Recent Results on Test Windings and Coils of Bi-2212/Ag HTSC Wires
Bi2Sr2Ca1Cu2O8+x Ag and Ag-alloy sheathed multifilamentary wires of 1.0 mm diameter have been produced applying the mixed oxide technique. The wires were insulated by braiding them with a thin ceramic yarn achieving an insulation thickness of 100 µm. In order to form the superconductor the wires had to be annealed following a two step annealing procedure consisting of a partial melting followed by a long-term annealing. It could be shown that the rate of cooling after the long-term annealing distinctly influences the critical current homogeneity. Only test windings cooled at a rate exceeding 500 K/h exhibited high and sufficiently homogeneous critical currents of, e.g., 40 to 45 A (ø 1.0 mm) at 4.2 K, 9 T. This result enabled manufacturing of a first small test coil with 48 turns generating a magnetic field of 50 mT in a 9 T background magnetic field.
KeywordsFurnace Helium Sponge Calcination Bismuth
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