Monel contribution to AC losses in MgB$_{2}$ wires in frequencies up to 18 kHz

AC losses for a wide range of AC amplitudes and
frequencies have been studied in MgB2 superconducting wire with
36 filaments and Monel sheath at different temperatures and DC
current levels. The results show a strong nonlinear frequency
dependence below 1 kHz which crosses over to a more moderate
linear behavior at frequencies up to 18 kHz. Surprisingly, the
introduction of DC current causes a significant reduction in the
AC losses. Finite Element simulations yield AC losses consistent
with that observed experimentally. The simulations show that the
magnetic Monel sheath is a dominant source for AC losses in zero
DC current, and that non-zero DC current saturates the
magnetization, thus reducing the AC losses.