Electrical and mechanical limits of ex situ MgB₂ wires for cabling

Abstract

One of the aims of the SCARLET project is to develop and industrially manufacture superconducting MgB2 cables cooled by liquid Hydrogen. The ex-situ Powder-In-Tube (PIT) MgB2 wires manufactured by ASG are considered for the cable design, that can carry 20 kA DC current. These braided superconducting wires, containing brittle filaments, require high current density, thermal stability, as well as, sufficient stress tolerance, and thus the study of the electro-mechanical properties of MgB2 wires is crucial for the cable design and its functional use. Superconducting wires have to withstand all the stresses applied during the cabling process, installation, and during their operation at the temperature of around 20 K. Hence, several configurations of MgB2/Ni/Monel composite wires have been subjected to detailed electrical and mechanical characterization, which allows the estimation of the stress limits during the manufacturing of the designed cable. From these experiments, it was found that the maximal tensile stress applied to the wire at room temperature should be below 180-200 MPa, and safety bending observed for the outer filament strains was below 0.3 – 0.35 %. It is also found that the limit of the acceptable torsion (expressed by the twist pitch to wire diameter Lt/dw) is affected by the filament architecture and wire diameter and it should be above 100 for 1 mm wire and above 150 for 1.53 mm wire.