The Influence of Wire Bending and Wire Diameter on Transport Critical Current Density in Small MgB2 Superconducting Coils for Applications in Multi-Section Coils

Abstract

This article presents the impact of MgB2 wire bending and diameter on transport critical current density and irreversible magnetic field of a resultant coil. Unreacted MgB2 wires 500 mm in length and 0.63 or 0.83 mm in diameter have been used in the fabrication of small diameter (14 mm) superconducting coils. The coils were subsequently annealed under isostatic pressure of 1 GPa for 15 min at 700 °C and 725 °C. Our results indicate that larger wire diameter, higher annealing temperature, and bending lead to slight reduction of critical current density and irreversible magnetic field in the coil.

Effect of Low Annealing Temperature on the Critical-Current Density of 2% C-Doped MgB2 Wires Used in Superconducting Coils with the Wind-and-React (W&R) Method—High-Field and High-Temperature Pinning Centers

“…The next results show that small coils, after annealing at 630 °C for 2 h, had a B irr value that was 10% higher than that of a straight 2% C-doped MgB 2 wire from the same annealing process. Previous results showed that small coils and simple coils had the same B irr [ 12 ]. However, these processes were performed in liquid Mg. Our heating process for J and K coils involved solid-state Mg.…”

“…Conducted tests showed that the wind-and-react (W&R) method is much better than the react-and-wind (R&W) method, because it allows for a large bending radius of the wires (diameter 7.5 mm [ 5 ]) and reduces the amount of damage to the MgB 2 material, Nb barrier, and wire shields during the coil-winding process [ 7 , 8 , 9 , 10 , 11 ]. Studies also showed that annealing MgB 2 coils made with W&R methods under high isostatic pressure does not lead to damage to the structure of the MgB 2 material [ 12 ]. This allows for the production of high-field MgB 2 superconducting coils.…”