Magneto-optical study of magnetic-flux penetration into a current-carryinghigh-temperature-superconductor strip

The magnetic-flux distribution across a high-temperature superconductor str ip is measured using magnetooptical imaging at 15 K. Both the current-carry ing state and the remanent state after transport current are studied up to currents of 0.97I(c) where I-c is the critical current. To avoid overheatin g of the sample current pulses with a duration of 50 ms were employed. The results are compared with predictions of the Bean model for the thin strip geometry. In the current-carrying state, reasonable agreement is found. How ever, there is a systematic deviation-the flux penetration is deeper than t heoretically predicted. A much better agreement is achieved by accounting f or Aux creep as shown by our computer simulations. In the remanent state, t he Bean model fails to explain the experimental results. The results for th e currents I less than or equal to 0.7I(c) can be understood within the fra mework of our flux creep simulations. However, after the currents I>0.7I(c) the total flux trapped in a strip is substantially less than predicted by the simulations. Furthermore, it decreases with increasing current. Excessi ve dissipation of power in the annihilation zone formed in the remanent sta te is believed to be the source of this unexpected behavior. [S0163-1829(99 )13313-7].