Determination of $J_C$ and $n$-Value of HTS Pellets by Measurement and Simulation of Magnetic Field Penetration

摘要

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