Development of High Current Capacity Mono- and 18-Filament <italic>in situ</italic> <inline-formula> <tex-math notation="TeX">$\hbox{MgB}_{2}$</tex-math></inline-formula> Cables by Varying the Twist Pitch

Abstract

Undoped and carbon doped magnesium diboride <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$(\hbox{MgB}_{2})$</tex-math></inline-formula> 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 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> powder-in-tube processed mono (pure) and multi- filament (carbon doped) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{MgB}_{2}$</tex-math></inline-formula> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$(J_{\rm c})$</tex-math></inline-formula> of pure (mono) and carbon doped (18-filament) six stranded cable reached 10 000 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{A/cm}^{2}$</tex-math></inline-formula> at 5.5 and 10 T, respectively; without any observable deleterious effect caused by varying the twist pitch. The engineering current density <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$(J_{\rm e})$</tex-math></inline-formula> of both cables reached the same value of 10 000 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$\hbox{A/cm}^{2}$</tex-math></inline-formula> at 3.5 and 6.5 T, respectively. Compared to the literature, this work reports some of the highest <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$J_{\rm c}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="TeX">$J_{\rm e}$</tex-math></inline-formula> 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.