CRITICAL-CURRENT MODELS AND MAGNETIC SHIELDING OF HIGH-TEMPERATURE SUPERCONDUCTORS

The applicability of critical current theory to macroscopic magnetic phenomena related to the magnetic shielding ability of high temperature superconductors is discussed and some misuse of the Bean model is demonstrated. Critical current theory is used to analyze the relationships among magnetic shielding factors, breakthrough fields, the waveforms of penetrated fields, as well as their dependence on AC and DC bias fields and sample thickness. Good agreement between the waveforms of penetrated fields observed with an oscilloscope and those predicted theoretically was obtained. The axial gradient of the magnetic field in an axial direction inside a superconductor under a normal magnetic field has been analyzed both qualitatively and quantitatively. Finally. a novel experimental method to measure the distribution of the axial component of a magnetic field inside a high temperature superconductor is presented.