Novel ex situ MgB2 barrier forin situ monofilamentary MgB2 conductors with Fe and Cu sheath material

Abstract

The in situ technique for producingMgB2 conductors consists of filling a mixture of Mg powder and B powder into a tube,deformation to the shape of the conductor, and reaction at the end of the process. To maketapes by the in situ method, a low cost and ductile sheath material is needed.Unfortunately precursor powder partially reacts with a lot of materials, such as Cu, Fe andNi, which can be used as a sheath. In order to produce cheap, high-performanceMgB2 conductors a barrier able to prevent this reaction is needed. In this study ex situ MgB2 is used as this barrier. This paper compares the effectiveness of the barrier inpreventing reaction in Fe and Cu tapes heat treated under ambient pressure andunder high gas pressure conditions. It was found that this barrier is effective atpreventing reaction between Fe and B, and sufficient to prevent Cu–Mg reaction in thecase of high pressure sintering. This novel technique allows one to obtain goodJe values in a parallel field because of the possibility of achieving a high superconductor fillingfactor (in excess of 60%), which is usually very challenging in powder in tube (PIT)composite conductors with a diffusion barrier.