✍ Scribed by S Takács
No coin nor oath required. For personal study only.
A model for calculating the resistive state of macroscopically inhomogeneous type II superconductors is presented. It is similar to the model of Warnes and Larbalestier, but in addition it includes both the properties of superconducting filaments and the surrounding normal matrix, as well as the realistic current-voltage dependence of the intrinsic superconductor. The resulting current-voltage curves are given for different intrinsic n values and for parameters of the normal matrix resembling Cu and CuNi, respectively. It is shown that the portions of the superconductor with critical currents above the most probable critical current do not contribute substantially to the induced voltage in the composite. From the measurements of the current-voltage dependence alone, one cannot, therefore, make any conclusions about the actual critical current distribution in the superconducting composite. However, the results are in accordance with the conclusions of Larbalestier and co-workers concerning the connection between the extrinsic inhomogeneities and the n value of the resistive transition. Therefore, the diagnostic tests proposed by these workers are very useful for practical purposes. In addition, a modified critical current distribution function is used for inclusion of the flux flow dissipation mechanism into the resistive state. This distribution function takes into account the restriction of the critical current value due to intrinsic or extrinsic sources. It is shown that the critical currents actually measured are close to the mean critical current of macroscopically inhomogeneous superconducting composites, in contradiction to the results of Evetts and Plummer.
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