Improved Method for Determining the <inline-formula> <tex-math notation="LaTeX">$n$</tex-math> </inline-formula>-Value of HTS Bulks

Abstract

The complete penetration magnetic field $B_{P}$ is the main feature of a superconducting pellet submitted to an axial applied magnetic field. The electric $E{-}J$ characteristics of HTS bulk is generally described by a power law $E(J) = E_{C}(J/J_{C})^{n}$ . The influence of the $n$ -value and applied magnetic field rise rate $V_{b}$ on the $B_{P}$ of a HTS cylindrical pellet has been presented in a previous paper. The numerical results presented come from a numerical resolution of a nonlinear diffusion problem. With the help of these simulations, a linear relationship between $B_{P}$ , ln $V_{b}$ , and $n$ -value has been deduced. This comparison allows determining the critical current density $J_{C}$ and the $n$ -value of the power law based on direct measurement of $B_{P}$ in the gap between two bulk HTS pellets. In this paper, an improvement of this method is presented. The influence of geometric parameters $R$ and $L$ is studied to give generality to the relationship between $B_{P}$ , $V_{b}$ , and $n$ -value. A previous $B_{P}$ formula is confirmed by these new simulations. To correctly connect simulation and experimental results, the influence of spacing $e$ between bulks is studied and presented. A relationship between $B_{P}$ and measured complete penetration magnetic field $B_{PM}$ is determined.