銀シースＢｉ系２２２３銀芯付丸棒線材の交流損失

Abstract

The per-cycle AC loss properties at 77K have been investigated on the (Bi, Pb)2Sr2Ca2Cu3Ox superconducting rod-form wire with a ceramics cylinder embedded by Ag sheaths through two kinds of measuring methods. One is the transport method measuring the resistive voltage under AC transport currents and another is the magnetic method measuring the magnetization curve under AC magnetic fields. The loss values for the former are 20-50% smaller than those for the latter. This difference is explained by the anisotropy in critical current densities Jc due to a current direction that the Jc value for a longitudinal direction giving rise to the AC transport losses is larger than that for a circumferential direction to the AC magnetic losses. Apart from the difference in magnitude, the transport and magnetic losses increase with increasing frequency f at a fixed magnetic field B0 (0.2mT≤B0≤45mT) except for around the field Bp (≈5mT) for full flux-penetration, where the losses are nearly independent of f. Numerical calculations based on the critical state model show that the f dependence of the losses is caused by the losses in Ag sheath. As B0 increases, the f-dependent term due to the losses in the Ag sheath increases linearly with B02 in fields B0<<Bp, deviates from the behavior with an upward curvature at around Bp, and falls again on the B02 dependence in fields B0>>Bp. This behavior comes from the fact that the electric field in the Ag sheath is produced by magnetic flux in both the Ag sheath and the ceramic core.