Influence of loading-unloading treatment at room temperature on critical current of bronze-processed Nb 3Sn superconducting composites

Abstract

Influence of loading-unloading treatment at room temperature on critical current of bronze-processed multifilamentary Nb 3Sn superconducting composite materials were studied. The axial residual strain in Nb,Sn was predicted by the proposed simple model. In the present specimens with low volume fraction of Nb 3Sn and high tin concentration in bronze, the residual strain in Nb 3Sn at 4.2 K, which was minus (−0.65%) in the annealed condition, was raised to plus (up to +0.32%) by this treatment. According to this change in residual strain, the critical current increased but then decreased with increasing applied stress at room temperature. The variation of critical current as a function of strain in Nb 3Sn due to this treatment was considered to be essentially the same as that due to direct loading at 4.2 K, which has been reported until now. It was found that the upper critical field and critical current of tested specimens can be scaled out by the law having been found in direct loading test at 4.2 K.