Critical currents for superconducting composites in the 1000-Å regime

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Abstract
Multifilamentary superconducting composites having Nb3Sn filament sizes in the 200–2000‐Å regime have been studied in magnetic fields up to 18 T. The critical currents obey Kramer’s scaling laws, and flux pinning at high fields is governed by the flux‐line lattice shear modulus C66. Despite the discontinuous nature of the filaments, the flux pinning at the field approaching Hc2 is very similar to the large‐diameter continuous filament case. The upper critical field is somewhat lower than bulk Nb3Sn as expected from the stress imposed by the bronze matrix. With the addition of a few percent Ga, Hc2 can be raised by about 2 T.