Magnetic characteristics and AC losses of DC type-II superconductors under oscillating magnetic fields

Abstract

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|, characterizing the limits of magnetization loops that exhibit a Boolean-like behaviour. Regardless of the premagnetization state of the superconducting wire, we show how after two cycles of magnetic relaxation, boolean-like ±Mp states 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 ∆B0y(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 − i 2/3 a , 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, we have found that regardless of the nature of the transport current, either be DC or AC, 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, against the sole use of SC wires for the transmission of AC transport current, are established.

Flux front dynamics and energy losses of magnetically anisotropic 2G-HTS pancake coils under prospective winding deformations

“…As previously mentioned, although the numerical computing time for our models could be strongly reduced by simplifying the number of elements inside of each one of the superconducting domains (or HTS coil turns), by allowing a 1D strip symmetry for each one of the HTS layers, therefore eliminating the aspect-ratio problem, this comes under the expense that the physical nature of the local profiles of current density could not be observed within this approach. However, it is well know that the electromagnetic properties of type-II superconductors such as the ReBCO materials used for the manufacturing of 2G-HTS tapes are, strongly affected by the intensity and direction of externally applied magnetic fields [19,31,32], which can diminish the intensity of the critical current density, J c (B, θ) [20], or lead to rather complicated distributions of current density profiles inside the superconducting material [14,[33][34][35][36]. In fact, in order to understand the physical nature and time dependence of the local profiles of current density, which determine the overall electromagnetic properties of the coil, it is necessary to model each one of the HTS layer as a 2D system with a minimum of 2 sub-layers across their thickness, such that opposite magnetization currents can appear within each one of the HTS domains.…”

Critical State Theory for the Magnetic Coupling between Soft Ferromagnetic Materials and Type-II Superconductors

“…However, it is precisely for this geometry where a certain amount of magnetic field has been observed in regions where no transport current is expected to flow, at least under the classical conception of the CST regime for a bare SC at self-field conditions. A significant rise and drop of the local magnetic field within the SC core near the surface of the SFM sheath has also been observed [ 41 ], both of these features being in apparent disagreement with the CST, despite its largely recognized success for all known type-II superconductors [ 10 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 ].…”

“…Therefore, inspired by the pioneering research on circular magnets for high-energy particle accelerators at CERN [ 67 , 68 , 69 , 70 ] and the general CST by Badía, López and Ruiz [ 45 ], in this paper we included a multipole expansion in the integral formulation of the CST for type-II SC rounded wires [ 10 , 46 , 47 , 48 , 49 , 50 , 51 , 52 ], allowing a direct inclusion of the magnetostatic coupling between the SC and a rounded SFM sheath ( Section 2 ). In this way, we disclose the electromagnetic behavior of the current density and magnetic field resulting from the coupling of the SC and the SFM in Section 3 , explaining with semi-analytical and numerical methods the actual causes behind the increment of the AC losses in an SC-SFM cylindrical metastructure in Section 4 .…”

Why energy lossless ferromagnetic materials can add energy losses onto type-II superconductors?

“…al. 10,[55][56][57][58][59][60][61] , in this paper we extend the integral formulation of the critical state theory introduced in Ref. 45, by including a multipole fields expansion which enables the straightforward inclusion of the magnetostatic coupling between a SC and a rounded SFM sheath (Sec.…”