Bench Mark Testing of Nb₃Sn Strands for the ITER Model Coil

Abstract

The Model Coils for the ITER project (International Thermonuclear Experimental Reactor) use high performance Nb₃Sn strands with large non-Cu critical current density and moderate hysteresis losses. From the first industrial supplies of four strand types, standard specimens have been prepared at MIT and distributed to the laboratories of the four ITER Home Teams. A testing action has been carried out on identical specimens with a common test programme, including critical current, n value, hysteresis and coupling current losses, RRR, twist pitch, Cu: non-Cu ratio and Cr plating thickness. The agreement on the test results is satisfactory for most of the test items, giving evidence of reproducible procedure for sample preparation and good accuracy of the test equipment. Only for the AC losses test, the scattering of the test results is large, requiring further analyses and/or action to solve the discrepancies.