Testing of full size high current superconductors in SULTAN III

The high field test facility SULTAN III in operation at PSI/Switzerland tests full size industrial prototype superconductors for fusion applications such as ITER. The facility provides a background field of up to 11 T over a length of 58 cm. A 50 kA superconducting transformer works as a very low noise current source which allows a criterion of 0.1 μV/cm to determine the superconducting to normal transition. Three 3.6 m long cable-in-conduit conductors based on both NbTi and Nb₃Sn, developed by different manufacturers, suitable for the central solenoid and toroidal field coils of ITER, have been tested so far. This paper presents the results of extensive measurements of critical current and current sharing temperature of the Nb₃Sn conductors in the 8-11 T range for temperatures between 4.5 K and 11 K. Voltage versus current curves have been analyzed with respect to the n value. The manufacturing of a high quality joint between two Nb₃Sn conductors after heat treatment is reported, together with some measurements of the joint resistance