AC critical currents of commercial Nb3Sn tapes

Quench currents and critical currents have been measured for a number of commercial Nb3Sn tapes at 4.2 K. The measurements were made at 60 Hz. The observed quench currents in the as-received tapes are considerably lower than the critical currents, which can be determined by a new technique after stabilizing material is added. The temperature dependence over the entire range above 4.2 K was measured for two of the samples. The critical current falls off approximately as 1-(T/Tc)².