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The effect of Cr diffusion on the residual resistance ratio (RRR) values of [Nb.sub.3]Sn strands is studied by using the KSTAR and ITER candidate strands. The studies have shown that the RRR variation is mainly affected by the 20 K resistivity or by chrome diffusion and the other characteristics are not degraded but have rather improved.

In this paper, the superconducting properties of reacted mono- and multifilamentMgB2 wires were investigated with regards to the bending diameter via a three-point bending test using a lab-made bending test probe. The wires were manufactured by Kiswire Advanced Technology Co., Ltd. According to the results of the bending test, the tolerable bending diameters for mono- and multifilament MgB2 wires were 30 and 160 mm, respectively. In addition, the multifilament wire at a bending diameter of 150 mm showed the existence of a resistive zone caused by the "disconnection" of the MgB2 filaments due to microcracks developed across the entire wire along the transverse direction of the filament. Monofilament wires have the potential to be utilized in most superconducting applications in terms of bending diameter, whereas the bending properties of multifilament wires require improvement to facilitate the design and fabrication of multifilament MgB2 magnets. [ABSTRACT FROM AUTHOR]

Nb3Sn strands which will be used for the ITER TF coils should be chrome plated thickness of 1.8 μm to reduce AC loss and improve the thermal stability of cable. During heat treatment, the RRR value can be affected by Cr diffusion. In this work, the effect of Cr diffusion was systematically studied, using the KSTAR and ITER candidate strands. For the KSTAR strand, the Cu/non-Cu ratio was systematically varied from 1.53 to 0.69 by chemical etching whereas the samples were heat treated by the same schedule. For the ITER candidate strand, on the other hand, the Cu/non-Cu ratio was fixed to the specification value of 1.0, and the variation of the RRR value was studied with respect to the heat treatment schedule, especially the retention time of the 650°C plateau was varied from 100 to 200 hours. It was also compared with the Cr diffusion distance obtained from EPMA (Electron Probe Microanalysis). We found that the RRR value of the ITER candidate strand becomes lower than the ITER requirement of 100, if the heat treatment at 650°C is longer than 200 hours. The RRR can be reached up to 161 when the duration of 650°C plateau is reduced to 100 hours, while satisfying all other ITER requirements including the critical current density. [ABSTRACT FROM AUTHOR]