DC and AC properties of 49-strand circular cables made of differently sheathed ultrafine MgB₂ superconducting wires

Abstract This paper reports a study of the low-temperature properties of 49-strand circular cables made of ultrafine National Institute for Materials Science MgB 2 wires. The critical currents of cables made from single-core MgB 2 wires with diameters of 0.050 mm and 0.022 mm and different sheath materials (Cu, CuNi, and Monel) were measured at temperatures from 4.2 to 35 K and external fields from 0 to 8 T. In addition, magnetization alternating current (AC) losses were measured at temperatures of 20–45 K, fields of 1–100 mT, and frequencies of 72 Hz and 144 Hz. The presented experimental results show high engineering current densities in spite of a very low filament size of 8.5 µ m and also low AC losses due to well decoupled strands. We show that the total AC losses are not only affected by the filament size but also by the sheath materials used. The cables presented here can possibly be used for small windings with low AC losses.