MAGNETIC INSTABILITY OF AC MULTIFILAMENTARY WIRE DUE TO TRANSPORT CURRENT AND ITS DEPENDENCE ON PHASE OF EXTERNAL AC MAGNETIC-FIELD

We performed AC quench current of AC superconducting multifilamentary NbTi Nb3Sn wires in AC external field by changing the phase difference between the transport current and the external field, The Nb3Sn AC wi re was more stable than the NbTi wire and the peak value of the AC que nch currents reached to the levels of the DC quench current while the quench current of the NbTi wire was much less than the DC quench curre nt, The data also showed strong dependence of the quench currents on t he phase difference, We made a theoretical model to analyze the stabil ity of AC wire assuming that the instability was caused by the magneti c instability due to the transport currents. In the analysis, wire tem perature was numerically evaluated by calculating instantaneous AC los ses and solving the thermal equibirium equation, and the quench curren t were estimated, In the paper, the experimental results are compared with theoretical ones and it is shown that the theoretical model well explains AC quench behaviors of the wire subject to the external AC ma gnetic field.