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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]

Levitation force is studied in a two-dimensional system consisting of an infinitely long superconductor immersed in the magnetic field created by different arrangements of infinitely long parallel permanent magnets, based on the critical-state model using the magnetic energy minimization procedure. Results on force, stability, and losses in the levitation process in this system are analyzed. [ABSTRACT FROM AUTHOR]

Fluxmetric and magnetometric demagnetizing factors Nf and Nm have been calculated using a finite-element method for rectangular prism 2a×2b×2c with susceptibility χ=-1, in the completely shielded state. Assuming the field is applied along the c dimension, the results are plotted and tabulated as functions of their aspect ratios c/a and b/max[c,a]. [ABSTRACT FROM AUTHOR]

For an infinitely long bar with rectangular cross section 2a×2b and constant susceptibility χ in a uniform transverse applied field H[sub a] along dimension a, the fluxmetric and magnetometric demagnetizing factors N[sub f,m] as functions of a/b and χ are accurately computed using a finite-elements method. By comparison of the computed results with exact analytical results for χ=-1,0,∞ and with a set of conjugate relations derived in this work, the elements distributions have been optimized to give a minimum discretization error. This error is further greatly reduced in the final results of N[sub f,m] by using an error correction approach previously proposed in a similar work for cylinders. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The force and stability of a levitating system consisting of an infinitely long superconductor and different arrangements of infinitely long parallel permanent magnets are theoretically analyzed for two different cooling processes, field and zero-field cooling, by using a model based on the critical-state model and a magnetic energy minimization procedure. The authors find that by cooling the superconductor near the magnets, one can obtain improved lateral stability as compared to the case of zero-field cooling. [ABSTRACT FROM AUTHOR]

From a theoretical analysis based on an energy minimization procedure and the critical-state model, the authors analyze the levitation of an infinitely long superconductor above infinitely long permanent magnets with different arrangements. A discussion on optimum geometries showing large levitation force and good stability is presented from the model results. [ABSTRACT FROM AUTHOR]