rm MgB₂/rm Cu Racetrack Coil Winding, Insulating, and Testing

A racetrack coil using MgB/sub 2//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/spl times/10 cm/spl times/0.86 cm. The resulting racetrack coil was heat treated at 675/spl deg/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/sub c/ at 4.2 K and self field was 120 A (using a 1 /spl mu/V/cm criterion). This led to a J/sub c,sc/ (across the whole coil) of 6.12/spl times/10/sup 4/ A/cm/sup 2/, a J/sub e/ in the wire of 1.59/spl times/10/sup 4/ A/cm/sup 2/, and an overall winding J/sub e/ of 7.9/spl times/10/sup 3/ A/cm/sup 2/ at 4.2 K in self field. The n-values ranged from 17 to 56.