Improvement of the critical current of multifilamentary Nb3Sn conductors under tensile stress

In multifilamentary Nb3Sn conductors produced by solid state diffusion process, the Nb3Sn is subjected to a tensile stress, because the bronze contracts stronger than the Nb3Sn during cooling from the diffusion temperature to 4 K. The measurements carried out demonstrate that under externally applied tensile stress at 4 K, the critical current Icof these conductors increases and goes through a maximum Icmat a strain . This is caused by the decrease in pressure on the Nb3Sn through the external tensile stress; a further increase in the external stress leads to internal tensile stress. The compressive stress and the resulting shrinkage of the Nb3Sn increase with decreasing layer thickness, thereby Icm/Ic0increases (Ic0: initial value without strain). Icm/Ic0is solely dependent on and reaches (at 4.4 T) values above 1.4 at % for very thin Nb3Sn layers. increases as the share of Nb3Sn in the conductor cross-section decreases and accordingly behaves qualitatively as the thermally affected shrinkage of the Nb3Sn.