Temperature and Background Field Dependence of a Compact React and Wind Solenoid Coil

The manufacture of react and wind MgB₂ coils with bend diameters suitable for compact applications, such as narrow bore magnets, or demonstrators, such as generators, remains a challenge due to the finite strain tolerance of the MgB₂ filaments. One solution is to improve the conductor strain tolerance under bending by reducing the wire diameter and increasing the number of filaments. A 243-m single length of 36-filament, 0.55-mm-diameter conductor with 50-μm-thick s-glass insulation, manufactured by Hyper Tech, is continuously wound onto a 100-mm-inside-diameter, 100-mm-long, 770-turn, 5-layer solenoid coil. As a preliminary verification of short-length conductor properties, transport critical current was measured on samples as reeled. Using both dc and pulsed currents, the solenoid coil is characterized in a background field of up to 5 T, and from 4.2 K to Tc, in both liquid and vapor. Layer-by-layer instrumentation of the coil, together with short-length test data, enables voltage characteristics to be spatially determined. Dissipation in the coil was evenly distributed across all layers with a joint contact resistance of ~20 nΩ. With an inductance of 0.37 H, the coil achieved a magnetic field of 0.82 T at 22.5 K at 100 A, 415 A/mm², with no background field, and 0.32 T in a background field of 5 T at 4.2 K. The injected current values correlated with short-length critical current to within 10%.