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 supercondu ctor, a method for estimating the property from the difference in the real component Delta R and imaginary component Delta X 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 b ecome superconductive when Delta R is sufficiently near 0 and Delta X is negative, The relation between two superconductors, one without and the other with artificially induced cracks was experimentally investi gated, It was confirmed that the property of the sample,vith cracks de viated from superconductivity. As for a superconductive cylinder of 0. 5 m in diameter and Im in length open at one end, Delta R and Delta X at various points on the wall and at the closed end were measured at 7 7.3 K and the values of Delta R were sufficiently near 0, All values o f Delta X were negative, The magnetic shielding effect was confirmed t o be 1/20000.