Design and development of a prototype superconducting MgB₂ cable for current feeders application

Magnesium diboride (MgB₂) with TC of 39 K (1) is now widely tried in superconducting devices like magnetic resonance imaging magnets, current leads (CL), power cables etc. and have options to cool using gaseous helium, liquid hydrogen or solid nitrogen. Due to ease of availability of its raw materials, lower cost and ductile behavior, it is prominently suitable for superconducting devices operating at 5 K – 25 K under moderate magnetic fields up to 5 T. Here we report, design and development of a prototype MgB₂ cable to be used as a short link for CL application. At 25 K, it is rated to transport 3.3 kA current and at 5 K conditions it is expected to carry current up to 7 kA. It is developed using 'twist and react' technique with a cabling pattern of 6*6 MgB₂ wires and 6 number of copper wires at the core. Unreacted commercial multifilamentary composite MgB₂ wires are cabled with suitable twist pitch and then heat treated at 675 °C for 1 hour under argon environment with heating rate of 500 °C/h and cooling rate of 150 °C/h. 1-D steady state thermo-hydraulic analysis has been performed for this cable using the methodology adopted in our earlier work (2-3). Such MgB₂ cables could provide benefits of reduced mass flow rate requirement, option to cool using cold helium gas diverted from magnets feeder, higher temperature margin and cryogenics saving than that for NbTi feeder. (author)