Present status of the high mechanical strengthened Nb3Sn superconducting wires for fusion applications

Abstract

Nb3Sn superconducting wire will become the first candidate strand material for the high current capacity conductor on the magnet of a fusion prototype reactor (DEMO). Through the ITER procurement activities, however, the current sharing temperature (Tcs) and transport critical current (Ic) degradations by the Nb3Sn filament fracture due to the huge electromagnetic force was observed, and it was pointed out that the high mechanical strengthening of Nb3Sn superconducting wire is an important research issue for a future DEMO development. Therefore, we have been reconsidering on the Nb3Sn superconducting wire fabrication process in order to satisfy with the critical current density (Jc) and mechanical strength properties for DEMO design. In the past, various reinforcing materials such as the CuNb or oxide dispersed strengthening (ODS) Cu alloys have been added to Nb3Sn superconducting wires to increase their mechanical strength.In this paper, we reviewed the typical high mechanical strengthened Nb3Sn superconducting wires with various reinforcing materials and clarify the advantages and disadvantages of the high mechanical strength method using various reinforcing materials. In addition, we have proposed the “Internal Matrix Reinforcement” as the newly high mechanical strength method without the reinforcing material for Nb3Sn superconducting wires, which concept is clearly different from the conventional high mechanical strength method using reinforce material. The commercial-like internal matrix reinforced Nb3Sn superconducting multifilamentary wires were succeeded to fabricate and the present status of their superconducting properties and mechanical strength were discussed.