MgB2/Cu racetrack coil winding, insulating, and testing

A racetrack coil using MgB₂/Cu strand has been fabricated and tested for transport current density at 4.2 K in self field. The monofilamentary strand was 1.0 mm OD and insulated with S-glass braid. Eighty turns of strand (42 m) were wound onto a stainless steel former with outer dimensions 25 cm×10 cm×0.86 cm. The resulting racetrack coil was heat treated at 675°C for 30 minutes in flowing Ar. The strand, with a superconducting fraction of 26%, occupied 49% of the total coil pack cross sectional area. The coil I_c at 4.2 K and self field was 120 A (using a 1 μV/cm criterion). This led to a J_c,sc (across the whole coil) of 6.12×10⁴ A/cm², a J_e in the wire of 1.59×10⁴ A/cm², and an overall winding J_e of 7.9×10³ A/cm² at 4.2 K in self field. The n-values ranged from 17 to 56.