Preliminary design and analysis of 20 K helium cooled MgB2 based superconducting current feeder system for Tokamak application

Current feeders system (CFS) is one of the most critical part of a large-scale superconducting (SC) magnets based machines like a tokamak or accelerator. One end of the SC feeder is connected to magnets and another end is connected to the power supply via optimised current leads (CL) for energizing the magnets. So far, low temperature superconductor (LTS) is the popular choice for such applications. For high temperature superconductor (HTS) applications, cuprate oxide based coated conductors or magnesium diboride (MgB ₂ ) wires are the options. MgB ₂ despite of its superconducting transition temperature of 39 K,is now gaining wide attention for SC feeders system due to its lower raw material cost and ease of availability than 2G HTS tapes. To assess its suitability, we report 1-D thermo-hydraulic study of 10 kA rated MgB ₂ current feeders system cooled with 20 K helium for SST-1 tokamak as a case study. For varying mass flow rate, temperature margin along the feeder are calculated considering helium at 20 K, 4 bar (a) with cooling inlet from magnet side. Such a feeder yields a temperature margin of 6 K–16 K across its entire length depending up on mass flow rate of helium. There is also a possibility of cooling the binary current lead (HTS + MgB ₂ ) from cold helium coming out from the feeder. From our study, MgB ₂ current feeder system provides benefits of higher temperature margin, lower mass flow requirement and cryogenic savings by use of 20 K helium as coolant compared to LTS based feeders. In future, it could provide a safe, reliable and cryogenic operational cost saving solution for SC current feeders for Tokamak applications.