The European Nb3Sn advanced strand development programme

Strands relevant for fusion with high critical current densities and moderate hysteresis losses were developed and already produced on industrial scale. Based on these achievements EFDA-CSU Garching has launched a Nb₃Sn strand development and procurement action inside Europe in order to assess the current status of the Nb₃Sn strand production capability. All six addressed companies have replied positively to the strand R&D programme which includes the three major Nb₃Sn production techniques namely the bronze, internal-tin and powder-in-tube (PIT) route. According to the strand requirements for the ITER TF conductor a critical current density of 800 A/mm² (at 12 T, 4.2 K and 10 μV/m) and overall strand hysteresis losses below 500 kJ/m³ have been specified as the minimum guaranteed strand performance.The second major objective of this programme is to motivate the strand manufacturers to develop and design high performance Nb₃Sn strands optimised for the ITER conductor. For this purpose, a target critical current density of 1100 A/mm² has been added to the specification. This paper describes the strategy behind the strand development programme, the actual status of the strand production as well as first preliminary results obtained from the strand suppliers.