Transport critical currents I c at 1 µV cm −1 and exponents n of the power law characteristics (E ∼ j n ) of single-filament Bi(2223)/Ag tapes were measured at 77 K in the self-field and in external magnetic fields up to 1.2 T. The effects of tape orientation in a transverse magnetic field from −120 • to +120 • (related to the basic state at B c-axis) were investigated as well. The values of the transport critical current I c and exponent n as well their mutual relation reflect the quality of the Josephson-linked current network connectivity at B < B * (B * is the cross-over field at which the weak-link currents cease to contribute to the transport current) and the ability of pinning centres to pin flux lines in the whole magnetic field region. The weak-link connectivity and the pinning potential are directly related to the structural state of the samples resulting from their different thermomechanical treatments. The better the structural quality, the higher the I c /n ratio. This ratio seems to reflect the effective number of intergrain connections and pinning centres.

An experimental study of Bi( 2223)-Ag tapes undergoing bending and straightening at 300 and 77 K has been performed. The special test equipment allows us to measure changes of the critical current in a short element of the tape during continual decreasing or increasing of the bending diameter at both temperatures mentioned above. Comparison of 300 and 77 K results shows the effect of the Ag sheath strength on the bending sensitivity of Bi( 2223)-Ag composite tape. Remarkable lowering of critical current degradation by bending at 77 K was observed. This offers the possibility of winding small-diameter coils with Bi(2223)-Ag tape pre-cooled by liquid nitrogen.

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