New Type of Non-magnetically Sheathed MgB2 Wires—First Sight to AC Losses with Numerical Simulations

AC losses of MgB2 wires can be substantially decreased with nonmagnetic sheath materials and multifilament structure. In this paper, AC losses of two low loss samples are computed in AC–AC domain, which means that the samples were exposed to alternating transport current and field simultaneously. The losses were computed with modified Brandt’s method, which takes J c(B)-dependence into account, and for these computations, the superconductors’ cross-section is determined directly from photographs. The losses were computed in wide magnetic field range with various transport currents. The results suggest that the AC losses of these samples are relatively low because large magnetization current loops are not formed. Additional simulations show that below the penetration field, the losses can be approximated using constant critical current density based on the self-field critical current of the sample. However, after the penetration field, this leads to too high loss values. Finally, the results are compared to analytical loss formulas in case of sole transport current and sole magnetizing field.