Comparison Between Modeling and Experimental Results of Magnetic Flux Trapped in YBCO Bulks

An electromagnetic simulation of YBCO bulks was performed, and the resulting trapped magnetic flux density was compared with field cooling experimental measurements for an applied magnetic flux density up to 3 T. The simulation relied on an axisymmetric problem implementing an A-formulation of the Maxwell's equations solved by means of the finite-element method so that the time evolution of the magnetic flux density was computed over the cross section of the bulk. To derive its electrical conductivity, a classic power law was adopted that includes the dependence of the critical current density upon temperature and external magnetic field modeled on the basis of a modified Kim-Anderson relation. It was found that this model tends asymptotically toward the critical state for which the n-value becomes a free parameter that should be then estimated experimentally. The experimental results could be fairly reproduced at different operating temperatures with the best trapping at temperatures below 77 K benefiting from an increasing critical current density.