Speaker
Abstract
Real and imaginary parts of the “generalized” (a pick-up coil size dependent) nonlinear magnetic susceptibility are calculated for an arbitrary radii’s ratio α = r/R of the flat single-turn coil (r) and thin superconductive disk (R) (with thickness d << R) in the framework of the critical-state model at fundamental frequency. The results of the well-known Clem – Sanchez (CS) critical-state model for nonlinear magnetic susceptibility (h) of the superconductive disk in transverse ac field with reduced amplitude h are reproduced in the limit α → ∞. It is shown that for a standard experimental situation (specimen inside magnetometer pick-up coil) the relative systematic error of the critical current Jc measurements is negligible (< 2%) for α > 2, but tends to 25% while α → 1. On the other hand, in the case α < 1 the generalized susceptibility’s dependence on h differs qualitatively from the CS one. The Cole – Cole diagrams for generalized susceptibility are plotted for various α values.
