A method to evaluate cracks in a superconductive cylinder used to shield weak magnetic fields

To survey the local superconductivity and cracks in a large superconductor, a method for estimating the property from the difference in the real component ΔR and imaginary component ΔX of the complex impedance of a coil with a sample and another without one is proposed. This method was applied to two samples one which was superconductive and one not superconductive at 77.3 K. It is understood that samples become superconductive when ΔR is sufficiently near 0 and ΔX is negative. The relation between two superconductors, one without and the other with artificially induced cracks was experimentally investigated. It was confirmed that the property of the sample with cracks deviated from superconductivity. As for a superconductive cylinder of 0.5 m in diameter and 1 m in length open at one end, ΔR and ΔX at various points on the wall and at the closed end were measured at 77.3 K and the values of ΔR were sufficiently near 0. All values of ΔX were negative. The magnetic shielding effect was confirmed to be 1/20000