Small diameter wind and react coil made of anodised Al-sheathed MgB 2 wire

This paper presents the first small diameter wind and react (W&R) coil of a single-core Al-sheathed MgB 2 wire prepared by the internal magnesium diffusion method. A heat-resistant Al 2 O 3 insulating layer 15 μ m thick was formed on the wire surface by anodic oxidation, prior to coil winding and heat treatment. A space filling factor of 0.91 was achieved for this coil, which is considerably higher than for a mica or fibre-glass insulated coil commonly used in W&R windings. The coil measurements at temperatures of 4.2 K–20 K and external fields of 1.5–8 T showed a good reliability of the Al 2 O 3 insulation to withstand the heat treatment temperature and confirmed its suitability for the W&R process. The presented results demonstrate that the Al-sheathed MgB 2 wires can be easily self-insulated and effectively used for ultra-lightweight superconducting windings with a high space filling factor and a high engineering current density.