H-formulation FEM modeling of the current distribution in 2G HTS tapes and its experimental validation using hall probe mapping

Abstract

One of the most widespread mathematical formulations applied to simulate the electromagnetic phenomena of coated conductor in the recent literature is the H-formulation. However, the only validation of the model has been indirect by using measurements taken from the applications, as measurements of the energy losses in ac fields, forces developed in levitation systems, or any other parameter related to a specific application. Direct validation of the calculation requires the observation of the local out-of-plane magnetic field over the surface of the sample, and it is only accessible under magneto-optical observations and, in a larger scale and better dynamic range, by the Hall scanning microscopy. We propose here the experimental validation of the H-formulation by comparing the simulated results with measurements made by a Hall probe mapping in a second-generation (2G) tape sample for several dc transported currents at 77 K. This paper presents a methodology to simulate the 2G tape by using only measured data obtained from a sample and its normalized J(B) experimental curves. Some boundary conditions that allow a faster convergence of the problem are investigated. Simulated results of the 2G tape modeled considering only the 1-mu m high-temperature superconductor (HTS) layer were compared with others that represent the most important layers of the coated conductor structure in the calculations. The simulated and measured results present a good agreement, proving that this model can calculate precisely the magnetic field and, hence, the current distribution in HTS samples.