Transport critical current on Fe-sheathed MgB2 coils

Abstract

Helical windings of Fe-sheathed MgB2 wires with different dimensions were fabricated by a wind-and-react process. Wires with a cross-sectional area of 1 mm2 and 20% superconductor core were made using the powder-in-tube (PIT) method and ultra-fine starting precursors. Very good grain connectivity as well as high core density was obtained by using this method. At 20 K and self-field, the critical current of a coil with an ID of 12 mm and 12 turns was 360 A, which is equivalent to a Jc of 1.8 × 105 A cm-2. At a 6 T external magnetic field and 4.2 K, a coil with an ID of 140 mm and 10 turns possessed a Jc of 1 × 104 A cm-2. These results are a step towards the application of MgB2 wires in the temperature range of 20-30 K and high magnetic fields.