DYNAMICS OF FAST FLUX-PENETRATION IN HIGH-T-C SUPERCONDUCTORS

A theoretical and experimental study on the magnetic response of high- T-c ceramics to a magnetic field-step is presented. The experiments we re performed on YBCO tubes, either pure or Ag added, by Measuring the flux penetrating into the bore with a pickup coil. This phenomenon was characterized by three parameters: the shielding field H, the penetr ation time Delta t and the time constant tau. The influence on these p arameters of the field-step amplitude, temperature, silver content and compaction pressure of the samples was studied. A theory based on flu x-flow successfully explains the flux penetration phenomenon occurring before the ''critical state'' settles down. This article concludes a series of reports that pioneered the observation of flux dynamics in t he microsecond time scale. A promising application of this theory is t he analysis of transitory phenomena in current limiters and other fast switching devices. (C) 1997 Elsevier Science B.V.