AC-losses in multifilamentary superconductors at technical frequencies

Multifilamentary superconductors exposed to an alternating field of small amplitude but in the technical frequency range as in a rotor of a superconducting generator show a characteristic dependence of losses on frequency. Shielding of the conductor by the induced currents is shown to be relevant. In a twisted cylindrical multifilamentary conductor the shielding currents are calculated and formulas for the hysteretic loss and eddy current loss are given as function of frequency and time constant τ of the conductor. It is shown, that a long twist length can give lower losses than a short one.