Temperature dependence of ac losses and self-field critical currents in Nb3Sn

ac losses and self-field critical currents were measured in a Nb3Sn tape between 4.2 and 17 K. The observed dependence of losses on current at 4.2 K is adequately reproduced by assuming a surface barrier ΔH = 710 Oe and a bulk critical current density Jc = 5.7×106 A/cm2. The temperature dependence of losses above 4.2 K can also be reproduced by taking into account the observed parabolic dependence of Jc on temperature and by postulating a [1 − (T/Tc)4] dependence for ΔH. A new technique is described for measuring the critical current.