50-Hz ac losses in inductive coils with mixed matrix fine filament NbTi composites at fields up to 1 T

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Abstract
Measurements of 50-Hz ac losses were performed using three characteristic NbTi coil samples with ultrafine filaments and a Cu–CuNi mixed matrix at fields up to 1 T and at 4.2 K. Critical current and quenching current densities were measured under dc and ac conditions as well as the losses with their hysteresis and eddy current loss proportions. To characterize the samples by their eddy current loss proportions the transverse resistivity of the matrix ρtrans was determined. The results for losses show that under 50-Hz ac loads alternating fields up to approximately 1 T are attained without quenching. The fact that the associated eddy current losses of about 105 W/m3 remain comparatively low at 0.5 T and 4.2 K opens up for such structured mixed matrix NbTi composites a novel field of application for superconducting generators and pulsed magnets with 50–60 Hz fed windings.