Determination of Jc and n-value of HTS Pellets by Measurement and Simulation of Magnetic Field Penetration

The complete penetration magnetic field BP is a feature of superconducting sample submitted to an applied magnetic field. It is very important to know it for applications like electrical motor or levitation. The electric E-J characteristics of HTS bulk is generally described by a power law. The main purpose of this paper is to investigate the influence of the n-value and applied magnetic field rise rate Vb on the BP of a HTS cylindrical pellet. The numerical results presented come from the resolution of a non linear diffusion problem with a commercial software. In this study, cylindrical HTS pellets are submitted to an axial applied magnetic field. With the help of these simulations a linear relationship between BP, Vb and n-value has been found. A comparison between measurements and simulations is done for magnetization of cylindrical bulk superconducting samples. This comparison allows to determine the critical current density JC and the n value of the power law E(J) = EC(J/JC) . The experiment is based on direct measurement of local magnetic field in the gap between two bulk HTS pellets. The field penetration measurements has been carried out on HTS pellets at 77 K by applying increasing magnetic fields with a quasi constant sweep rate for axial direction of the applied magnetic field. Two values of complete penetration magnetic field BP have been measured at two different rise rates Vb. The n-value of the real HTS pellet has been deduced.