Transient response of a high-temperature superconductor tube to pulsed magnetic fields

The transient response of a melt-cast-processed BSCCO-2212 superconductor mbe under a pulsed magnetic field was investigated by using a pulsed current source driving an external copper solenoid. The induced current in the superconductor tube was measured by a Rogowski coil and the penetration field was measured by a Hall probe inside the tube. It was found that (a) the maximum induced current I-s(max) and the excitation current at field penetration NI* increase with the maximum excitation current NI(max); (b) there is a time delay between peak NI and peak H in tests with relatively low NI(max), and this time delay diminishes in tests with relatively large NI(max); (c) the induced current I-s does not remain constant and begins to decrease immediately after its peak has been reached while the excitation current NI is still increasing; and (d) the decay of the induced current I-s exhibited different behavior between tests with relatively low and high NI(max), the former showed a gradual decay while the latter showed a rapid decay initially and then a nearly constant value for an extended period of time. All of these observations can be explained by magnetic diffusion and a postulated transition from flux-creep to flux-flow behavior. The constant value of induced current after its rapid decay can be interpreted as the steady-state critical current of the superconductor tube. (C) 1998 Published by Elsevier Science B.V. All rights reserved.