Transient characteristics of a high-T{sub c} superconductor tube subjected to internal and external magnetic fields.

Transient response of a melt-cast-processed BSCCO-2212 tube at 77 K was studied using a pulsed current supply. Tests were conducted with a copper drive coil either inside or outside the superconductor tube. Experimental results show that the superconductor tube can shield the magnetic field generated by the current in the coil up to a certain limit when the coil is either inside or outside the superconductor tube. Both configurations should work for fault-current limiters. Delayed field penetration (the delay between the penetrated field and the excitation current) was observed in both cases. This delay can be explained by the concept of nonlinear magnetic diffusion, which is valid when the characteristic length of the system is much shorter than the wavelength of the driving field. The rate of magnetic diffusion is increased when (a) the local current density exceeds the critical current density and (b) the local temperature rises as a result of dissipation in the superconductor.