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To submit residual resistance ratio (RRR) measurement method of Cu/Nb3Sn composite conductor as one of new work items to IEC-TC90 in the near future, inter-comparison tests have been carried out. Four laboratories joined the tests using the bronze-processed Cu/Nb3Sn with the external stabilizer as a sample. Laboratory W reacted and measured samples A, B and C, then they were distributed to the other three laboratories (X, Y and Z). Laboratories X, Y and Z measured samples A, B and C, respectively and those data were compared with those of W. As a result, coefficient of variation, COV, of RRR values of 6.7% was obtained. Thermoelectric voltages were also measured in the tests and it was found that it did not affect scattering of RRR measurement if we changed the polarity. If allowable target precision is extended up to around 10%, we will reach the goal of the standardization in RRR measurement method of Cu/Nb3Sn in a year.

An international round robin test of the residual resistance ratio (RRR) measurement was carried out on a Cu/Nb-Ti composite superconductor following a Working Draft for the test method prepared by Working Group 4 in IEC/TC90. Thirteen institutes from five countries participated in the round robbin test. The effect of the bending strain on the resistance at cryogenic temperatures was corrected using an empirical formula. The average and the standard deviation of RRR were 178.5 and 4.4, respectively. As a result the coefficient of variation (COV) was 2.44 %. Since the target of COV is 5 %, it is concluded that RRR can be correctly measured following the method in the Working Draft.

The residual resistance ratio (RRR) measurement method for Cu/Nb3Sn was selected to be one of the next new work proposal items for submission to IEC-TC90 in the near future. Inter-comparison tests have been carried out for some years in Japan and show that the RRR of Cu/Nb3Sn for the external Cu type is very sensitive to heat-treatment conditions and has large scattering. On the other hand, a relatively low scattering factor of under 9% was obtained in the test in which the scattering problems at heat-treatment were removed. If pre-reacted Cu/Nb3Sn is treated, the goal of the standardization in RRR measurement method will be attained before long.

Interlaboratory comparison tests of hysteresis loss measurements in Cu/Nb-Ti composite superconductors using vibrating-sample magnetometers (VSM) or SQUID magnetometers have been carried out. Two Cu/Nb-Ti wires with different filament diameters of 61 µm and 4.7 µm were prepared for the tests. The resulting coefficients of variation of hysteresis losses for 61 µm and 4.7µm wires were 5.2% and 2.6%, respectively, under the unified conditions: magnetic field amplitude of ± 1 T, measurement temperature of 4.5 K and sample length of above 30 mm. It was noted that the hysteresis losses for the 61 µm wire were strongly influenced by the sample length, whereas the losses for the 4.7 µm wire showed little influence.

For Ag sheathed Bi based (2223) phase tapes made by the powder-in-tube method, high critical current densities, Jc’s, of 66000 A/cm2 at 77K, 0T and 360000 A/cm2 at 4.2K, 0T were obtained based on the study of hardness or density in the oxide and the interface effect on Jc. Other important improvements were also achieved on the mechanical properties: Ag powders addition to oxides suppressed remarkably Jc degradation with bending after heat treatment; Ag-Al alloy sheath increased hardness, expecting high tensile strength.

We have successfully fabricated a high magnetic field coil generating 1.15T at 4.2K and 0.19T at 77.3K using Bi-based(2223) powder-in-tube method silver sheathed tape. This was accomplished by the fundamental study in the winding process and the homogenization of the critical current for a long tape sample.

TEM observations and flux creep measurements have been carried out for the Bi-Pb-Sr-Ca-Cu-O (BPSCCO) tapes, with and without the intermediate press process. A lot of dislocations were found in the grains of the pressed tape, which had 20,000 A/cm2 transport critical current density at 77 K, 0 T. Field and temperature dependence of the pinning potential U0 was summarized in ternary diagrams. It could be clearly recognized that the U0 for the BPSCCO tape was enhanced by the press. As a result, the intra-grain critical current density proved to be increased, and dislocations seemed to play a role in a pinning center.

Pb substituted BiSrCaCuO with Tc above 100 K has been studied in terms of its microstructure and superconducting properties. Transmission electron microscopic observations revealed that the caxis intergrowth structure, observed frequently in non-Pb-added Bi-Sr-Ca-Cu-O, was suppressed in the Pb introduced samples. However, lattice parameters were not obviously changed by Pb introducton and the modulation structure along the baxis still existed. The effect of the magnetic field and temperature on transport critical current density Jc exhibited Josephson junction type behavior. An example of this junction, an anisotropic crystal distribution, is shown: a highly orientated specimen showed a strong anisotropic Jc for magnetic field directions parallel and perpendicular to the pellet surface (c-plane).