Magnetisation measurements on technical superconductors at high frequencies (0-42 Hz)

In many applications superconductors are exposed to alternating magnetic fields, sometimes in combination with a DC bias field. Induced eddy currents form closed loops within the resistive matrix material, heat the material and may provoke quenches of the superconductor. Since the total field loss (P/sub lot/=P/sub hysteresis/+P/sub eddycurrent/$ ds) is proportional to the area enclosed by the magnetisation loop it may be found from magnetisation measurements. We perform magnetisation measurements in a hysteresis measurement facility operating with the inductive integration method. The facility operates at liquid helium temperatures (2.0-4.2 K), in a broad frequency range (quasistatic-60 Hz) and offers the possibility to produce simultaneously an AC-field (1 T at 50 Hz) and a DC bias-field (maximally 3.6 T). Measurements in the upper frequency range on NbTi/copper-matrix strands not conceived for AC applications show a peculiar behaviour, namely a deviation from the expected hysteresis loop. We compared the experimentally obtained hysteresis curves to curves obtained with calculations.