Design of Nb3Sn-based Superconducting Magnet for Adiabatic Demagnetisation Refrigerator

Abstract

In space, sub-Kelvin temperatures are required for the advanced and sophisticated components. Achieving extremely low temperatures is essential for both practical applications and fundamental research. The low temperature allows operations like quantum computing and the emergence of quantum states such as superfluidity and superconductivity. The sub-Kelvin temperatures are achieved by the adiabatic demagnetization refrigerators (ADRs) combined with mechanical cryocoolers. Operating adiabatic demagnetization refrigeration requires a lightweight, low-current, and uniform magnetic field superconducting magnet. This paper outlines the analytical and numerical techniques to analyse the nested shape superconducting magnet for generating high and evenly distributed magnetic fields. The superconducting magnet comprises of four coaxial formers with an inner bore diameter of 35 mm and a former length of 60 mm. To generate a central magnetic field of 3 Tesla, an electric current of 8 A is supplied through Nb3Sn superconducting wire. The Nb3Sn wire is selected for better feasibility with high current density and magnetic field for operating below 10 K temperature. An analytical analysis was executed to determine the magnetic field at the center line along the radial and axial direction of the nested coil. The numerical simulations were executed by the finite element method to estimate the magnetic field distribution in the complete domain of the coils. The results obtained by the developed analytical model with the experimental data revealed a maximum error margin of ± 10 %. The magnetic flux generated by individual coil and as a combined coil is calculated along the axial and radial directions. Additionally, the interactive effect of the current, the total number of turns, and the wire diameter of the Nb3Sn superconducting wire on the magnetic field are estimated. Further, the magnetic field variation with the current, time, and contours at different time steps are examined. Moreover, the magnetic field ratio is also estimated at different positions of the coil