Comparison of ${J_{{C}}}$ in GdBCO Tape Using Dc Magnetization and Harmonic Ac Susceptibility Measurements

We have measured the critical current density (${J_{{C}}}$ ) of a sample of SuNAM HTS tape using ac susceptibility (ACS) and dc magnetization (DCM) techniques. In DCM measurements, inhomogeneity ($\delta B$) in the applied dc field causes a systematic underestimate of ${J_{{C}}}$ . The error in DCM measurements is characterized by the penetration parameter, $\gamma = \frac{{3\pi {\chi _0}\delta B}}{{({3w - \frac{{{w^2}}}{l}}){\mu _0}{J_{{C}}}}}$, and grows as ${J_{{C}}}$ decreases. Using a harmonic ACS analysis, we have obtained more accurate measurements of ${J_{{C}}}$ as a function of applied dc field and temperature for $\gamma \approx 1$.