Very Large Engineering Critical Current Density Properties in a (6+1)-Structure MgB2 Superconducting Cable at 20 K

We report the fabrication process and critical current-carrying properties of a 20-m-length (6+1)-structure MgB
₂
superconducting cable with a Nb-Ti central reinforcement wire. The results suggest that the twisting process hardly degrades the critical current properties of MgB
₂
superconducting wire, when the cables are prepared by the twist and react process. Comparing the common single-filament wire (CW) with Ic of 118.4 A at 4.2 K and 4 T, the Ic of the single-filament wire extracted from the cable (EW) has almost with no change, about 116.7 A at the same conditions. Moreover, for the (6+1)-structure MgB
₂
superconducting cable, which is 2.40 mm in diameter and 45 mm in twist pitch, its critical current-carrying capability is up to about 8 kA and its engineering current density Jce reaches 2270 A/mm
²
at 20 K and self-field. This paper strongly implies that MgB
₂
superconducting cable prepared by the in situ solid-station method is very promising for large-scale engineering applications.