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I C axial strain dependence of high current density Nb 3 Sn conductors. Fig. 1 I C vs. strain for Mitsubishi-1400 strands soldered on different backing plates.
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IC axial strain dependence of high current density Nb3Sn conductors Fig. 1 IC vs. strain for Mitsubishi-1400 strands soldered on different backing plates. The measurement of critical current of Nb3Sn superconducting strands under axial strain in high magnetic field [IC(B, e)] is essential in the application of Nb3Sn composite to high field superconducting magnets. The large bore 20 T DC magnet at the NHMFL along with a device designed to apply tensile axial strain allows the IC(B, e) measurement of about 100 mm long straight Nb3Sn composite strand. The superconducting strands are soldered to dog-bone shaped backing plates made of different materials. The effect of the backing plate thermal contraction on the IC-e behavior is studied. Our IC-e results from samples soldered on different backing plates show that the thermal strain of Nb3Sn is approximately the thermal contraction difference between the backing plate material and Nb3Sn (see Fig. 1). A number of high JC Nb3Sn strands that will be used for the 45 T hybrid upgrade and the series-connected hybrid magnets at the NHFML are characterized using this apparatus. The upper critical field as function of strain is obtained by measuring IC-e at different fields (see Fig. 2). Our IC-e curves show significant asymmetry compared with IC-e data for low JC strands in the literature. Our data indicate severe damage in the filaments of high JC strands at large applied tensile strain. J. Lu, K. Han, R.P. Walsh, and J.R. Miller, IEEE Trans. Appl. Supercond., 17 (2), 2639 (2007). Fig. 2. IC and Bc2*(4.2 K) vs. strain for an OST strand used for the NHMFL 45 T hybrid upgrade.