Factors Controlling the Onset of Proximity Effect Coupling (PEC) and the Influence of Pinning-Assisted Pec on M-H Loop Asymmetry in Multifilamentary Composites
An expression is developed for the onset of proximity effect coupling (PEC) in multifilamentary (MF) strands, that depends on intrinsic proximity effect (PE) properties, in particular: the normal/superconducting (N/S) boundary conditions and 4N the coherence length in N, also the MF strand geometry as well as a measurement-sensitivity criterion. This expression is applied to experimentally measured data on various NbTi/Cu and NbTi/CuMn MF composite strands and its use in the determination of N-metal coherence lengths is described. A transcendental equation for determining the PEC-onset interfilament spacing, dc, is derived. The so-called three-dimensional pinning properties of the PE coupling currents are then invoked to explain the asymmetry commonly seen out to relatively high magnetic fields in the magnetization loops of PEC MF composites as well as the “dips” or “bites” that occur in the low-field region under appropriate conditions. The results of model calculations are presented.
Unable to display preview. Download preview PDF.
- A.K. Ghosh, W.B. Sampson, E. Gregory, et al.,“Anomalous Low-Field Magnetization in Fine Filament NbTi Conductors”, IEEE Trans. Magn. MAG-23, 1724 (1987).Google Scholar
- I. Hlâsnik, S. Takâcs, V.P. Burjak, et al., “Properties of Superconducting NbTi Superfine Filament Composites with Diameters 0.1 µm”, Cryogenics 25, 558 (1985).Google Scholar
- 3.E.W. Collings, “Stabilizer Design Considerations in Fine Filament CufNbTi Composites”, Adv. Cryo. Eng. (Materials) 34, 867 (1988).Google Scholar
- G.L. Dorofejev, E.Y. Klimenko, S.V. Frolov, et al.,“Current Carrying Capacity of a Superconductor with Artificial Pinning”, Proceedings of the 9`h International Conference on Magnet Technology, Zürich (1985) pp. 564.Google Scholar
- L.R. Motowidlo, B. Zeitlin, M. Walker, et al.,“Multifilament NbTi with Artificial Pinning Centers: The Effect of Alloy and Pin Material on the Superconducting Properties”, Appl. Phys. Lett. 61, 991–993 (1992).Google Scholar
- O. Miura, K. Matsumoto, T. Tanaka, et al., “Pinning Characteristics in Multifilamentary Nb-Ti Superconducting Wires with Sub-Micrometer Filaments Introduced Artificial Pinning Centers”, Cryogenics 32, 315–322 (1992).Google Scholar
- 10.H. Liu, E. Gregory, and R.W. Cross, “Enhancements of Critical Current Density and Reduction of Proximity Coupling in Fine Filamentary NbTi with Si and Mn Alloyed Cu Matrices”, IEEE Trans. Magn. 30, 2304–2307 (1994); also, R. Cross, personal communication, 1997.Google Scholar
- 12.M.D. Sumption and S. Takâcs, “Flux Pinning in the Weak Layers of Superconducting Heterogeneous Structures”, Submitted to Physica C.Google Scholar
- 13.C. Deutscher and F.G. do Genies, “Proximity Effects”, in Superconductivity, ed. by R. D. Parks (Marcel Dekker, New York, 1969 ), Vol. 2, pp. 1005–1033.Google Scholar
- 15.E.W. Collings, K.R. Marken, Jr., and M.D. Sumption, “Design of Multifilamentary Strand for Superconducting Supercollider (SSC) Applications Reduction of Magnetizations due to Proximity Effect and Persistent Current”, in Supercollider 2, ed. by M. McAshan ( Plenum Press, N.Y., 1990 ) pp. 581–592.Google Scholar
- E.W. Collings, M.D. Sumption, K. Itoh, et al., “Second VAMAS AC Loss Measurement Intercomparison: Magnetization Measurement of Low-Frequency (Hysteretic) AC Loss in NbTi Multifilamentary Strands”, Cryogenics 37, 49–60 (1997).Google Scholar
- M.D. Sumption, H.Liu, E. Gregory, et al., “Enhanced Proximity Effect Coupling due to the Presence of a Nb Barrier in Fine NbTi Multifilamentary Composites”, Adv. Cryo. Eng. (Materials) 42, 1175–1182 (1996).Google Scholar