Magnetic Characteristics and AC losses of DC Type-II Superconductors Under Oscillating Magnetic Fields

Remarkable features on the magnetic moment of type-II superconducting wires of cylindrical shape, subjected to direct current conditions (DC) and transverse oscillating (AC) magnetic fields, are reported. We show how for relatively low amplitudes of the applied magnetic field, Ba, the superconducting wire rapidly develops a saturation state, |Mp|, characterising the limits of magnetisation loops that exhibit a Boolean-like ±Mp behaviour states, which can be measured during the entire period of time from which the external magnetic field B0 ranges from 0 to ±Ba, with the signs rule defined by the sign of the slope ΔB0y (t). In addition, for the practical implementation of superconducting DC wires sharing the right of way with AC lines, we report that for relatively low values of magnetic field, Ba ≤ Bp =2, being Bp the analytical value for the full penetration field in absence of transport current, Itr, the use of semi-analytical approaches for the calculation of AC-losses leads to a significant underestimation of the actual contribution of the induction losses. This phenomena is particularly relevant at dimensionless fields ba < 1-ia2/3, being ba = Ba/Bp and, ia = Ia/Ic the amplitude of an AC or DC transport current, due to the local motion of flux front profiles being dominated by the occurrence of transport current. On the other hand, regardless of the nature of the transport current, when a transverse oscillating magnetic field greater than the classical limit ba = (1 - ia) is applied to the SC wire, the difference between the obtained AC losses in both situations results to be negligible indistinctly of the approach used, semi-analytical or numerical. Thus, the actual limits from which the estimation of the AC-losses can be used as an asset for the deployment of DC SC wires sharing the right of way with AC lines.