Development of high current capacity mono- and 18-filament in situ MgB2 cables by varying the twist pitch
Undoped and carbon doped magnesium diboride (MgB2) cables have been assembled by braiding six Nb/Monel and Nb/Cu/stainless steel (SS) sheathed mono- and multifilament strands with a central copper stabilizer for improving the operational environment. This paper presents the fabrication and characterization of two types of in situ powder-in-tube processed mono (pure) and multifilament (carbon doped) MgB2 cables with different twist pitch lengths; thereby making them possible candidates for industrial AC applications. Critical current is not influenced by the cabling that results in various twist lengths. The total critical current of the braided cables is obtained by multiplying the critical current of six single wires without any dissipation. The critical current density (Jc) of pure (mono) and carbon doped (18-filament) six stranded cable reached 10000 A/cm2 at 5.5 and 10 T, respectively; without any observable deleterious effect caused by varying the twist pitch. The engineering current density (Je) of both cables reached the same value of 10000 A/cm2 at 3.5 and 6.5 T, respectively. Compared to the literature, this work reports some of the highest Jc and Je values for carbon doped multifilament cables that remain unaffected upon varying the twist pitch. The present results are promising in terms of scaling up these cables to industrial lengths for transformers, fault-current limiters-based applications and paves the way for the development of optimal protocols for practical functionality.