Temperature ramp dependent reaction kinetics of internal tin processed Nb3Sn wires

Abstract

Multifilamentary Nb3Sn wires will be a critical component of a magnetic fusion reactor, which requires a high magnetic field for confinement of the plasma. The international effort to demonstrate the feasibility of the reactor design (International Toroidal Engineering Reactor, ITER) has very stringent requirements for the hysteresis loss and the critical current density Jc(≤ 600 mJ/cm3 and ≥700 A/mm2, respectively) of the Nb3Sn wires which are to be used for the central toroidal field coil magnet. Although short wire specimens can meet these requirements, consistently fabricating long lengths of wire meeting these specifications is not trivial. A part of this inconsistency is related to the effects of the temperature ramp rate on these critical properties. Thus, to investigate the observed ramp rate dependencies a metallurgical examination was performed. Samples of wires were subjected to two controlled temperature ramp cycles. Wire cross-sections were examined from samples removed at various stages of the two ramp cycles.