Effect of n-value on third harmonic voltage method analyzed by finite element method

概要

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To investigate the correctness of the estimation of the critical current density Jc in high-Tc superconductor by third harmonic voltage measurement method, the third harmonic voltage V3 and the distributions of magnetic flux and current in a superconducting film with various n-values are calculated by FEM using the n-value model. When the AC current I0cosωt is applied to a coil, the threshold coil current Ith, which is proportional to Jc in the film, is determined by so-called off-set method for V3/I0–I0 curve which is frequently used in the four terminal method. The calculated value of Ith is slightly smaller than that of theoretical value by Bean’s model. When the coil current I0 is smaller than Ith, although the current density distribution is almost uniformly distributed as predicted by Bean’s model, the value of current density is smaller than Jc. This behavior is different from the prediction of Bean’s model. It is found that the current density is uniform and is equal to Jc for high n-value when I0 is closed to Ith. Therefore, it seems to be reasonable to estimate Jc by Ith in the above method for superconducting films with n-value higher than 20.
2008-09-15