Proximity effects and pinning properties in superconducting wires for ac use

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In order to get a sufficient knowledge of ac loss and critical current in superconducting wires for ac use, multifilamentary superconducting wires with various filament sizes and different matrixes are investigated on their transiton temperature T_c and upper critical field B_<c2> including its temperature dependence. Much attention has been directed to the effects of filament size and matrix material to T_c and B_<c2>. Experimental resultls were analyzed in the framework of the GLAG theory. Futher, a theroretical analysis of B_<c2> in superconducting superlattices which are similar to multilayr wires in structure, has been done. Obtained results are summarized as follows.1. T_c : As the filament size df of samples is decreased from 1 mu m, T_c generally decreases from 9.35 to 7.84 K.A marked decrease in T_c appears around df=0.07 mu m and is ascribed to the proximity effect between the filament and surrounding matrix.2. B_<c2> : Values of B_<c2> at 4.2 K also decrease with decreasing df. The GL parameter Kappa GL increases with decreasing df and ranges from 40 to 60. An increase in Kappa GL for finer filament samples may lighten the decrease in B_<c2>.In superconducting superlattices where two layrs with different diffusion constants alternately pile up, values of B_<c2> parallel and perpendicular to the layr planes are appreciably different. In particular, the temperture dependence of B_<c2> parallel to the layr planes are expected to change at a temperature.