Comparison of long and short sample critical currents in Incoloy 903 Nb3Sn cable-in-conduit conductors

Measurements of critical currents on 330 cm long, 27 strand Nb3Sn ICCS conductors indicate that compaction to 32% helium fraction in Incoloy 903 conduits does not degrade critical current. Short and long sample critical currents at 4.2 K and 1.5 μV/cm for fields from 8 to 12 T were taken to determine how well short samples predict long sample performance. Samples were made from two separate untested 27 strand cables of Oxford Airco bronze matrix Nb3Sn wire encapsulated in Incoloy 903 conduits; the cables were assumed to be identical. Voltage taps were spaced at approximately 2 cm for short samples and 330 cm for long samples. It was found that all samples were at the same state of strain. In two out of three cases, the critical currents of short samples matched those of long samples within 10%. In one case, mechanical damage to a long sample reduced its critical current relative to short samples from the same cable. Samples from the two otherwise identical cables did not yield identical critical currents, a result found to be due to different degrees of cable prereaction. Short samples are concluded to be good predictors of long sample performance as long as both have the same state of strain, the same state of prereaction, and are free of significant mechanical damage.