Superconducting protector against electromagnetic pulses based on YBCO film prepared on an Al₂O₃ substrate with a CeO₂ sublayer

The electric and magnetic properties of microbridges made from 440 nm thick Y–Ba–Cu–O films prepared on Al₂O₃ substrates with CeO₂ sublayers by the pulsed injection metal organic chemical vapor deposition (MOCVD) method were studied in temperatures ranging from 20 K to 300 K in order to investigate the possibilities of using these microbridges as fast fault current limiters. The application of an external magnetic field ($B_{\text{ex}}$) causes the flux flow induced magneto-resistive effect, which is proportional to $B_{\text{ex}}$ and to ${B_{\text{ex}}}^{1/2}$ at low and high temperatures, respectively. The experimentally obtained S-shaped I–V characteristic and the change of the microbridge resistance over time when affected by a step-like magnetic field can be well explained using a thermo-electrical model based on Joule heating and the flux flow nature of the resistive state (RS). The transition from the superconducting to the RS, studied using ns duration rectangular waveform electrical pulses able to create up to ≈2106 A cm⁻² current densities without rises of microbridge temperatures, demonstrated that the I–V characteristics of the RSs consisting of an assembly of straight lines corresponding to the different pinning centers. At temperatures close to the critical temperature of superconductivity, the number of these lines increases, and the I–V characteristics can be described with high accuracy by a power law. It was concluded that microbridges made from these films can be used as protectors against complicated waveform electromagnetic pulses having short rise times, high voltage peak amplitudes and long low-value over-current 'tails'. (paper)