Novel measurement methods of propagation velocity and direction of normal zone in ac superconducting wire

A hybrid method for investigation on the propagation behavior of normal zone in an ac superconducting wire was developed by the combined use of the experimental observations and theoretical calculations. The forced quenching tests with 60 Hz ac current were carried out for a Nb-Ti/Cu-Ni superconducting wire. The local average velocity and direction of normal zone propagation were observed by the noncontact measurement method with capacity type voltage dividers. Simultaneously, the time variation of normal resistance induced in the whole sample was experimentally measured and theoretically calculated. By comparing both derived profiles and referring to the results measured by the noncontact method, we successfully estimated the quench initiation position, propagation velocity and direction of the normal zone in detail.