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In several superconducting applications, as, for example, in some supercondcuting generators, motors, and power transmission cables, the superconductor experiences a changing magnetic field in a DC background. Simulating the losses caused by this AC ripple field is an important task from the application design point of view. In this work, we compare two formulations, the H-formulation and the minimum magnetic energy variation-formulation, based on the eddy current model (ECM) and the critical state model (CSM), respectively, for simulating ripple field losses in a DC biased coated conductor tape. Furthermore, we compare our simulation results with measurements. We investigate the frequency-dependence of the hysteresis loss predictions of the power law based ECM and verify by measurements, that in DC use, ECM clearly over-estimates the homogenization of the current density profile in the coated conductor tape: the relaxation of the local current density is not nearly as prominent in the measurement as it is in the simulation. Hence, we suggest that the power law resistivity, used as the local relation between the electric field intensity E and current density J in ECM, is not an intrinsic property of high-temperature superconductors. The difference between the models manifests itself as discrepancies in ripple field loss simulations in very low AC fields with significant DC fields or currents involved. The results also show, however, that for many practical situations, CSM and ECM are both eligible models for ripple field loss simulations. [ABSTRACT FROM AUTHOR]

Covering the edges of a Bi-2223/Ag tape conductor by a layer of soft ferromagnetic material has positive impact on its two basic performance characteristics in low magnetic fields: the critical current is improved by ∼20%, and both the magnetization and transport AC loss are reduced. Reasonable theoretical prediction of the critical current in the tape is obtained by a numerical finite-element method: the whole superconducting portion is saturated by the critical current density assumed to be anisotropic and dependent on the magnetic field. However, for the prediction of AC loss the intermediate states with partial saturation of superconductor are also significant. We studied experimentally the development of magnetic field above a common multifilamentary Bi-2223/Ag tape with edges covered by nickel during stepwise change of the transport DC current. Indirect information about the distribution of electrical current and hence the process of magnetic flux penetration and dissipation at changing the value of current can be extracted from these experiments. [ABSTRACT FROM AUTHOR]

Superconductors are strategic materials for the fabrication of magnetic shields, and within this class, MgB2 has been proven to be a very promising option. However, a successful approach to produce devices with high shielding ability also requires the availability of suitable simulation tools guiding the optimization process. In this paper, we report on a 3D numerical model based on a vector potential ( A )-formulation, exploited to investigate the properties of superconducting (SC) shielding structures with cylindrical symmetry and an aspect ratio of height to diameter approaching one. To this aim, we first explored the viability of this model by solving a benchmark problem and comparing the computation outputs with those obtained with the most used approach based on the H -formulation. This comparison evidenced the full agreement of the computation outcomes as well as the much better performance of the model based on the A -formulation in terms of computation time. Relying on this result, the latter model was exploited to predict the shielding properties of open and single capped MgB2 tubes with and without the superimposition of a ferromagnetic (FM) shield. This investigation highlighted that the addition of the FM shell is very efficient in increasing the shielding factors of the SC screen when the applied magnetic field is tilted with respect to the shield axis. This effect is already significant at low tilt angles and allows compensating the strong decrease in the shielding ability that affects the short tubular SC screens when the external field is applied out of their axis.