Monel Contribution to AC Losses in MgB2 Wires in Frequencies Up To 18 kHz

AC losses for a wide range of ac amplitudes and frequencies have been studied in magnesium diboride (MgB
₂
) 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 nonzero dc current saturates the magnetization, thus reducing the ac losses.