AC loss evaluations of twisted multifilament magnesium diboride (MgB₂) wires under practical operating conditions based on experiments

We measured the frequency-dependent magnetization losses of twisted multifilament MgB 2 wires subjected to ac transverse magnetic fields with a small amplitude, under which coupling loss dominates magnetization loss, and then, we determined their coupling time constants as well as their geometry factors of coupling losses at various temperatures. We also measured the hysteresis loops of their magnetizations using a vibrating sample magnetometer, and then, we calculated the hysteresis losses at various magnetic field amplitudes and at various temperatures. Note that such calculated values represent the hysteresis losses in completely decoupled filaments in a twisted multifilament MgB 2 wire. Using these values obtained experimentally, we calculated the magnetization losses of twisted multifilament MgB 2 wires under practical operating conditions, i.e. at various magnetic field amplitudes, at various magnetic field frequencies, and at various temperatures, considering the saturation of the filamentary region in the wire, which occurs at magnetic fields with high frequencies and large amplitudes.