Development of a numerical method to determine the local E-J characteristics of anisotropic HTS from experimental V-I curves

摘要

The values of J used in E-J characteristics of HTS samples in external fields are often approximated by averaging the current over their cross-section. A model that fits these results is said to be macroscopic. Such a model suffers from the fact that it is not strictly local, as the J definition would suggest. Indeed, the macroscopic E -J characteristics consider only the external field, not the local field, which possesses an additional component: the self-field. Thus, errors will occur when applying this model to the different sample geometries and sizes that are being investigated. More convenient would be a true local E-J model that resides in a material library and could be implemented in a numerical electromagnetic analysis software. In order to achieve this goal, a numerical characterization method has been developed to obtain the local E-J characteristics. This method considers the inhomogeneous distribution of the current over the sample cross-section and its associated self-field. The latter is then added to the external field to determine the true local field. based on these calculations, an iterative non-linear curve fit is executed until self-consistence with the experimental V-I curves is achieved. The hypotheses that must be satisfied in order to obtain a valid local model are discussed for granular materials and single crystals.