This paper presents a commentary on the test method for the residual resistance ratio (RRR), which is one of the most significant properties for superconductor application, of Cu/Nb-Ti composite superconductors. International standardization of the RRR has been carried forward by IEC-TC90 and now the third working draft (WD) has been prepared. The WD shows scope, definition, apparatus, data acquisition and correction of bending strain. It will be issued as IEC standard 1788-4-1 in the near future.
This paper presents a commentary on a method for testing the DC critical current of Cu/Nb-Ti composite superconductors up to 1, 000A. For direct current superconducting applications, Cu/Nb-Ti composite superconductor is the most popular material of many superconducting materials. The DC critical current is the most significant property in practical superconductors, and the establishment of this test method will contribute significantly to popularize superconductivity. Additionally we are anxious to make an immediate publication of this test method as a Japanese Industrial Standard (JIS) that corresponds to international standard IEC 61788-1, and to utilize it extensively.
This paper describes the numerical and experimental superconducting levitation forces of a single-grained Y-Ba-Cu-O bulk superconductor approximately 48mm in diameter. The experimental levitation forces were measured by changing the magnet radius systematically. It was experimentally found that the levitation force shows a maximum when the magnet radius is slightly smaller than the superconductor radius. Comparison of the experimantal and numerical levitation forces showed that even large bulk superconductors have macroscopic Jc as high as 2.0×104A/cm2, not much different from the microscopic Jc.