Verification Testing of ITER Nb<sub>3</sub>Sn Strand at the NHMFL

Abstract

The large quantity of Nb 3 Sn superconducting wire needed by ITER presents a significant challenge to ensure that all wires adhere to ITER specifications. The National High Magnetic Field Laboratory, USA performed verification tests for Nb 3 Sn strands used in ITER TF magnets. Converting a research laboratory into a large quantity testing facility presented many challenges in developing standard operating procedures for all the verification tests. Verification tests required by ITER include: unreacted-chrome-plated strand diameter, twist pitch and twist direction, chrome-plating thickness, unreacted-chrome-plated strand Cu-to-non-Cu volume ratio, residual resistivity ratio of Cr-plated strand (RRR), critical current at 4.22 K and 12 T (I c ), resistive transition index at 4.22 K and 12 T (n-value), and hysteresis loss per strand unit volume at 4.22 K over a ±3 T cycle. Additionally, due to the brittle nature of Nb 3 Sn superconducting wire, some samples were damaged in a controlled manner to explore the negative extremes of damage due to sample handling. We successfully completed the verification tests of ITER TF Nb 3 Sn strands made by US vendors.