Dependence of Self Field AC Losses in AC Multifilamentary Composites and Cables on External AC Magnetic Field

Abstract

We measured AC losses of AC multifilamentary wires (NbTi and Nb₃Sn) and a cable of (6+1) configuration due to transport currents in an AC external magnetic field at 50Hz. We also studied the stabilities of the NbTi and Nb₃Sn wires and the cable. The Nb₃Sn AC wire has thinner filamentary zone than the NbTi wire. It was shown by the experiment that the Nb₃Sn wire had better stability against the magnetic instability and that AC quench currents of the Nb₃Sn wire reached the critical current in DC back ground field, while the AC quench currents of the NbTi wire were far below the critical current due to the magnetic instability. The AC losses of the Nb₃Sn wire due to the wire transport current are higher and less dependent on the direction of the external magnetic field than those of the NbTi wire. AC losses of a cable of (6+1) configuration made of the NbTi wire were higher than those estimated from the single wire. Those experimental results are discussed and is explained by estimating thickness of saturated zone in the wire where the filaments carry their critical current.