Dynamic magneto-optical imaging of transport current redistribution and normal zone propagation in Ba₂Cu₃O_7-δ coated conductor

YBa₂Cu₃O_7-δ (YBCO) coated conductors carry high critical current density with the potential for low cost and thus have a broad range of potential applications. An unresolved issue that could inhibit implementation, however, is a lack of understanding of the current redistribution and normal zone propagation behavior in the event of a thermal disturbance (quench). In this work, we for the first time present the real-time, dynamic observation of magnetic field redistribution during a thermal disturbance via magneto-optical imaging with a high speed, high resolution CCD (charge coupled device) camera. The optical images are converted to a two-dimensional, time-dependent data set that is then analyzed quantitatively. It is found that the normal zone propagates non-uniformly in two dimensions within the YBCO layer. Two stages of normal zone propagation are observed. During the first stage, the normal zone propagates along the conductor length as the current and magnetic field redistribute within the YBCO layer. During the second stage, current sharing with the Cu begins and the magneto-optical image becomes constant. The normal zone propagation velocity at 45K, I = 50A (∼50%I_c), is determined as 22.7mms^-1 using the time-dependent optical light intensity data.