Evaluation of residual stress and texture in isotope based Mg 11 B 2 superconductor using neutron diffraction.

Magnesium diboride (MgB 2 ) superconducting wires have demonstrated commercial potential to replace niobium-titanium (NbTi) in terms of comparable critical current density. Its higher critical temperature makes MgB 2 wire suitable for liquid-helium-free operation. We recently reported boron-11 isotope-based low-activation Mg 11 B 2 superconducting wire with decent critical current density appropriate for low-cost superconducting fusion magnets. In this study, we have mainly focused on the neutron diffraction technique to measure the residual stress in Mg 11 B 2 superconducting wire for the first time. The residual stress state was given qualitative and quantitative interpretation in terms of micro- and macrostress generation mechanisms based on the isotropic model confirmed by neutron texture measurements. The relationship between the stress/strain state in the wire and the transport critical current density is also discussed. This investigation could pave the way to further enhancement of the critical current density of low-activation Mg 11 B 2 superconducting wires suitable for next-generation fusion grade magnets.