Measurement of transport critical current of Y-Ba-Cu-O using an inductive method

Abstract

An inductive, contactless procedure discussed by E.A. Harris et al. (Cryogenics, vol.28, p.685-7, 1988) was used to measure two samples of Y-Ba-Cu-O one of which was conventionally sintered, the other prepared using a melt-processing technique. When made into ring form and placed as a tertiary winding on a transformer, the sample could be driven to the normal state and a critical current density determined. It was shown that the melt-processed material has a very large critical current density when compared with the conventionally sintered material, and it exhibits an instantaneous transition to the fully normal state at a well-defined current level. It was found that rapid degradation will occur in melt-processed Y-Ba-Cu-O if it is exposed to condensation after removal from the low-temperature environment. The critical current density invariably decayed during repeated experimentation from a level difficult to achieve with the equipment at hand, to a level not much above the non-melt-processed Y-Ba-Cu-O. The higher levels of measured critical current density could be restored with reoxygenation.