3D Simulation of AC Loss in a 114-filament MgB₂ Wire at 20 K

In future electric aircraft applications employing all-superconducting rotating machines, round multifilamentary magnesium diboride (MgB₂) wires are a preferrable material for lowering AC loss, due to their small filaments at the macron level and tight twist pitch. Our previous work has investigated AC loss behaviour in a 54-filament MgB₂ wire with a filament radius of 12.5 μm, where the filament size was found not ideal for loss reduction. In this work, 3D AC loss simulations of a twisted, non-magnetic 114-filament MgB₂ wire with a 5 μm filament radius at 20 K are performed using <i><b>H</b></i>-formulation. Three types of AC losses are studied: (1) transport loss only (<i>Q</i>_t0, with current levels up to 90% of its self-field critical current <i>I</i>_c0), (2) magnetization loss only (<i>Q</i>_m0, with AC field amplitudes and frequencies up to 2 T and 200 Hz, respectively), (3) total AC loss carrying AC current exposed to AC field (<i>Q</i>_total, with AC field also up to 2 T and current levels up to 40% of <i>I</i>_c0). Simulation results show that, for the <i>Q</i>_m0, the simulated hysteresis loss <i>Q</i>_h of a 5-mm twist pitch, 114-filament wire at 50 Hz and 200 Hz matches the analytical hysteresis loss equation for a cylindrical superconductor, scaled by 114 (the number of filaments), when <i>B</i>_m ≤ 0.5 T. Increasing the twist pitch (5 mm Vs 10 mm) and filament size (5 μm in the 114-filament wire Vs 12.5 μm in the 54-filament wire) leads to a higher <i>Q</i>_m0 due to the coupling effect. Moreover, the simulated <i>Q</i>_total of the 114-filament wire range from 0.22 to 7.48 W/cm³ for <i>i</i> ≤ 0.4 and <i>B</i>_m ≤ 0.5 T operated at 200 Hz.