福岡 克弘

Because the bulk-type YBCO superconductor prepared by the MPMG process characterizes high critical current density Jc, it is expected to be applied to various fields. It is important to develop measurement methods of magnetic property to the high-Tc superconductor. It is necessary to value not only DC magnetic property but also AC magnetic property. So we measured magnetic property of the high-Tc superconductor under the AC magnetic field (5-500Hz). From the experimental results we can understand that there is the first order lag element caused by the flux flow effect, and the magnetic property in low frequency is ruled by the flux flow.

Because the superconducting bulk materials have grains of various sizes, its magnetic properties are not uniform. Therefore it is necessary to develop a nondestructive measurement method to characterize the superconducting bulk materials. This paper describes measurement method of magnetic property distribution of the high temperature superconducting bulk materials.<br>We developed a magnetic field visualization system which produces visual images of the magnetic field on a computer display. The magnetic flux on the surface of YBCO bulk material under the field of -500 to 5000e was measured by this system and visualized as two dimensional graphics. The pattern of the flux distribution roughly agreed with the grain morphology. The experimental results show that this method is useful to assess the property distribution of superconducting material.

This paper describes an assessment method of magnetic property of high temperature superconducting material. The distributions of magnetic field over a surface of the superconductor were measured by the visualization technique system of magnetic field, and were demonstrated visual image on a computer display. And the property of superconductor were assessed by measuring of flux creep too. By the experimental results, these methods are useful to assess the local property of superconducting material.