)r ho bulk = G rho bulk While the measured losses were generally in agreement with the calculations for strand types with larger numbers of filaments, si gnificant deviations were found for strand types with smaller numbers of fi laments. Strands with lower numbers of filaments always had lower than expe cted losses, leading to a rho (perpendicular to),eff much greater than G rh o bulk, which was interpreted in terms of a reduced or "effective" eddy cur rent volume, V-f. This effect, while quite strong for these untwisted sampl es, is expected to be less pronounced in twisted samples, with some excepti ons as noted.