Temperature and background field dependence of a compact react and wind MgB2 solenoid coil

Abstract

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-?m-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 n?. 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%.

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ORCID for Y. Yang: orcid.org/0000-0002-3874-6735

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