Influence of filamentary and strand aspect ratios on AC loss in short, untwisted samples of HTSC and LTSC superconducting multifilamentary composites

Measurements of magnetization, M, vs. magnetic field strength, H, have been made on HTSC Bi:2223/Ag and LTSC NbTi/matrix multifilamentary tapes as a f unction of ramp rate. The integrated loss, Q(tot), was extracted from these M-H loops, which had a maximum field amplitude of 17 kOe and ramp rates, d H/dt, ranging from 20 to 700 Oe/s. All measurements were taken at 4.2 K, wi th H directed normal and parallel, respectively, to the broad tape face. Th e samples were from 0.5 to 1.5 cm in length, and untwisted. The expressions needed to properly extract effective transverse matrix resistivities, rho( perpendicular to), are discussed and applied. In general, these expressions indicate that transverse loss in untwisted strands grows linearly with the aspect ratio, in contrast to that in twisted strands, whose losses grow wi th the square of the aspect ratio. With low aspect-ratio LTSC tapes, our eq uations gave the expected values of rho(perpendicular to). However, departu res from the expected rho(perpendicular to) emerged with further flattening of the strands as the filamentary array itself became sparse and highly as pected, and the filaments themselves became flattened. A model attributing the anomalous rho(perpendicular to) to the effects of these features is pro posed. (C) 2000 Elsevier Science B.V. All rights reserved.