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

TL;DR

This study investigates magnetic flux penetration in high-temperature superconductor strips using magneto-optical imaging, comparing experimental results with theoretical models and simulations, revealing deviations due to flux creep and dissipation effects.

Contribution

It provides new insights into flux behavior in superconductors by combining experimental imaging with flux creep simulations, highlighting limitations of the Bean model.

Findings

Flux penetration is deeper than Bean model predictions in the current-carrying state.

Flux creep simulations improve agreement with experimental data.

In the remanent state, flux trapping decreases with increasing current, contrary to expectations.

Abstract

Magnetic flux distribution across a high-temperature superconductor strip is measured using magneto-optical imaging at 15 K. Both the current-carrying state and the remanent state after transport current are studied up to the currents 0.97 Ic where Ic is the critical current. To avoid overheating of the sample current pulses with duration 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. However, there is a systematic deviation -- the flux penetration is deeper than theoretically predicted. A much better agreement is achieved by accounting for flux creep as shown by our computer simulations. In the remanent state the Bean model fails to explain the experimental results. The results for the currents I < 0.7 Ic can be understood within the framework of our flux creep simulations. However, after the currents I > 0.7 Ic the total flux trapped in a strip is substantially less than predicted by the simulations. Furthermore, it decreases with increasing current. Excessive dissipation of power in the annihilation zone formed in the remanent state is believed to be the source of this unexpected behavior.