Effects of Differential Thermal Contraction Between the Matrix and the Filaments in Mono- and Multifilamentary Nb sub 3 Sn on the Superconducting Critical Temperature

摘要

The strain on Nb sub 3 Sn due to the differential thermal contraction between the matrix (Cu, bronze) and the filaments (Nb, Nb sub 3 Sn, Ta) of a superconducting wire is known to decrease the superconducting critical temperature T/sub c/. In order to study the effects of heat treatment conditions and filament size on the degradation of T/sub c/ by the strain. T/sub c/ for monofilamentary wires ((Nb sub 3 Sn and bronze in Ta) in Cu matrix, and (bronze in Nb tubings) in Cu matrix) were measured for heat-treating periods in of 1 to 120 h at 725 exp 0 C. Several observations were made regarding the effects on T/sub c/ of thermal contraction strains from various components of the conductors. The influence of a Cu matrix on T/sub c/ was small (approx. 0.2 K). When the bronze matrix was inside Nb tubing the degradation of T/sub c/ due to strains was substantially larger than when the Nb filaments were in a bronze. Wires with smaller filament diameters achieved a maximum T/sub c/ in shorter heat treatment times than those with larger filaments. These results are discussed in terms of the critical currents of these wires under applied tensile strains. (ERA citation 05:010341)