Simulation of the behavior of superconducting YBCO lines at high current densities

We report on the behavior of YBCO lines at high current densities. The experiments are performed, with short constant current pulses, on Au/YBCO/CeOz structures grown on 2" sapphire wafers. We found that a quasi spontaneous highly dissipative state (HDS) appears at a critical current J*, which is also temperature dependent. The initial propagation velocity of the HDS can reach values as high as 150 m/s for a current of 3J(c). We show experimental evidences that this HDS is driven by the current and does not originate from a thermal runaway of the superconducting line. To confirm these results, we have simulated the thermal behavior of the line, using a calculation based on a finite element method, including the dissipation coming from the flux flow. This model reproduces very well the propagation velocity, and its current dependence, observed experimentally if we include the temperature dependence of J*, whereas the calculated velocities in the case of a purely thermal runaway are one order of magnitude lower. (C) 2002 Elsevier Science B.V. All rights reserved.