Towards a Non-Destructive Method of Mapping the E-J Relation Using Force Decay Measurements on Superconducting Bulks

In many applications of high-temperature superconductivity, such as superconducting magnetic bearings, precise knowledge of the non-linear voltage-current (E-J) relation is necessary for making accurate quantitative predictions of performance. Magnetic microscopy allows the spatial mapping of coated conductor superconducting properties. There is no equivalent spatial mapping technique for bulk superconductors. A convenient method of mapping the E-J relation for superconductor bulks to be used in superconducting magnetic bearings is desired. The maglev force in a superconducting bearing decays logarithmically over time due to flux creep. The non-linear E-J behaviour describes this flux-creep behaviour and maximum force. It should, therefore, be possible to map the E-J power law of a bulk superconductor using levitation force decay characteristics. Using the H-formulation finite-element method we have simulated the levitation force decay under zero field cooled conditions and identified a relation between the logarithmic force decay parameters and the n-index of the E-J power law. This potentially offers a non-destructive method of determining the E-J relation in large superconducting bulks.