Assessment of thick film YBCO for flux transformer and magnetic screening applications

Measurements on the flux creep properties of a series of thick-film YBCO tubes and rings that have been processed at a range of different temperatures are reported, and their potential for use in large-area flux transformers and shields for superconducting quantum interference device (SQUID) magnetometers is considered. It is found that films showing flux creep rates adequate for flux transformer or low-field ( approximately 100- mu T) magnetic shielding applications can be made without recourse to special doping or heat treatment techniques. Application of flux creep theory to the data and observations of the microstructure in similar films implies that the scale over which the supercurrents are flowing is on the order of tens of mm and that this would place a lower limit on fabrication accuracy. For screening the earth's magnetic field, the films reported here would be adequate; for higher fields, thicker or multiple shields may by required.<>